Programs & Examples On #Postgresql

PostgreSQL is an open-source, object-relational database management system (ORDBMS) available for all major platforms including Linux, UNIX, Windows and OS X. Please mention your exact version of Postgres when asking questions. Questions concerning administration or advanced features are best directed to dba.stackexchange.com.

Are PostgreSQL column names case-sensitive?

if use JPA I recommend change to lowercase schema, table and column names, you can use next intructions for help you:

select
    psat.schemaname,
    psat.relname,
    pa.attname,
    psat.relid
from
    pg_catalog.pg_stat_all_tables psat,
    pg_catalog.pg_attribute pa
where
    psat.relid = pa.attrelid

change schema name:

ALTER SCHEMA "XXXXX" RENAME TO xxxxx;

change table names:

ALTER TABLE xxxxx."AAAAA" RENAME TO aaaaa;

change column names:

ALTER TABLE xxxxx.aaaaa RENAME COLUMN "CCCCC" TO ccccc;

Kill a postgresql session/connection

Case :
Fail to execute the query :

DROP TABLE dbo.t_tabelname

Solution :
a. Display query Status Activity as follow :

SELECT * FROM pg_stat_activity  ;

b. Find row where 'Query' column has contains :

'DROP TABLE dbo.t_tabelname'

c. In the same row, get value of 'PID' Column

example : 16409

d. Execute these scripts :

SELECT 
    pg_terminate_backend(25263) 
FROM 
    pg_stat_activity 
WHERE 
    -- don't kill my own connection!
    25263 <> pg_backend_pid()
    -- don't kill the connections to other databases
    AND datname = 'database_name'
    ;

Permanently Set Postgresql Schema Path

(And if you have no admin access to the server)

ALTER ROLE <your_login_role> SET search_path TO a,b,c;

Two important things to know about:

  1. When a schema name is not simple, it needs to be wrapped in double quotes.
  2. The order in which you set default schemas a, b, c matters, as it is also the order in which the schemas will be looked up for tables. So if you have the same table name in more than one schema among the defaults, there will be no ambiguity, the server will always use the table from the first schema you specified for your search_path.

What is the difference between LATERAL and a subquery in PostgreSQL?

The difference between a non-lateral and a lateral join lies in whether you can look to the left hand table's row. For example:

select  *
from    table1 t1
cross join lateral
        (
        select  *
        from    t2
        where   t1.col1 = t2.col1 -- Only allowed because of lateral
        ) sub

This "outward looking" means that the subquery has to be evaluated more than once. After all, t1.col1 can assume many values.

By contrast, the subquery after a non-lateral join can be evaluated once:

select  *
from    table1 t1
cross join
        (
        select  *
        from    t2
        where   t2.col1 = 42 -- No reference to outer query
        ) sub

As is required without lateral, the inner query does not depend in any way on the outer query. A lateral query is an example of a correlated query, because of its relation with rows outside the query itself.

Postgres "psql not recognized as an internal or external command"

If you tried all the answers and still spinning your heads, don't forget to change the version with your one which you downloaded.

For example, don't simply copy paste

;C:\Program Files\PostgreSQL\9.5\bin ;C:\Program Files\PostgreSQL\9.5\lib

More clearly,

;C:\Program Files\PostgreSQL\[Your Version]\bin ;C:\Program Files\PostgreSQL\[Your Version]\lib

I was spinning my heads. Hope this helps.

How to use (install) dblink in PostgreSQL?

It can be added by using:

$psql -d databaseName -c "CREATE EXTENSION dblink"

PostgreSQL: days/months/years between two dates

I would like to expand on Riki_tiki_tavi's answer and get the data out there. I have created a datediff function that does almost everything sql server does. So that way we can take into account any unit.

create function datediff(units character varying, start_t timestamp without time zone, end_t timestamp without time zone) returns integer
language plpgsql
 as
 $$
DECLARE
 diff_interval INTERVAL; 
 diff INT = 0;
 years_diff INT = 0;
BEGIN
 IF units IN ('yy', 'yyyy', 'year', 'mm', 'm', 'month') THEN
   years_diff = DATE_PART('year', end_t) - DATE_PART('year', start_t);

   IF units IN ('yy', 'yyyy', 'year') THEN
     -- SQL Server does not count full years passed (only difference between year parts)
     RETURN years_diff;
   ELSE
     -- If end month is less than start month it will subtracted
     RETURN years_diff * 12 + (DATE_PART('month', end_t) - DATE_PART('month', start_t)); 
   END IF;
 END IF;

 -- Minus operator returns interval 'DDD days HH:MI:SS'  
 diff_interval = end_t - start_t;

 diff = diff + DATE_PART('day', diff_interval);

 IF units IN ('wk', 'ww', 'week') THEN
   diff = diff/7;
   RETURN diff;
 END IF;

 IF units IN ('dd', 'd', 'day') THEN
   RETURN diff;
 END IF;

 diff = diff * 24 + DATE_PART('hour', diff_interval); 

 IF units IN ('hh', 'hour') THEN
    RETURN diff;
 END IF;

 diff = diff * 60 + DATE_PART('minute', diff_interval);

 IF units IN ('mi', 'n', 'minute') THEN
    RETURN diff;
 END IF;

 diff = diff * 60 + DATE_PART('second', diff_interval);

 RETURN diff;
END;
$$;

PostgreSQL "DESCRIBE TABLE"

In addition to the command line \d+ <table_name> you already found, you could also use the information-schema to look up the column data, using info_schema.columns

SELECT *
FROM info_schema.columns
WHERE table_schema = 'your_schema'
AND table_name   = 'your_table'

Postgres password authentication fails

pg_hba.conf entry define login methods by IP addresses. You need to show the relevant portion of pg_hba.conf in order to get proper help.

Change this line:

host    all             all             <my-ip-address>/32        md5

To reflect your local network settings. So, if your IP is 192.168.16.78 (class C) with a mask of 255.255.255.0, then put this:

host    all             all             192.168.16.0/24        md5

Make sure your WINDOWS MACHINE is in that network 192.168.16.0 and try again.

Check if value exists in Postgres array

Watch out for the trap I got into: When checking if certain value is not present in an array, you shouldn't do:

SELECT value_variable != ANY('{1,2,3}'::int[])

but use

SELECT value_variable != ALL('{1,2,3}'::int[])

instead.

Simulate CREATE DATABASE IF NOT EXISTS for PostgreSQL?

Just create the database using createdb CLI tool:

PGHOST="my.database.domain.com"
PGUSER="postgres"
PGDB="mydb"
createdb -h $PGHOST -p $PGPORT -U $PGUSER $PGDB

If the database exists, it will return an error:

createdb: database creation failed: ERROR:  database "mydb" already exists

Postgres could not connect to server

The Cause

Lion comes with a version of postgres already installed and uses those binaries by default. In general you can get around this by using the full path to the homebrew postgres binaries but there may be still issues with other programs.

The Solution

curl http://nextmarvel.net/blog/downloads/fixBrewLionPostgres.sh | sh

Via

http://nextmarvel.net/blog/2011/09/brew-install-postgresql-on-os-x-lion/

Generate a random number in the range 1 - 10

The correct version of hythlodayr's answer.

-- ERROR:  operator does not exist: double precision % integer
-- LINE 1: select (trunc(random() * 10) % 10) + 1

The output from trunc has to be converted to INTEGER. But it can be done without trunc. So it turns out to be simple.

select (random() * 9)::INTEGER + 1

Generates an INTEGER output in range [1, 10] i.e. both 1 & 10 inclusive.

For any number (floats), see user80168's answer. i.e just don't convert it to INTEGER.

How can I get a list of all functions stored in the database of a particular schema in PostgreSQL?

Is a good idea named the functions with commun alias on the first words for filtre the name with LIKE Example with public schema in Postgresql 9.4, be sure to replace with his scheme

SELECT routine_name 
FROM information_schema.routines 
WHERE routine_type='FUNCTION' 
  AND specific_schema='public'
  AND routine_name LIKE 'aliasmyfunctions%';

What GRANT USAGE ON SCHEMA exactly do?

Well, this is my final solution for a simple db, for Linux:

# Read this before!
#
# * roles in postgres are users, and can be used also as group of users
# * $ROLE_LOCAL will be the user that access the db for maintenance and
#   administration. $ROLE_REMOTE will be the user that access the db from the webapp
# * you have to change '$ROLE_LOCAL', '$ROLE_REMOTE' and '$DB'
#   strings with your desired names
# * it's preferable that $ROLE_LOCAL == $DB

#-------------------------------------------------------------------------------

//----------- SKIP THIS PART UNTIL POSTGRES JDBC ADDS SCRAM - START ----------//

cd /etc/postgresql/$VERSION/main
sudo cp pg_hba.conf pg_hba.conf_bak
sudo -e pg_hba.conf

# change all `md5` with `scram-sha-256`
# save and exit

//------------ SKIP THIS PART UNTIL POSTGRES JDBC ADDS SCRAM - END -----------//

sudo -u postgres psql

# in psql:
create role $ROLE_LOCAL login createdb;
\password $ROLE_LOCAL
create role $ROLE_REMOTE login;
\password $ROLE_REMOTE

create database $DB owner $ROLE_LOCAL encoding "utf8";
\connect $DB $ROLE_LOCAL

# Create all tables and objects, and after that:

\connect $DB postgres

revoke connect on database $DB from public;
revoke all on schema public from public;
revoke all on all tables in schema public from public;

grant connect on database $DB to $ROLE_LOCAL;
grant all on schema public to $ROLE_LOCAL;
grant all on all tables in schema public to $ROLE_LOCAL;
grant all on all sequences in schema public to $ROLE_LOCAL;
grant all on all functions in schema public to $ROLE_LOCAL;

grant connect on database $DB to $ROLE_REMOTE;
grant usage on schema public to $ROLE_REMOTE;
grant select, insert, update, delete on all tables in schema public to $ROLE_REMOTE;
grant usage, select on all sequences in schema public to $ROLE_REMOTE;
grant execute on all functions in schema public to $ROLE_REMOTE;

alter default privileges for role $ROLE_LOCAL in schema public
    grant all on tables to $ROLE_LOCAL;

alter default privileges for role $ROLE_LOCAL in schema public
    grant all on sequences to $ROLE_LOCAL;

alter default privileges for role $ROLE_LOCAL in schema public
    grant all on functions to $ROLE_LOCAL;

alter default privileges for role $ROLE_REMOTE in schema public
    grant select, insert, update, delete on tables to $ROLE_REMOTE;

alter default privileges for role $ROLE_REMOTE in schema public
    grant usage, select on sequences to $ROLE_REMOTE;

alter default privileges for role $ROLE_REMOTE in schema public
    grant execute on functions to $ROLE_REMOTE;

# CTRL+D

How to return result of a SELECT inside a function in PostgreSQL?

Hi please check the below link

https://www.postgresql.org/docs/current/xfunc-sql.html

EX:

CREATE FUNCTION sum_n_product_with_tab (x int)
RETURNS TABLE(sum int, product int) AS $$
    SELECT $1 + tab.y, $1 * tab.y FROM tab;
$$ LANGUAGE SQL;

PostgreSQL naming conventions

There isn't really a formal manual, because there's no single style or standard.

So long as you understand the rules of identifier naming you can use whatever you like.

In practice, I find it easier to use lower_case_underscore_separated_identifiers because it isn't necessary to "Double Quote" them everywhere to preserve case, spaces, etc.

If you wanted to name your tables and functions "@MyA??! ""betty"" Shard$42" you'd be free to do that, though it'd be pain to type everywhere.

The main things to understand are:

  • Unless double-quoted, identifiers are case-folded to lower-case, so MyTable, MYTABLE and mytable are all the same thing, but "MYTABLE" and "MyTable" are different;

  • Unless double-quoted:

    SQL identifiers and key words must begin with a letter (a-z, but also letters with diacritical marks and non-Latin letters) or an underscore (_). Subsequent characters in an identifier or key word can be letters, underscores, digits (0-9), or dollar signs ($).

  • You must double-quote keywords if you wish to use them as identifiers.

In practice I strongly recommend that you do not use keywords as identifiers. At least avoid reserved words. Just because you can name a table "with" doesn't mean you should.

How to use SQL LIKE condition with multiple values in PostgreSQL?

You can use regular expression operator (~), separated by (|) as described in Pattern Matching

select column_a from table where column_a ~* 'aaa|bbb|ccc'

hibernate could not get next sequence value

I would also like to add a few notes about a MySQL-to-PostgreSQL migration:

  1. In your DDL, in the object naming prefer the use of '_' (underscore) character for word separation to the camel case convention. The latter works fine in MySQL but brings a lot of issues in PostgreSQL.
  2. The IDENTITY strategy for @GeneratedValue annotation in your model class-identity fields works fine for PostgreSQLDialect in hibernate 3.2 and superior. Also, The AUTO strategy is the typical setting for MySQLDialect.
  3. If you annotate your model classes with @Table and set a literal value to these equal to the table name, make sure you did create the tables to be stored under public schema.

That's as far as I remember now, hope these tips can spare you a few minutes of trial and error fiddling!

How do I get the current timezone name in Postgres 9.3?

You can access the timezone by the following script:

SELECT * FROM pg_timezone_names WHERE name = current_setting('TIMEZONE');
  • current_setting('TIMEZONE') will give you Continent / Capital information of settings
  • pg_timezone_names The view pg_timezone_names provides a list of time zone names that are recognized by SET TIMEZONE, along with their associated abbreviations, UTC offsets, and daylight-savings status.
  • name column in a view (pg_timezone_names) is time zone name.

output will be :

name- Europe/Berlin, 
abbrev - CET, 
utc_offset- 01:00:00, 
is_dst- false

Adding a new value to an existing ENUM Type

Disclaimer: I haven't tried this solution, so it might not work ;-)

You should be looking at pg_enum. If you only want to change the label of an existing ENUM, a simple UPDATE will do it.

To add a new ENUM values:

  • First insert the new value into pg_enum. If the new value has to be the last, you're done.
  • If not (you need to a new ENUM value in between existing ones), you'll have to update each distinct value in your table, going from the uppermost to the lowest...
  • Then you'll just have to rename them in pg_enum in the opposite order.

Illustration
You have the following set of labels:

ENUM ('enum1', 'enum2', 'enum3')

and you want to obtain:

ENUM ('enum1', 'enum1b', 'enum2', 'enum3')

then:

INSERT INTO pg_enum (OID, 'newenum3');
UPDATE TABLE SET enumvalue TO 'newenum3' WHERE enumvalue='enum3';
UPDATE TABLE SET enumvalue TO 'enum3' WHERE enumvalue='enum2';

then:

UPDATE TABLE pg_enum SET name='enum1b' WHERE name='enum2' AND enumtypid=OID;

And so on...

How to pass in password to pg_dump?

the easiest way in my opinion, this: you edit you main postgres config file: pg_hba.conf there you have to add the following line:

host <you_db_name> <you_db_owner> 127.0.0.1/32 trust

and after this you need start you cron thus:

pg_dump -h 127.0.0.1 -U <you_db_user> <you_db_name> | gzip > /backup/db/$(date +%Y-%m-%d).psql.gz

and it worked without password

Postgresql, update if row with some unique value exists, else insert

If INSERTS are rare, I would avoid doing a NOT EXISTS (...) since it emits a SELECT on all updates. Instead, take a look at wildpeaks answer: https://dba.stackexchange.com/questions/5815/how-can-i-insert-if-key-not-exist-with-postgresql

CREATE OR REPLACE FUNCTION upsert_tableName(arg1 type, arg2 type) RETURNS VOID AS $$ 
    DECLARE 
    BEGIN 
        UPDATE tableName SET col1 = value WHERE colX = arg1 and colY = arg2; 
        IF NOT FOUND THEN 
        INSERT INTO tableName values (value, arg1, arg2); 
        END IF; 
    END; 
    $$ LANGUAGE 'plpgsql'; 

This way Postgres will initially try to do a UPDATE. If no rows was affected, it will fall back to emitting an INSERT.

PostgreSQL unnest() with element number

Postgres 9.4 or later

Use WITH ORDINALITY for set-returning functions:

When a function in the FROM clause is suffixed by WITH ORDINALITY, a bigint column is appended to the output which starts from 1 and increments by 1 for each row of the function's output. This is most useful in the case of set returning functions such as unnest().

In combination with the LATERAL feature in pg 9.3+, and according to this thread on pgsql-hackers, the above query can now be written as:

SELECT t.id, a.elem, a.nr
FROM   tbl AS t
LEFT   JOIN LATERAL unnest(string_to_array(t.elements, ','))
                    WITH ORDINALITY AS a(elem, nr) ON TRUE;

LEFT JOIN ... ON TRUE preserves all rows in the left table, even if the table expression to the right returns no rows. If that's of no concern you can use this otherwise equivalent, less verbose form with an implicit CROSS JOIN LATERAL:

SELECT t.id, a.elem, a.nr
FROM   tbl t, unnest(string_to_array(t.elements, ',')) WITH ORDINALITY a(elem, nr);

Or simpler if based off an actual array (arr being an array column):

SELECT t.id, a.elem, a.nr
FROM   tbl t, unnest(t.arr) WITH ORDINALITY a(elem, nr);

Or even, with minimal syntax:

SELECT id, a, ordinality
FROM   tbl, unnest(arr) WITH ORDINALITY a;

a is automatically table and column alias. The default name of the added ordinality column is ordinality. But it's better (safer, cleaner) to add explicit column aliases and table-qualify columns.

Postgres 8.4 - 9.3

With row_number() OVER (PARTITION BY id ORDER BY elem) you get numbers according to the sort order, not the ordinal number of the original ordinal position in the string.

You can simply omit ORDER BY:

SELECT *, row_number() OVER (PARTITION by id) AS nr
FROM  (SELECT id, regexp_split_to_table(elements, ',') AS elem FROM tbl) t;

While this normally works and I have never seen it fail in simple queries, PostgreSQL asserts nothing concerning the order of rows without ORDER BY. It happens to work due to an implementation detail.

To guarantee ordinal numbers of elements in the blank-separated string:

SELECT id, arr[nr] AS elem, nr
FROM  (
   SELECT *, generate_subscripts(arr, 1) AS nr
   FROM  (SELECT id, string_to_array(elements, ' ') AS arr FROM tbl) t
   ) sub;

Or simpler if based off an actual array:

SELECT id, arr[nr] AS elem, nr
FROM  (SELECT *, generate_subscripts(arr, 1) AS nr FROM tbl) t;

Related answer on dba.SE:

Postgres 8.1 - 8.4

None of these features are available, yet: RETURNS TABLE, generate_subscripts(), unnest(), array_length(). But this works:

CREATE FUNCTION f_unnest_ord(anyarray, OUT val anyelement, OUT ordinality integer)
  RETURNS SETOF record
  LANGUAGE sql IMMUTABLE AS
'SELECT $1[i], i - array_lower($1,1) + 1
 FROM   generate_series(array_lower($1,1), array_upper($1,1)) i';

Note in particular, that the array index can differ from ordinal positions of elements. Consider this demo with an extended function:

CREATE FUNCTION f_unnest_ord_idx(anyarray, OUT val anyelement, OUT ordinality int, OUT idx int)
  RETURNS SETOF record
  LANGUAGE sql IMMUTABLE AS
'SELECT $1[i], i - array_lower($1,1) + 1, i
 FROM   generate_series(array_lower($1,1), array_upper($1,1)) i';

SELECT id, arr, (rec).*
FROM  (
   SELECT *, f_unnest_ord_idx(arr) AS rec
   FROM  (VALUES (1, '{a,b,c}'::text[])  --  short for: '[1:3]={a,b,c}'
               , (2, '[5:7]={a,b,c}')
               , (3, '[-9:-7]={a,b,c}')
      ) t(id, arr)
   ) sub;

 id |       arr       | val | ordinality | idx
----+-----------------+-----+------------+-----
  1 | {a,b,c}         | a   |          1 |   1
  1 | {a,b,c}         | b   |          2 |   2
  1 | {a,b,c}         | c   |          3 |   3
  2 | [5:7]={a,b,c}   | a   |          1 |   5
  2 | [5:7]={a,b,c}   | b   |          2 |   6
  2 | [5:7]={a,b,c}   | c   |          3 |   7
  3 | [-9:-7]={a,b,c} | a   |          1 |  -9
  3 | [-9:-7]={a,b,c} | b   |          2 |  -8
  3 | [-9:-7]={a,b,c} | c   |          3 |  -7

Compare:

Online SQL syntax checker conforming to multiple databases

Only know about this. Not sure how well does it against MySQL http://developer.mimer.se/validator/

Fastest check if row exists in PostgreSQL

INSERT INTO target( userid, rightid, count )
  SELECT userid, rightid, count 
  FROM batch
  WHERE NOT EXISTS (
    SELECT * FROM target t2, batch b2
    WHERE t2.userid = b2.userid
    -- ... other keyfields ...
    )       
    ;

BTW: if you want the whole batch to fail in case of a duplicate, then (given a primary key constraint)

INSERT INTO target( userid, rightid, count )
SELECT userid, rightid, count 
FROM batch
    ;

will do exactly what you want: either it succeeds, or it fails.

PostgreSQL: Show tables in PostgreSQL

If you are using pgAdmin4 in PostgreSQL, you can use this to show the tables in your database:

select * from information_schema.tables where table_schema='public';

How to add an auto-incrementing primary key to an existing table, in PostgreSQL?

To use an identity column in v10,

ALTER TABLE test 
ADD COLUMN id { int | bigint | smallint}
GENERATED { BY DEFAULT | ALWAYS } AS IDENTITY PRIMARY KEY;

For an explanation of identity columns, see https://blog.2ndquadrant.com/postgresql-10-identity-columns/.

For the difference between GENERATED BY DEFAULT and GENERATED ALWAYS, see https://www.cybertec-postgresql.com/en/sequences-gains-and-pitfalls/.

For altering the sequence, see https://popsql.io/learn-sql/postgresql/how-to-alter-sequence-in-postgresql/.

Postgresql Windows, is there a default password?

Try this:

Open PgAdmin -> Files -> Open pgpass.conf

You would get the path of pgpass.conf at the bottom of the window. Go to that location and open this file, you can find your password there.

Reference

If the above does not work, you may consider trying this:

 1. edit pg_hba.conf to allow trust authorization temporarily
 2. Reload the config file (pg_ctl reload)
 3. Connect and issue ALTER ROLE / PASSWORD to set the new password
 4. edit pg_hba.conf again and restore the previous settings
 5. Reload the config file again

Oracle SQL Developer and PostgreSQL

I got the list of databases to populate by putting my username in the Username field (no password) and clicking "Choose Database". Doesn't work with a blank Username field, I can only connect to my user database that way.

(This was with SQL Developer 4.0.0.13, Postgres.app 9.3.0.0, and postgresql-9.3-1100.jdbc41.jar, FWIW.)

Insert Data Into Tables Linked by Foreign Key

Use stored procedures.

And even assuming you would want not to use stored procedures - there is at most 3 commands to be run, not 4. Second getting id is useless, as you can do "INSERT INTO ... RETURNING".

What is PostgreSQL equivalent of SYSDATE from Oracle?

SYSDATE is an Oracle only function.

The ANSI standard defines current_date or current_timestamp which is supported by Postgres and documented in the manual:
http://www.postgresql.org/docs/current/static/functions-datetime.html#FUNCTIONS-DATETIME-CURRENT

(Btw: Oracle supports CURRENT_TIMESTAMP as well)

You should pay attention to the difference between current_timestamp, statement_timestamp() and clock_timestamp() (which is explained in the manual, see the above link)


This statement:

select up_time from exam where up_time like sysdate

Does not make any sense at all. Neither in Oracle nor in Postgres. If you want to get rows from "today", you need something like:

select up_time 
from exam 
where up_time = current_date

Note that in Oracle you would probably want trunc(up_time) = trunc(sysdate) to get rid of the time part that is always included in Oracle.

How do I force Postgres to use a particular index?

There is a trick to push postgres to prefer a seqscan adding a OFFSET 0 in the subquery

This is handy for optimizing requests linking big/huge tables when all you need is only the n first/last elements.

Lets say you are looking for first/last 20 elements involving multiple tables having 100k (or more) entries, no point building/linking up all the query over all the data when what you'll be looking for is in the first 100 or 1000 entries. In this scenario for example, it turns out to be over 10x faster to do a sequential scan.

see How can I prevent Postgres from inlining a subquery?

Insert text with single quotes in PostgreSQL

This is so many worlds of bad, because your question implies that you probably have gaping SQL injection holes in your application.

You should be using parameterized statements. For Java, use PreparedStatement with placeholders. You say you don't want to use parameterised statements, but you don't explain why, and frankly it has to be a very good reason not to use them because they're the simplest, safest way to fix the problem you are trying to solve.

See Preventing SQL Injection in Java. Don't be Bobby's next victim.

There is no public function in PgJDBC for string quoting and escaping. That's partly because it might make it seem like a good idea.

There are built-in quoting functions quote_literal and quote_ident in PostgreSQL, but they are for PL/PgSQL functions that use EXECUTE. These days quote_literal is mostly obsoleted by EXECUTE ... USING, which is the parameterised version, because it's safer and easier. You cannot use them for the purpose you explain here, because they're server-side functions.


Imagine what happens if you get the value ');DROP SCHEMA public;-- from a malicious user. You'd produce:

insert into test values (1,'');DROP SCHEMA public;--');

which breaks down to two statements and a comment that gets ignored:

insert into test values (1,'');
DROP SCHEMA public;
--');

Whoops, there goes your database.

psql: command not found Mac

From the Postgres documentation page:

sudo mkdir -p /etc/paths.d && echo /Applications/Postgres.app/Contents/Versions/latest/bin | sudo tee /etc/paths.d/postgresapp

restart your terminal and you will have it in your path.

No function matches the given name and argument types

In my particular case the function was actually missing. The error message is the same. I am using the Postgresql plugin PostGIS and I had to reinstall that for whatever reason.

change pgsql port

You can also change the port when starting up:

$ pg_ctl -o "-F -p 5433" start

Or

$ postgres -p 5433

More about this in the manual.

Import Excel Data into PostgreSQL 9.3

The typical answer is this:

  1. In Excel, File/Save As, select CSV, save your current sheet.

  2. transfer to a holding directory on the Pg server the postgres user can access

  3. in PostgreSQL:

    COPY mytable FROM '/path/to/csv/file' WITH CSV HEADER; -- must be superuser
    

But there are other ways to do this too. PostgreSQL is an amazingly programmable database. These include:

  1. Write a module in pl/javaU, pl/perlU, or other untrusted language to access file, parse it, and manage the structure.

  2. Use CSV and the fdw_file to access it as a pseudo-table

  3. Use DBILink and DBD::Excel

  4. Write your own foreign data wrapper for reading Excel files.

The possibilities are literally endless....

Concatenate multiple result rows of one column into one, group by another column

You can use array_agg function for that:

SELECT "Movie",
array_to_string(array_agg(distinct "Actor"),',') AS Actor
FROM Table1
GROUP BY "Movie";

Result:

MOVIE ACTOR
A 1,2,3
B 4

See this SQLFiddle

For more See 9.18. Aggregate Functions

Fatal error: Call to undefined function pg_connect()

If you got php5.6 using the ppa repository http://ppa.launchpad.net/ondrej/php/ubuntu,

then you should install the package using:

sudo apt install php5.6-pgsql

Finally, if you use apache2, restart it:

sudo service apache2 restart

IN Clause with NULL or IS NULL

Null refers to an absence of data. Null is formally defined as a value that is unavailable, unassigned, unknown or inapplicable (OCA Oracle Database 12c, SQL Fundamentals I Exam Guide, p87). So, you may not see records with columns containing null values when said columns are restricted using an "in" or "not in" clauses.

org.postgresql.util.PSQLException: FATAL: sorry, too many clients already

The offending lines are the following:

MaxConnections=90
InitialConnections=80

You can increase the values to allow more connections.

String literals and escape characters in postgresql

Really stupid question: Are you sure the string is being truncated, and not just broken at the linebreak you specify (and possibly not showing in your interface)? Ie, do you expect the field to show as

This will be inserted \n This will not be

or

This will be inserted

This will not be

Also, what interface are you using? Is it possible that something along the way is eating your backslashes?

password for postgres

What's the default superuser username/password for postgres after a new install?:

CAUTION The answer about changing the UNIX password for "postgres" through "$ sudo passwd postgres" is not preferred, and can even be DANGEROUS!

This is why: By default, the UNIX account "postgres" is locked, which means it cannot be logged in using a password. If you use "sudo passwd postgres", the account is immediately unlocked. Worse, if you set the password to something weak, like "postgres", then you are exposed to a great security danger. For example, there are a number of bots out there trying the username/password combo "postgres/postgres" to log into your UNIX system.

What you should do is follow Chris James's answer:

sudo -u postgres psql postgres

# \password postgres

Enter new password: 

To explain it a little bit...

good postgresql client for windows?

I recommend Navicat strongly. What I found particularly excellent are it's import functions - you can import almost any data format (Access, Excel, DBF, Lotus ...), define a mapping between the source and destination which can be saved and is repeatable (I even keep my mappings under version control).

I have tried SQLMaestro and found it buggy (particularly for data import); PGAdmin is limited.

PostgreSQL error: Fatal: role "username" does not exist

psql postgres

postgres=# CREATE ROLE username superuser;
postgres=# ALTER ROLE username WITH LOGIN;

How do I change column default value in PostgreSQL?

If you want to remove the default value constraint, you can do:

ALTER TABLE <table> ALTER COLUMN <column> DROP DEFAULT;

Increment a value in Postgres

UPDATE totals 
   SET total = total + 1
WHERE name = 'bill';

If you want to make sure the current value is indeed 203 (and not accidently increase it again) you can also add another condition:

UPDATE totals 
   SET total = total + 1
WHERE name = 'bill'
  AND total = 203;

Update multiple rows in same query using PostgreSQL

Yes, you can:

UPDATE foobar SET column_a = CASE
   WHEN column_b = '123' THEN 1
   WHEN column_b = '345' THEN 2
END
WHERE column_b IN ('123','345')

And working proof: http://sqlfiddle.com/#!2/97c7ea/1

Best practices for SQL varchar column length

I haven't checked this lately, but I know in the past with Oracle that the JDBC driver would reserve a chunk of memory during query execution to hold the result set coming back. The size of the memory chunk is dependent on the column definitions and the fetch size. So the length of the varchar2 columns affects how much memory is reserved. This caused serious performance issues for me years ago as we always used varchar2(4000) (the max at the time) and garbage collection was much less efficient than it is today.

How do I enable php to work with postgresql?

You need to install the pgsql module for php. In debian/ubuntu is something like this:

sudo apt-get install php5-pgsql

Or if the package is installed, you need to enable de module in php.ini

extension=php_pgsql.dll (windows)
extension=php_pgsql.so (linux)

Greatings.

GUI Tool for PostgreSQL

Postgres Enterprise Manager from EnterpriseDB is probably the most advanced you'll find. It includes all the features of pgAdmin, plus monitoring of your hosts and database servers, predictive reporting, alerting and a SQL Profiler.

http://www.enterprisedb.com/products-services-training/products/postgres-enterprise-manager

Ninja edit disclaimer/notice: it seems that this user is affiliated with EnterpriseDB, as the linked Postgres Enterprise Manager website contains a video of one Dave Page.

Completely uninstall PostgreSQL 9.0.4 from Mac OSX Lion?

Uninstallation :

sudo /Library/PostgreSQL/9.6/uninstall-postgresql.app/Contents/MacOS/installbuilder.sh

Removing the data file :

sudo rm -rf /Library/PostgreSQL

Removing the configs :

sudo rm /etc/postgres-reg.ini

And thats it.

postgresql - replace all instances of a string within text field

You can use the replace function

UPDATE your_table SET field = REPLACE(your_field, 'cat','dog')

The function definition is as follows (got from here):

replace(string text, from text, to text)

and returns the modified text. You can also check out this sql fiddle.

How to declare local variables in postgresql?

Postgresql historically doesn't support procedural code at the command level - only within functions. However, in Postgresql 9, support has been added to execute an inline code block that effectively supports something like this, although the syntax is perhaps a bit odd, and there are many restrictions compared to what you can do with SQL Server. Notably, the inline code block can't return a result set, so can't be used for what you outline above.

In general, if you want to write some procedural code and have it return a result, you need to put it inside a function. For example:

CREATE OR REPLACE FUNCTION somefuncname() RETURNS int LANGUAGE plpgsql AS $$
DECLARE
  one int;
  two int;
BEGIN
  one := 1;
  two := 2;
  RETURN one + two;
END
$$;
SELECT somefuncname();

The PostgreSQL wire protocol doesn't, as far as I know, allow for things like a command returning multiple result sets. So you can't simply map T-SQL batches or stored procedures to PostgreSQL functions.

How do you use script variables in psql?

I solved it with a temp table.

CREATE TEMP TABLE temp_session_variables (
    "sessionSalt" TEXT
);
INSERT INTO temp_session_variables ("sessionSalt") VALUES (current_timestamp || RANDOM()::TEXT);

This way, I had a "variable" I could use over multiple queries, that is unique for the session. I needed it to generate unique "usernames" while still not having collisions if importing users with the same user name.

psycopg2: insert multiple rows with one query

Using aiopg - The snippet below works perfectly fine

    # items = [10, 11, 12, 13]
    # group = 1
    tup = [(gid, pid) for pid in items]
    args_str = ",".join([str(s) for s in tup])
    # insert into group values (1, 10), (1, 11), (1, 12), (1, 13)
    yield from cur.execute("INSERT INTO group VALUES " + args_str)

How to import existing *.sql files in PostgreSQL 8.4?

in command line first reach the directory where psql is present then write commands like this:

psql [database name] [username]

and then press enter psql asks for password give the user password:

then write

> \i [full path and file name with extension]

then press enter insertion done.

printing a value of a variable in postgresql

You can raise a notice in Postgres as follows:

raise notice 'Value: %', deletedContactId;

Read here

How can I start PostgreSQL server on Mac OS X?

For completeness sake: Check whether you're inside a Tmux or Screen instance. Starting won't work from there.

From: Error while trying to start PostgreSQL installed via Homebrew: “Operation not permitted”

This solved it for me.

PostgreSQL ERROR: canceling statement due to conflict with recovery

Running queries on hot-standby server is somewhat tricky — it can fail, because during querying some needed rows might be updated or deleted on primary. As a primary does not know that a query is started on secondary it thinks it can clean up (vacuum) old versions of its rows. Then secondary has to replay this cleanup, and has to forcibly cancel all queries which can use these rows.

Longer queries will be canceled more often.

You can work around this by starting a repeatable read transaction on primary which does a dummy query and then sits idle while a real query is run on secondary. Its presence will prevent vacuuming of old row versions on primary.

More on this subject and other workarounds are explained in Hot Standby — Handling Query Conflicts section in documentation.

Using COALESCE to handle NULL values in PostgreSQL

You can use COALESCE in conjunction with NULLIF for a short, efficient solution:

COALESCE( NULLIF(yourField,'') , '0' )

The NULLIF function will return null if yourField is equal to the second value ('' in the example), making the COALESCE function fully working on all cases:

                 QUERY                     |                RESULT 
---------------------------------------------------------------------------------
SELECT COALESCE(NULLIF(null  ,''),'0')     |                 '0'
SELECT COALESCE(NULLIF(''    ,''),'0')     |                 '0'
SELECT COALESCE(NULLIF('foo' ,''),'0')     |                 'foo'

Split comma separated column data into additional columns

If the number of fields in the CSV is constant then you could do something like this:

select a[1], a[2], a[3], a[4]
from (
    select regexp_split_to_array('a,b,c,d', ',')
) as dt(a)

For example:

=> select a[1], a[2], a[3], a[4] from (select regexp_split_to_array('a,b,c,d', ',')) as dt(a);
 a | a | a | a 
---+---+---+---
 a | b | c | d
(1 row)

If the number of fields in the CSV is not constant then you could get the maximum number of fields with something like this:

select max(array_length(regexp_split_to_array(csv, ','), 1))
from your_table

and then build the appropriate a[1], a[2], ..., a[M] column list for your query. So if the above gave you a max of 6, you'd use this:

select a[1], a[2], a[3], a[4], a[5], a[6]
from (
    select regexp_split_to_array(csv, ',')
    from your_table
) as dt(a)

You could combine those two queries into a function if you wanted.

For example, give this data (that's a NULL in the last row):

=> select * from csvs;
     csv     
-------------
 1,2,3
 1,2,3,4
 1,2,3,4,5,6

(4 rows)

=> select max(array_length(regexp_split_to_array(csv, ','), 1)) from csvs;
 max 
-----
   6
(1 row)

=> select a[1], a[2], a[3], a[4], a[5], a[6] from (select regexp_split_to_array(csv, ',') from csvs) as dt(a);
 a | a | a | a | a | a 
---+---+---+---+---+---
 1 | 2 | 3 |   |   | 
 1 | 2 | 3 | 4 |   | 
 1 | 2 | 3 | 4 | 5 | 6
   |   |   |   |   | 
(4 rows)

Since your delimiter is a simple fixed string, you could also use string_to_array instead of regexp_split_to_array:

select ...
from (
    select string_to_array(csv, ',')
    from csvs
) as dt(a);

Thanks to Michael for the reminder about this function.

You really should redesign your database schema to avoid the CSV column if at all possible. You should be using an array column or a separate table instead.

How can I merge the columns from two tables into one output?

When your are three tables or more, just add union and left outer join:

select a.col1, b.col2, a.col3, b.col4, a.category_id 
from 
(
    select category_id from a
    union
    select category_id from b
) as c
left outer join a on a.category_id = c.category_id
left outer join b on b.category_id = c.category_id

No operator matches the given name and argument type(s). You might need to add explicit type casts. -- Netbeans, Postgresql 8.4 and Glassfish

I had this problem when i was trying to query by passing a Set and i didn't used In

example

problem : repository.findBySomeSetOfData(setOfData);

solution : repository.findBySomeSetOfDataIn(setOfData);

How do I connect C# with Postgres?

If you want an recent copy of npgsql, then go here

http://www.npgsql.org/

This can be installed via package manager console as

PM> Install-Package Npgsql

Rails and PostgreSQL: Role postgres does not exist

I ended up here after attempting to follow Ryan Bate's tutorial on deploying to AWS EC2 with rubber. Here is what happened for me: We created a new app using "

rails new blog -d postgresql

Obviosuly this creates a new app with pg as the database, but the database was not made yet. With sqlite, you just run rake db:migrate, however with pg you need to create the pg database first. Ryan did not do this step. The command is rake db:create:all, then we can run rake db:migrate

The second part is changing the database.yml file. The default for the username when the file is generated is 'appname'. However, chances are your role for postgresql admin is something different (at least it was for me). I changed it to my name (see above advice about creating a role name) and I was good to go.

Hope this helps.

PostgreSQL Error: Relation already exists

Another reason why you might get errors like "relation already exists" is if the DROP command did not execute correctly.

One reason this can happen is if there are other sessions connected to the database which you need to close first.

Reset auto increment counter in postgres

If you have a table with an IDENTITY column that you want to reset the next value for you can use the following command:

ALTER TABLE <table name> 
    ALTER COLUMN <column name> 
        RESTART WITH <new value to restart with>;

Postgresql query between date ranges

From PostreSQL 9.2 Range Types are supported. So you can write this like:

SELECT user_id
FROM user_logs
WHERE '[2014-02-01, 2014-03-01]'::daterange @> login_date

this should be more efficient than the string comparison

postgresql return 0 if returned value is null

I can think of 2 ways to achieve this:

  • IFNULL():

    The IFNULL() function returns a specified value if the expression is NULL.If the expression is NOT NULL, this function returns the expression.

Syntax:

IFNULL(expression, alt_value)

Example of IFNULL() with your query:

SELECT AVG( price )
FROM(
      SELECT *, cume_dist() OVER ( ORDER BY price DESC ) FROM web_price_scan
      WHERE listing_Type = 'AARM'
        AND u_kbalikepartnumbers_id = 1000307
        AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
        AND IFNULL( price, 0 ) > ( SELECT AVG( IFNULL( price, 0 ) )* 0.50
                                     FROM ( SELECT *, cume_dist() OVER ( ORDER BY price DESC )
                                           FROM web_price_scan
                                           WHERE listing_Type='AARM'
                                             AND u_kbalikepartnumbers_id = 1000307
                                             AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
                                         ) g
                                    WHERE cume_dist < 0.50
                                  )
        AND IFNULL( price, 0 ) < ( SELECT AVG( IFNULL( price, 0 ) ) *2
                                     FROM( SELECT *, cume_dist() OVER ( ORDER BY price desc )
                                           FROM web_price_scan
                                           WHERE listing_Type='AARM'
                                             AND u_kbalikepartnumbers_id = 1000307
                                             AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
                                         ) d
                                     WHERE cume_dist < 0.50)
     )s
HAVING COUNT(*) > 5
  • COALESCE()

    The COALESCE() function returns the first non-null value in a list.

Syntax:

COALESCE(val1, val2, ...., val_n)

Example of COALESCE() with your query:

SELECT AVG( price )
FROM(
      SELECT *, cume_dist() OVER ( ORDER BY price DESC ) FROM web_price_scan
      WHERE listing_Type = 'AARM'
        AND u_kbalikepartnumbers_id = 1000307
        AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
        AND COALESCE( price, 0 ) > ( SELECT AVG( COALESCE( price, 0 ) )* 0.50
                                     FROM ( SELECT *, cume_dist() OVER ( ORDER BY price DESC )
                                           FROM web_price_scan
                                           WHERE listing_Type='AARM'
                                             AND u_kbalikepartnumbers_id = 1000307
                                             AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
                                         ) g
                                    WHERE cume_dist < 0.50
                                  )
        AND COALESCE( price, 0 ) < ( SELECT AVG( COALESCE( price, 0 ) ) *2
                                     FROM( SELECT *, cume_dist() OVER ( ORDER BY price desc )
                                           FROM web_price_scan
                                           WHERE listing_Type='AARM'
                                             AND u_kbalikepartnumbers_id = 1000307
                                             AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
                                         ) d
                                     WHERE cume_dist < 0.50)
     )s
HAVING COUNT(*) > 5

updating table rows in postgres using subquery

Postgres allows:

UPDATE dummy
SET customer=subquery.customer,
    address=subquery.address,
    partn=subquery.partn
FROM (SELECT address_id, customer, address, partn
      FROM  /* big hairy SQL */ ...) AS subquery
WHERE dummy.address_id=subquery.address_id;

This syntax is not standard SQL, but it is much more convenient for this type of query than standard SQL. I believe Oracle (at least) accepts something similar.

How to UPSERT (MERGE, INSERT ... ON DUPLICATE UPDATE) in PostgreSQL?

I am trying to contribute with another solution for the single insertion problem with the pre-9.5 versions of PostgreSQL. The idea is simply to try to perform first the insertion, and in case the record is already present, to update it:

do $$
begin 
  insert into testtable(id, somedata) values(2,'Joe');
exception when unique_violation then
  update testtable set somedata = 'Joe' where id = 2;
end $$;

Note that this solution can be applied only if there are no deletions of rows of the table.

I do not know about the efficiency of this solution, but it seems to me reasonable enough.

proper hibernate annotation for byte[]

Thanks Justin, Pascal for guiding me to the right direction. I was also facing the same issue with Hibernate 3.5.3. Your research and pointers to the right classes had helped me identify the issue and do a fix.

For the benefit for those who are still stuck with Hibernate 3.5 and using oid + byte[] + @LoB combination, following is what I have done to fix the issue.

  1. I created a custom BlobType extending MaterializedBlobType and overriding the set and the get methods with the oid style access.

    public class CustomBlobType extends MaterializedBlobType {
    
    private static final String POSTGRESQL_DIALECT = PostgreSQLDialect.class.getName();
    
    /**
     * Currently set dialect.
     */
    private String dialect = hibernateConfiguration.getProperty(Environment.DIALECT);
    
    /*
     * (non-Javadoc)
     * @see org.hibernate.type.AbstractBynaryType#set(java.sql.PreparedStatement, java.lang.Object, int)
     */
    @Override
    public void set(PreparedStatement st, Object value, int index) throws HibernateException, SQLException {
        byte[] internalValue = toInternalFormat(value);
    
        if (POSTGRESQL_DIALECT.equals(dialect)) {
            try {
    
    //I had access to sessionFactory through a custom sessionFactory wrapper.
    st.setBlob(index, Hibernate.createBlob(internalValue, sessionFactory.getCurrentSession()));
                } catch (SystemException e) {
                    throw new HibernateException(e);
                }
            } else {
                st.setBytes(index, internalValue);
            }
        }
    
    /*
     * (non-Javadoc)
     * @see org.hibernate.type.AbstractBynaryType#get(java.sql.ResultSet, java.lang.String)
     */
    @Override
    public Object get(ResultSet rs, String name) throws HibernateException, SQLException {
        Blob blob = rs.getBlob(name);
        if (rs.wasNull()) {
            return null;
        }
        int length = (int) blob.length();
        return toExternalFormat(blob.getBytes(1, length));
      }
    }
    
    1. Register the CustomBlobType with Hibernate. Following is what i did to achieve that.

      hibernateConfiguration= new AnnotationConfiguration();
      Mappings mappings = hibernateConfiguration.createMappings();
      mappings.addTypeDef("materialized_blob", "x.y.z.BlobType", null);
      

Getting results between two dates in PostgreSQL

To have a query working in any locale settings, consider formatting the date yourself:

SELECT * 
  FROM testbed 
 WHERE start_date >= to_date('2012-01-01','YYYY-MM-DD')
   AND end_date <= to_date('2012-04-13','YYYY-MM-DD');

SQL LIKE condition to check for integer?

PostgreSQL supports regular expressions matching.

So, your example would look like

SELECT * FROM books WHERE title ~ '^\d+ ?' 

This will match a title starting with one or more digits and an optional space

How to log PostgreSQL queries?

You should also set this parameter to log every statement:

log_min_duration_statement = 0

How to select id with max date group by category in PostgreSQL?

This is a perfect use-case for DISTINCT ON - a Postgres specific extension of the standard DISTINCT:

SELECT DISTINCT ON (category)
       id  -- , category, date  -- any other column (expression) from the same row
FROM   tbl
ORDER  BY category, date DESC;

Careful with descending sort order. If the column can be NULL, you may want to add NULLS LAST:

DISTINCT ON is simple and fast. Detailed explanation in this related answer:

For big tables with many rows per category consider an alternative approach:

PostgreSQL 'NOT IN' and subquery

When using NOT IN, you should also consider NOT EXISTS, which handles the null cases silently. See also PostgreSQL Wiki

SELECT mac, creation_date 
FROM logs lo
WHERE logs_type_id=11
AND NOT EXISTS (
  SELECT *
  FROM consols nx
  WHERE nx.mac = lo.mac
  );

postgresql - add boolean column to table set default

ALTER TABLE users
  ADD COLUMN "priv_user" BOOLEAN DEFAULT FALSE;

you can also directly specify NOT NULL

ALTER TABLE users
  ADD COLUMN "priv_user" BOOLEAN NOT NULL DEFAULT FALSE;

UPDATE: following is only true for versions before postgresql 11.

As Craig mentioned on filled tables it is more efficient to split it into steps:

ALTER TABLE users ADD COLUMN priv_user BOOLEAN;
UPDATE users SET priv_user = 'f';
ALTER TABLE users ALTER COLUMN priv_user SET NOT NULL;
ALTER TABLE users ALTER COLUMN priv_user SET DEFAULT FALSE;

typecast string to integer - Postgres

If the value contains non-numeric characters, you can convert the value to an integer as follows:

SELECT CASE WHEN <column>~E'^\\d+$' THEN CAST (<column> AS INTEGER) ELSE 0 END FROM table;

The CASE operator checks the < column>, if it matches the integer pattern, it converts the rate into an integer, otherwise it returns 0

How to reset sequence in postgres and fill id column with new data?

Just resetting the sequence and updating all rows may cause duplicate id errors. In many cases you have to update all rows twice. First with higher ids to avoid the duplicates, then with the ids you actually want.

Please avoid to add a fixed amount to all ids (as recommended in other comments). What happens if you have more rows than this fixed amount? Assuming the next value of the sequence is higher than all the ids of the existing rows (you just want to fill the gaps), i would do it like:

UPDATE table SET id = DEFAULT;
ALTER SEQUENCE seq RESTART;
UPDATE table SET id = DEFAULT;

Return zero if no record is found

I'm not familiar with postgresql, but in SQL Server or Oracle, using a subquery would work like below (in Oracle, the SELECT 0 would be SELECT 0 FROM DUAL)

SELECT SUM(sub.value)
FROM
( 
  SELECT SUM(columnA) as value FROM my_table
  WHERE columnB = 1
  UNION
  SELECT 0 as value
) sub

Maybe this would work for postgresql too?

How to alter a column's data type in a PostgreSQL table?

Cool @derek-kromm, Your answer is accepted and correct, But I am wondering if we need to alter more than the column. Here is how we can do.

ALTER TABLE tbl_name 
ALTER COLUMN col_name TYPE varchar (11), 
ALTER COLUMN col_name2 TYPE varchar (11),
ALTER COLUMN col_name3 TYPE varchar (11);

Documentation

Cheers!! Read Simple Write Simple

How to export table as CSV with headings on Postgresql?

instead of just table name, you can also write a query for getting only selected column data.

COPY (select id,name from tablename) TO 'filepath/aa.csv' DELIMITER ',' CSV HEADER;

with admin privilege

\COPY (select id,name from tablename) TO 'filepath/aa.csv' DELIMITER ',' CSV HEADER;

How do you find the row count for all your tables in Postgres

If you're in the psql shell, using \gexec allows you to execute the syntax described in syed's answer and Aur's answer without manual edits in an external text editor.

with x (y) as (
    select
        'select count(*), '''||
        tablename||
        ''' as "tablename" from '||
        tablename||' '
    from pg_tables
    where schemaname='public'
)
select
    string_agg(y,' union all '||chr(10)) || ' order by tablename'
from x \gexec

Note, string_agg() is used both to delimit union all between statements and to smush the separated datarows into a single unit to be passed into the buffer.

\gexec

Sends the current query buffer to the server, then treats each column of each row of the query's output (if any) as a SQL statement to be executed.

How to get a value from the last inserted row?

Don't use SELECT currval('MySequence') - the value gets incremented on inserts that fail.

How to configure postgresql for the first time?

This is my solution:

su root
su postgres
psql

Where are my postgres *.conf files?

Run

sudo updatedb

followed by

locate postgresql.conf

How do I import modules or install extensions in PostgreSQL 9.1+?

In addition to the extensions which are maintained and provided by the core PostgreSQL development team, there are extensions available from third parties. Notably, there is a site dedicated to that purpose: http://www.pgxn.org/

How to check if a table exists in a given schema

Perhaps use information_schema:

SELECT EXISTS(
    SELECT * 
    FROM information_schema.tables 
    WHERE 
      table_schema = 'company3' AND 
      table_name = 'tableincompany3schema'
);

Find difference between timestamps in seconds in PostgreSQL

SELECT (cast(timestamp_1 as bigint) - cast(timestamp_2 as bigint)) FROM table;

In case if someone is having an issue using extract.

PostgreSQL: Which version of PostgreSQL am I running?

If Select version() returns with Memo try using the command this way:

Select version::char(100) 

or

Select version::varchar(100)

How to change owner of PostgreSql database?

ALTER DATABASE name OWNER TO new_owner;

See the Postgresql manual's entry on this for more details.

Combine two columns and add into one new column

You don't need to store the column to reference it that way. Try this:

To set up:

CREATE TABLE tbl
  (zipcode text NOT NULL, city text NOT NULL, state text NOT NULL);
INSERT INTO tbl VALUES ('10954', 'Nanuet', 'NY');

We can see we have "the right stuff":

\pset border 2
SELECT * FROM tbl;
+---------+--------+-------+
| zipcode |  city  | state |
+---------+--------+-------+
| 10954   | Nanuet | NY    |
+---------+--------+-------+

Now add a function with the desired "column name" which takes the record type of the table as its only parameter:

CREATE FUNCTION combined(rec tbl)
  RETURNS text
  LANGUAGE SQL
AS $$
  SELECT $1.zipcode || ' - ' || $1.city || ', ' || $1.state;
$$;

This creates a function which can be used as if it were a column of the table, as long as the table name or alias is specified, like this:

SELECT *, tbl.combined FROM tbl;

Which displays like this:

+---------+--------+-------+--------------------+
| zipcode |  city  | state |      combined      |
+---------+--------+-------+--------------------+
| 10954   | Nanuet | NY    | 10954 - Nanuet, NY |
+---------+--------+-------+--------------------+

This works because PostgreSQL checks first for an actual column, but if one is not found, and the identifier is qualified with a relation name or alias, it looks for a function like the above, and runs it with the row as its argument, returning the result as if it were a column. You can even index on such a "generated column" if you want to do so.

Because you're not using extra space in each row for the duplicated data, or firing triggers on all inserts and updates, this can often be faster than the alternatives.

Postgresql: error "must be owner of relation" when changing a owner object

Thanks to Mike's comment, I've re-read the doc and I've realised that my current user (i.e. userA that already has the create privilege) wasn't a direct/indirect member of the new owning role...

So the solution was quite simple - I've just done this grant:

grant userB to userA;

That's all folks ;-)


Update:

Another requirement is that the object has to be owned by user userA before altering it...

An URL to a Windows shared folder

If you are allowed to go further then javascript/html facilities - I would use the apache web server to represent your directory listing via http.

If this solution is appropriate. these are the steps:

  1. download apache hhtp server from one of the mirrors http://httpd.apache.org/download.cgi

  2. unzip/install (if msi) it to the directory e.g C:\opt\Apache (the instruction is for windows)

  3. map the network forlder as a local drive on windows (\server\folder to let's say drive H:)

  4. open conf/httpd.conf file

  5. make sure the next line is present and not commented

    LoadModule autoindex_module modules/mod_autoindex.so

  6. Add directory configuration

<Directory "H:/path">

Options +Indexes

AllowOverride None

Order allow,deny

Allow from all

</Directory> 7. Start the web server and make sure the directory listingof the remote folder is available by http. hit localhost/path 8. use a frame inside your web page to access the listing

What is missed: 1. you mignt need more fancy configuration for the host name, refer to Apache Web Server docs. Register the host name in DNS server

  1. the mapping to the network drive might not work, i did not check. As a posible resolution - host your web server on the same machine as smb server.

Find the closest ancestor element that has a specific class

@rvighne solution works well, but as identified in the comments ParentElement and ClassList both have compatibility issues. To make it more compatible, I have used:

function findAncestor (el, cls) {
    while ((el = el.parentNode) && el.className.indexOf(cls) < 0);
    return el;
}
  • parentNode property instead of the parentElement property
  • indexOf method on the className property instead of the contains method on the classList property.

Of course, indexOf is simply looking for the presence of that string, it does not care if it is the whole string or not. So if you had another element with class 'ancestor-type' it would still return as having found 'ancestor', if this is a problem for you, perhaps you can use regexp to find an exact match.

Pass multiple complex objects to a post/put Web API method

Basically you can send complex object without doing any extra fancy thing. Or without making changes to Web-Api. I mean why would we have to make changes to Web-Api, while the fault is in our code that's calling the Web-Api.

All you have to do use NewtonSoft's Json library as following.

string jsonObjectA = JsonConvert.SerializeObject(objectA);
string jsonObjectB = JsonConvert.SerializeObject(objectB);
string jSoNToPost = string.Format("\"content\": {0},\"config\":\"{1}\"",jsonObjectA , jsonObjectB );
//wrap it around in object container notation
jSoNToPost = string.Concat("{", jSoNToPost , "}"); 
//convert it to JSON acceptible content
HttpContent content = new StringContent(jSoNToPost , Encoding.UTF8, "application/json"); 

var response = httpClient.PutAsync("api/process/StartProcessiong", content);

test if display = none

Try this instead to only select the visible elements under the tbody:

$('tbody :visible').highlight(myArray[i]);

How can I set a proxy server for gem?

You need to add http_proxy and https_proxy environment variables as described here.

Rebuild all indexes in a Database

Also a good script, although my laptop ran out of memory, but this was on a very large table

https://basitaalishan.com/2014/02/23/rebuild-all-indexes-on-all-tables-in-the-sql-server-database/

USE [<mydatabasename>]
Go

--/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
--Arguments             Data Type               Description
--------------          ------------            ------------
--@FillFactor           [int]                   Specifies a percentage that indicates how full the Database Engine should make the leaf level
--                                              of each index page during index creation or alteration. The valid inputs for this parameter
--                                              must be an integer value from 1 to 100 The default is 0.
--                                              For more information, see http://technet.microsoft.com/en-us/library/ms177459.aspx.

--@PadIndex             [varchar](3)            Specifies index padding. The PAD_INDEX option is useful only when FILLFACTOR is specified,
--                                              because PAD_INDEX uses the percentage specified by FILLFACTOR. If the percentage specified
--                                              for FILLFACTOR is not large enough to allow for one row, the Database Engine internally
--                                              overrides the percentage to allow for the minimum. The number of rows on an intermediate
--                                              index page is never less than two, regardless of how low the value of fillfactor. The valid
--                                              inputs for this parameter are ON or OFF. The default is OFF.
--                                              For more information, see http://technet.microsoft.com/en-us/library/ms188783.aspx.

--@SortInTempDB         [varchar](3)            Specifies whether to store temporary sort results in tempdb. The valid inputs for this
--                                              parameter are ON or OFF. The default is OFF.
--                                              For more information, see http://technet.microsoft.com/en-us/library/ms188281.aspx.

--@OnlineRebuild        [varchar](3)            Specifies whether underlying tables and associated indexes are available for queries and data
--                                              modification during the index operation. The valid inputs for this parameter are ON or OFF.
--                                              The default is OFF.
--                                              Note: Online index operations are only available in Enterprise edition of Microsoft
--                                                      SQL Server 2005 and above.
--                                              For more information, see http://technet.microsoft.com/en-us/library/ms191261.aspx.

--@DataCompression      [varchar](4)            Specifies the data compression option for the specified index, partition number, or range of
--                                              partitions. The options  for this parameter are as follows:
--                                                  > NONE - Index or specified partitions are not compressed.
--                                                  > ROW  - Index or specified partitions are compressed by using row compression.
--                                                  > PAGE - Index or specified partitions are compressed by using page compression.
--                                              The default is NONE.
--                                              Note: Data compression feature is only available in Enterprise edition of Microsoft
--                                                      SQL Server 2005 and above.
--                                              For more information about compression, see http://technet.microsoft.com/en-us/library/cc280449.aspx.

--@MaxDOP               [int]                   Overrides the max degree of parallelism configuration option for the duration of the index
--                                              operation. The valid input for this parameter can be between 0 and 64, but should not exceed
--                                              number of processors available to SQL Server.
--                                              For more information, see http://technet.microsoft.com/en-us/library/ms189094.aspx.
--- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/

-- Ensure a USE <databasename> statement has been executed first.

SET NOCOUNT ON;

DECLARE  @Version                           [numeric] (18, 10)
        ,@SQLStatementID                    [int]
        ,@CurrentTSQLToExecute              [nvarchar](max)
        ,@FillFactor                        [int]        = 100 -- Change if needed
        ,@PadIndex                          [varchar](3) = N'OFF' -- Change if needed
        ,@SortInTempDB                      [varchar](3) = N'OFF' -- Change if needed
        ,@OnlineRebuild                     [varchar](3) = N'OFF' -- Change if needed
        ,@LOBCompaction                     [varchar](3) = N'ON' -- Change if needed
        ,@DataCompression                   [varchar](4) = N'NONE' -- Change if needed
        ,@MaxDOP                            [int]        = NULL -- Change if needed
        ,@IncludeDataCompressionArgument    [char](1);

IF OBJECT_ID(N'TempDb.dbo.#Work_To_Do') IS NOT NULL
    DROP TABLE #Work_To_Do
CREATE TABLE #Work_To_Do
    (
      [sql_id] [int] IDENTITY(1, 1)
                     PRIMARY KEY ,
      [tsql_text] [varchar](1024) ,
      [completed] [bit]
    )

SET @Version = CAST(LEFT(CAST(SERVERPROPERTY(N'ProductVersion') AS [nvarchar](128)), CHARINDEX('.', CAST(SERVERPROPERTY(N'ProductVersion') AS [nvarchar](128))) - 1) + N'.' + REPLACE(RIGHT(CAST(SERVERPROPERTY(N'ProductVersion') AS [nvarchar](128)), LEN(CAST(SERVERPROPERTY(N'ProductVersion') AS [nvarchar](128))) - CHARINDEX('.', CAST(SERVERPROPERTY(N'ProductVersion') AS [nvarchar](128)))), N'.', N'') AS [numeric](18, 10))

IF @DataCompression IN (N'PAGE', N'ROW', N'NONE')
    AND (
        @Version >= 10.0
        AND SERVERPROPERTY(N'EngineEdition') = 3
        )
BEGIN
    SET @IncludeDataCompressionArgument = N'Y'
END

IF @IncludeDataCompressionArgument IS NULL
BEGIN
    SET @IncludeDataCompressionArgument = N'N'
END

INSERT INTO #Work_To_Do ([tsql_text], [completed])
SELECT 'ALTER INDEX [' + i.[name] + '] ON' + SPACE(1) + QUOTENAME(t2.[TABLE_CATALOG]) + '.' + QUOTENAME(t2.[TABLE_SCHEMA]) + '.' + QUOTENAME(t2.[TABLE_NAME]) + SPACE(1) + 'REBUILD WITH (' + SPACE(1) + + CASE
        WHEN @PadIndex IS NULL
            THEN 'PAD_INDEX =' + SPACE(1) + CASE i.[is_padded]
                    WHEN 1
                        THEN 'ON'
                    WHEN 0
                        THEN 'OFF'
                    END
        ELSE 'PAD_INDEX =' + SPACE(1) + @PadIndex
        END + CASE
        WHEN @FillFactor IS NULL
            THEN ', FILLFACTOR =' + SPACE(1) + CONVERT([varchar](3), REPLACE(i.[fill_factor], 0, 100))
        ELSE ', FILLFACTOR =' + SPACE(1) + CONVERT([varchar](3), @FillFactor)
        END + CASE
        WHEN @SortInTempDB IS NULL
            THEN ''
        ELSE ', SORT_IN_TEMPDB =' + SPACE(1) + @SortInTempDB
        END + CASE
        WHEN @OnlineRebuild IS NULL
            THEN ''
        ELSE ', ONLINE =' + SPACE(1) + @OnlineRebuild
        END + ', STATISTICS_NORECOMPUTE =' + SPACE(1) + CASE st.[no_recompute]
        WHEN 0
            THEN 'OFF'
        WHEN 1
            THEN 'ON'
        END + ', ALLOW_ROW_LOCKS =' + SPACE(1) + CASE i.[allow_row_locks]
        WHEN 0
            THEN 'OFF'
        WHEN 1
            THEN 'ON'
        END + ', ALLOW_PAGE_LOCKS =' + SPACE(1) + CASE i.[allow_page_locks]
        WHEN 0
            THEN 'OFF'
        WHEN 1
            THEN 'ON'
        END + CASE
        WHEN @IncludeDataCompressionArgument = N'Y'
            THEN CASE
                    WHEN @DataCompression IS NULL
                        THEN ''
                    ELSE ', DATA_COMPRESSION =' + SPACE(1) + @DataCompression
                    END
        ELSE ''
        END + CASE
        WHEN @MaxDop IS NULL
            THEN ''
        ELSE ', MAXDOP =' + SPACE(1) + CONVERT([varchar](2), @MaxDOP)
        END + SPACE(1) + ')'
    ,0
FROM [sys].[tables] t1
INNER JOIN [sys].[indexes] i ON t1.[object_id] = i.[object_id]
    AND i.[index_id] > 0
    AND i.[type] IN (1, 2)
INNER JOIN [INFORMATION_SCHEMA].[TABLES] t2 ON t1.[name] = t2.[TABLE_NAME]
    AND t2.[TABLE_TYPE] = 'BASE TABLE'
INNER JOIN [sys].[stats] AS st WITH (NOLOCK) ON st.[object_id] = t1.[object_id]
    AND st.[name] = i.[name]

SELECT @SQLStatementID = MIN([sql_id])
FROM #Work_To_Do
WHERE [completed] = 0

WHILE @SQLStatementID IS NOT NULL
BEGIN
    SELECT @CurrentTSQLToExecute = [tsql_text]
    FROM #Work_To_Do
    WHERE [sql_id] = @SQLStatementID

    PRINT @CurrentTSQLToExecute

    EXEC [sys].[sp_executesql] @CurrentTSQLToExecute

    UPDATE #Work_To_Do
    SET [completed] = 1
    WHERE [sql_id] = @SQLStatementID

    SELECT @SQLStatementID = MIN([sql_id])
    FROM #Work_To_Do
    WHERE [completed] = 0
END

How to use git merge --squash?

if you get error: Committing is not possible because you have unmerged files.

git checkout master
git merge --squash bugfix
git add .
git commit -m "Message"

fixed all the Conflict files

git add . 

you could also use

git add [filename]

Label encoding across multiple columns in scikit-learn

Using Neuraxle

TLDR; You here can use the FlattenForEach wrapper class to simply transform your df like: FlattenForEach(LabelEncoder(), then_unflatten=True).fit_transform(df).

With this method, your label encoder will be able to fit and transform within a regular scikit-learn Pipeline. Let's simply import:

from sklearn.preprocessing import LabelEncoder
from neuraxle.steps.column_transformer import ColumnTransformer
from neuraxle.steps.loop import FlattenForEach

Same shared encoder for columns:

Here is how one shared LabelEncoder will be applied on all the data to encode it:

    p = FlattenForEach(LabelEncoder(), then_unflatten=True)

Result:

    p, predicted_output = p.fit_transform(df.values)
    expected_output = np.array([
        [6, 7, 6, 8, 7, 7],
        [1, 3, 0, 1, 5, 3],
        [4, 2, 2, 4, 4, 2]
    ]).transpose()
    assert np.array_equal(predicted_output, expected_output)

Different encoders per column:

And here is how a first standalone LabelEncoder will be applied on the pets, and a second will be shared for the columns owner and location. So to be precise, we here have a mix of different and shared label encoders:

    p = ColumnTransformer([
        # A different encoder will be used for column 0 with name "pets":
        (0, FlattenForEach(LabelEncoder(), then_unflatten=True)),
        # A shared encoder will be used for column 1 and 2, "owner" and "location":
        ([1, 2], FlattenForEach(LabelEncoder(), then_unflatten=True)),
    ], n_dimension=2)

Result:

    p, predicted_output = p.fit_transform(df.values)
    expected_output = np.array([
        [0, 1, 0, 2, 1, 1],
        [1, 3, 0, 1, 5, 3],
        [4, 2, 2, 4, 4, 2]
    ]).transpose()
    assert np.array_equal(predicted_output, expected_output)

How to efficiently change image attribute "src" from relative URL to absolute using jQuery?

The replace method in Javascript returns a value, and does not act upon the existing string object. See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace

In your example, you will have to do

$(this).attr("src", $(this).attr("src").replace(...))

What is REST? Slightly confused

REST is not a specific web service but a design concept (architecture) for managing state information. The seminal paper on this was Roy Thomas Fielding's dissertation (2000), "Architectural Styles and the Design of Network-based Software Architectures" (available online from the University of California, Irvine).

First read Ryan Tomayko's post How I explained REST to my wife; it's a great starting point. Then read Fielding's actual dissertation. It's not that advanced, nor is it long (six chapters, 180 pages)! (I know you kids in school like it short).

EDIT: I feel it's pointless to try to explain REST. It has so many concepts like scalability, visibility (stateless) etc. that the reader needs to grasp, and the best source for understanding those are the actual dissertation. It's much more than POST/GET etc.

CSS: auto height on containing div, 100% height on background div inside containing div

Somewhere you will need to set a fixed height, instead of using auto everywhere. You will find that if you set a fixed height on your content and/or container, then using auto for things inside it will work.

Also, your boxes will still expand height-wise with more content in, even though you have set a height for it - so don't worry about that :)

#container {
  height:500px;
  min-height:500px;
}

How to recompile with -fPIC

Have a look at this page.

you can try globally adding the flag using: export CXXFLAGS="$CXXFLAGS -fPIC"

Disable eslint rules for folder

The previous answers were in the right track, but the complete answer for this is going to Disabling rules only for a group of files, there you'll find the documentation needed to disable/enable rules for certain folders (Because in some cases you don't want to ignore the whole thing, only disable certain rules). Example:

{
    "env": {},
    "extends": [],
    "parser": "",
    "plugins": [],
    "rules": {},
    "overrides": [
      {
        "files": ["test/*.spec.js"], // Or *.test.js
        "rules": {
          "require-jsdoc": "off"
        }
      }
    ],
    "settings": {}
}

How to recover a dropped stash in Git?

I liked Aristotle's approach, but didn't like using GITK... as I'm used to using GIT from the command line.

Instead, I took the dangling commits and output the code to a DIFF file for review in my code editor.

git show $( git fsck --no-reflog | awk '/dangling commit/ {print $3}' ) > ~/stash_recovery.diff

Now you can load up the resulting diff/txt file (its in your home folder) into your txt editor and see the actual code and resulting SHA.

Then just use

git stash apply ad38abbf76e26c803b27a6079348192d32f52219

how to have two headings on the same line in html

You'd need to wrap the two headings in a div tag, and have that div tag use a style that does clear: both. e.g:

<div style="clear: both">
    <h2 style="float: left">Heading 1</h2>
    <h3 style="float: right">Heading 2</h3>
</div>
<hr />

Having the hr after the div tag will ensure that it is pushed beneath both headers.

Or something very similar to that. Hope this helps.

Take a full page screenshot with Firefox on the command-line

Firefox Screenshots is a new tool that ships with Firefox. It is not a developer tool, it is aimed at end-users of the browser.

To take a screenshot, click on the page actions menu in the address bar, and click "take a screenshot". If you then click "Save full page", it will save the full page, scrolling for you.


(source: mozilla.net)

Directly export a query to CSV using SQL Developer

You can use the spool command (SQL*Plus documentation, but one of many such commands SQL Developer also supports) to write results straight to disk. Each spool can change the file that's being written to, so you can have several queries writing to different files just by putting spool commands between them:

spool "\path\to\spool1.txt"

select /*csv*/ * from employees;

spool "\path\to\spool2.txt"

select /*csv*/ * from locations;

spool off;

You'd need to run this as a script (F5, or the second button on the command bar above the SQL Worksheet). You might also want to explore some of the formatting options and the set command, though some of those do not translate to SQL Developer.

Since you mentioned CSV in the title I've included a SQL Developer-specific hint that does that formatting for you.

A downside though is that SQL Developer includes the query in the spool file, which you can avoid by having the commands and queries in a script file that you then run as a script.

How to sort by Date with DataTables jquery plugin?

Follow the link https://datatables.net/blog/2014-12-18

A very easy way to integrate ordering by date.

<script type="text/javascript" charset="utf8" src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.8.4/moment.min.js"></script>
<script type="text/javascript" charset="utf8" src="https://cdn.datatables.net/plug-ins/1.10.19/sorting/datetime-moment.js"></script>

Put this code in before initializing the datatable:

$(document).ready(function () {
    // ......
    $.fn.dataTable.moment('DD-MMM-YY HH:mm:ss');
    $.fn.dataTable.moment('DD.MM.YYYY HH:mm:ss');
    // And any format you need
}

Assign multiple values to array in C

Although in your case, just plain initialization will do, there's a trick to wrap the array into a struct (which can be initialized after declaration).

For example:

struct foo {
  GLfloat arr[10];
};
...
struct foo foo;
foo = (struct foo) { .arr = {1.0, ... } };

Open youtube video in Fancybox jquery

This has a regular expression so it's easier to just copy and paste the youtube url. Is great for when you use a CMS for clients.

/*fancybox yt video*/
$(".fancybox-video").click(function() {
    $.fancybox({

    padding: 0,
        'autoScale'     : false,
        'transitionIn'  : 'none',
        'transitionOut' : 'none',
        'title'         : this.title,
        'width'         : 795,
        'height'        : 447,
        'href'          : this.href.replace(new RegExp("watch.*v=","i"), "v/"),
        'type'          : 'swf',
        'swf'           : {
        'wmode'             : 'transparent',
        'allowfullscreen'   : 'true'
         }

    });
    return false;
});

Handling Dialogs in WPF with MVVM

I was pondering a similar problem when asking how the view model for a task or dialog should look like.

My current solution looks like this:

public class SelectionTaskModel<TChoosable> : ViewModel
    where TChoosable : ViewModel
{
    public SelectionTaskModel(ICollection<TChoosable> choices);
    public ReadOnlyCollection<TChoosable> Choices { get; }
    public void Choose(TChoosable choosen);
    public void Abort();
}

When the view model decides that user input is required, it pulls up a instance of SelectionTaskModel with the possible choices for the user. The infrastructure takes care of bringing up the corresponding view, which in proper time will call the Choose() function with the user's choice.

Correct way to initialize empty slice

Empty slice and nil slice are initialized differently in Go:

var nilSlice []int 
emptySlice1 := make([]int, 0)
emptySlice2 := []int{}

fmt.Println(nilSlice == nil)    // true
fmt.Println(emptySlice1 == nil) // false
fmt.Println(emptySlice2 == nil) // false

As for all three slices, len and cap are 0.

Text File Parsing in Java

While calling/invoking your programme you can use this command : java [-options] className [args...]
in place of [-options] provide more memory e.g -Xmx1024m or more. but this is just a workaround, u have to change ur parsing mechanism.

String comparison: InvariantCultureIgnoreCase vs OrdinalIgnoreCase?

Neither code is always better. They do different things, so they are good at different things.

InvariantCultureIgnoreCase uses comparison rules based on english, but without any regional variations. This is good for a neutral comparison that still takes into account some linguistic aspects.

OrdinalIgnoreCase compares the character codes without cultural aspects. This is good for exact comparisons, like login names, but not for sorting strings with unusual characters like é or ö. This is also faster because there are no extra rules to apply before comparing.

R Apply() function on specific dataframe columns

I think what you want is mapply. You could apply the function to all columns, and then just drop the columns you don't want. However, if you are applying different functions to different columns, it seems likely what you want is mutate, from the dplyr package.

Why should I use a container div in HTML?

The most common reasons for me are so that:

  1. The layout can have a fixed width (yes, I know, I do a lot of work for designers who love fixed widths), and
  2. So the layout can be centered by applying text-align: center to the body and then margin: auto to the left and right of the container div.

Oracle - What TNS Names file am I using?

strace sqlplus -L scott/tiger@orcl helps to find .tnsnames.ora file on /home/oracle to find the file it takes instead of $ORACLE_HOME/network/admin/tnsnames.ora file. Thanks for the posting.

What's the difference between Docker Compose vs. Dockerfile

"better" is relative. It all depends on what your needs are. Docker compose is for orchestrating multiple containers. If these images already exist in the docker registry, then it's better to list them in the compose file. If these images or some other images have to be built from files on your computer, then you can describe the processes of building those images in a Dockerfile.

I understand that Dockerfiles are used in Docker Compose, but I am not sure if it is good practice to put everything in one large Dockerfile with multiple FROM commands for the different images?

Using multiple FROM in a single dockerfile is not a very good idea because there is a proposal to remove the feature. 13026

If for instance, you want to dockerize an application which uses a database and have the application files on your computer, you can use a compose file together with a dockerfile as follows

docker-compose.yml

mysql:
  image: mysql:5.7
  volumes:
    - ./db-data:/var/lib/mysql
  environment:
    - "MYSQL_ROOT_PASSWORD=secret"
    - "MYSQL_DATABASE=homestead"
    - "MYSQL_USER=homestead"
  ports:
    - "3307:3306"
app:
  build:
    context: ./path/to/Dockerfile
    dockerfile: Dockerfile
  volumes:
    - ./:/app
  working_dir: /app
      

Dockerfile

FROM php:7.1-fpm 
RUN apt-get update && apt-get install -y libmcrypt-dev \
  mysql-client libmagickwand-dev --no-install-recommends \
  && pecl install imagick \
  && docker-php-ext-enable imagick \
  && docker-php-ext-install pdo_mysql \
  && curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer

How do I directly modify a Google Chrome Extension File? (.CRX)

Now Chrome is multi-user so Extensions should be nested under the OS user profile then the Chrome user profile, My first Chrome user was called Profile 1, my Extensions path was C:\Users\ username \AppData\Local\Google\Chrome\User Data\ Profile 1 \Extensions\.

To find yours Navigate to chrome://version/ (I use about: out of laziness).

Notice the Profile Path and just append \Extensions\ and you have yours.

Hope this brings this info on this question up to date more.

Multiple select statements in Single query

SELECT  (
    SELECT COUNT(*)
    FROM   user_table
) AS tot_user,
(
    SELECT COUNT(*)
    FROM   cat_table
) AS tot_cat,
(
    SELECT COUNT(*)
    FROM   course_table
) AS tot_course

Print all day-dates between two dates

import datetime

begin = datetime.date(2008, 8, 15)
end = datetime.date(2008, 9, 15)

next_day = begin
while True:
    if next_day > end:
        break
    print next_day
    next_day += datetime.timedelta(days=1)

How do I get the key at a specific index from a Dictionary in Swift?

SWIFT 4


Slightly off-topic: But here is if you have an Array of Dictionaries i.e: [ [String : String] ]

var array_has_dictionary = [ // Start of array

   // Dictionary 1

   [ 
     "name" : "xxxx",
     "age" : "xxxx",
     "last_name":"xxx"
   ],

   // Dictionary 2

   [ 
     "name" : "yyy",
     "age" : "yyy",
     "last_name":"yyy"
   ],

 ] // end of array


cell.textLabel?.text =  Array(array_has_dictionary[1])[1].key
// Output: age -> yyy

Open multiple Projects/Folders in Visual Studio Code

It's not possible to open a new instance of Visual Studio Code normally, neither it works if you open the new one as Administrator.

Solution: simply right click on VS Code .exe file, and click "New Window" you can open as many new windows as you want. :)

Where are my postgres *.conf files?

For CentOS 6 and 7 and postgresql 9.2 (and below, I suppose, possibly Fedora and Redhat as well):

/var/lib/pgsql/data

For CentOS 6 and 7 postgresql 9.3 or 9.4 (and above, I suppose):

/var/lib/pgsql/9.3/data
/var/lib/pgsql/9.4/data

For Ubuntu 14 and postgresql 9.3:

/etc/postgresql/9.3/main/postgresql.conf

Calling startActivity() from outside of an Activity?

Try changing to this line:

PendingIntent pendingIntent = PendingIntent.getBroadcast(getContext(), 0, i, 0);

Error retrieving parent for item: No resource found that matches the given name after upgrading to AppCompat v23

Another solution : navigate to

\sdk\extras\android\m2repository\com\android\support\appcompat-v7\23.x.x

open .aar file with 7-zip or winrar , in res folder remove values-23 folder and save changes .

Get a list of resources from classpath directory

Custom Scanner

Implement your own scanner. For example:

(limitations of this solution are mentioned in the comments)

private List<String> getResourceFiles(String path) throws IOException {
    List<String> filenames = new ArrayList<>();

    try (
            InputStream in = getResourceAsStream(path);
            BufferedReader br = new BufferedReader(new InputStreamReader(in))) {
        String resource;

        while ((resource = br.readLine()) != null) {
            filenames.add(resource);
        }
    }

    return filenames;
}

private InputStream getResourceAsStream(String resource) {
    final InputStream in
            = getContextClassLoader().getResourceAsStream(resource);

    return in == null ? getClass().getResourceAsStream(resource) : in;
}

private ClassLoader getContextClassLoader() {
    return Thread.currentThread().getContextClassLoader();
}

Spring Framework

Use PathMatchingResourcePatternResolver from Spring Framework.

Ronmamo Reflections

The other techniques might be slow at runtime for huge CLASSPATH values. A faster solution is to use ronmamo's Reflections API, which precompiles the search at compile time.

How to make a GridLayout fit screen size

I archive this using LinearLayout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">
        <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:height="166dp"
            android:text="Tile1"
            android:gravity="center"
            android:background="#6f19e5"/>
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView
            android:text="Tile2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:height="126dp"
            android:gravity="center"
            android:layout_weight=".50"
            android:background="#f1d600"/>

        <TextView
            android:text="Tile3"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:height="126dp"
            android:gravity="center"
            android:layout_weight=".50"
            android:background="#e75548"/>

    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView
            android:text="Tile4"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:height="126dp"
            android:gravity="center"
            android:layout_weight=".50"
            android:background="#29d217"/>

        <TextView
            android:text="Tile5"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:height="126dp"
            android:gravity="center"
            android:layout_weight=".50"
            android:background="#e519cb"/>

    </LinearLayout>
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:height="176dp"
            android:text="Tile6"
            android:gravity="center"
            android:background="#09eadd"/>
    </LinearLayout>
</LinearLayout>

Here the modal

Django 1.7 - makemigrations not detecting changes

Had the same problem Make sure whatever classes you have defined in models.py, you must have to inherit models.Model class.

class Product(models.Model):
    title = models.TextField()
    description = models.TextField()
    price = models.TextField()

"unary operator expected" error in Bash if condition

You can also set a default value for the variable, so you don't need to use two "[", which amounts to two processes ("[" is actually a program) instead of one.

It goes by this syntax: ${VARIABLE:-default}.

The whole thing has to be thought in such a way that this "default" value is something distinct from a "valid" value/content.

If that's not possible for some reason you probably need to add a step like checking if there's a value at all, along the lines of "if [ -z $VARIABLE ] ; then echo "the variable needs to be filled"", or "if [ ! -z $VARIABLE ] ; then #everything is fine, proceed with the rest of the script".

How do I get the serial key for Visual Studio Express?

Visual C# Express 2005 ISO File does not require registration

How can I brew link a specific version?

brew switch libfoo mycopy

You can use brew switch to switch between versions of the same package, if it's installed as versioned subdirectories under Cellar/<packagename>/

This will list versions installed ( for example I had Cellar/sdl2/2.0.3, I've compiled into Cellar/sdl2/2.0.4)

brew info sdl2

Then to switch between them

brew switch sdl2 2.0.4
brew info 

Info now shows * next to the 2.0.4

To install under Cellar/<packagename>/<version> from source you can do for example

cd ~/somewhere/src/foo-2.0.4
./configure --prefix $(brew --Cellar)/foo/2.0.4
make

check where it gets installed with

make install -n

if all looks correct

make install

Then from cd $(brew --Cellar) do the switch between version.

I'm using brew version 0.9.5

Invert colors of an image in CSS or JavaScript

Can be done in major new broswers using the code below

.img {
    -webkit-filter:invert(100%);
     filter:progid:DXImageTransform.Microsoft.BasicImage(invert='1');
}

However, if you want it to work across all browsers you need to use Javascript. Something like this gist will do the job.

How can I multiply and divide using only bit shifting and adding?

  1. A left shift by 1 position is analogous to multiplying by 2. A right shift is analogous to dividing by 2.
  2. You can add in a loop to multiply. By picking the loop variable and the addition variable correctly, you can bound performance. Once you've explored that, you should use Peasant Multiplication

How to get ELMAH to work with ASP.NET MVC [HandleError] attribute?

You can take the code above and go one step further by introducing a custom controller factory that injects the HandleErrorWithElmah attribute into every controller.

For more infomation check out my blog series on logging in MVC. The first article covers getting Elmah set up and running for MVC.

There is a link to downloadable code at the end of the article. Hope that helps.

http://dotnetdarren.wordpress.com/

Upload DOC or PDF using PHP

You can use

$_FILES['filename']['error'];

If any type of error occurs then it returns 'error' else 1,2,3,4 or 1 if done

1 : if file size is over limit .... You can find other options by googling

What is the easiest way to remove all packages installed by pip?

Cross-platform support by using only pip:

#!/usr/bin/env python

from sys import stderr
from pip.commands.uninstall import UninstallCommand
from pip import get_installed_distributions

pip_uninstall = UninstallCommand()
options, args = pip_uninstall.parse_args([
    package.project_name
    for package in
    get_installed_distributions()
    if not package.location.endswith('dist-packages')
])

options.yes = True  # Don't confirm before uninstall
# set `options.require_venv` to True for virtualenv restriction

try:
    print pip_uninstall.run(options, args)
except OSError as e:
    if e.errno != 13:
        raise e
    print >> stderr, "You lack permissions to uninstall this package.
                      Perhaps run with sudo? Exiting."
    exit(13)
# Plenty of other exceptions can be thrown, e.g.: `InstallationError`
# handle them if you want to.

Delete/Reset all entries in Core Data?

You can still delete the file programmatically, using the NSFileManager:removeItemAtPath:: method.

NSPersistentStore *store = ...;
NSError *error;
NSURL *storeURL = store.URL;
NSPersistentStoreCoordinator *storeCoordinator = ...;
[storeCoordinator removePersistentStore:store error:&error];
[[NSFileManager defaultManager] removeItemAtPath:storeURL.path error:&error];

Then, just add the persistent store back to ensure it is recreated properly.

The programmatic way for iterating through each entity is both slower and prone to error. The use for doing it that way is if you want to delete some entities and not others. However you still need to make sure you retain referential integrity or you won't be able to persist your changes.

Just removing the store and recreating it is both fast and safe, and can certainly be done programatically at runtime.

Update for iOS5+

With the introduction of external binary storage (allowsExternalBinaryDataStorage or Store in External Record File) in iOS 5 and OS X 10.7, simply deleting files pointed by storeURLs is not enough. You'll leave the external record files behind. Since the naming scheme of these external record files is not public, I don't have a universal solution yet. – an0 May 8 '12 at 23:00

Javascript communication between browser tabs/windows

Communicating between different JavaScript execution context was supported even before HTML5 if the documents was of the same origin. If not or you have no reference to the other Window object, then you could use the new postMessage API introduced with HTML5. I elaborated a bit on both approaches in this stackoverflow answer.

How to add property to a class dynamically?

Extending the idea from kjfletch

# This is my humble contribution, extending the idea to serialize
# data from and to tuples, comparison operations and allowing functions
# as default values.

def Struct(*args, **kwargs):
    FUNCTIONS = (types.BuiltinFunctionType, types.BuiltinMethodType, \
                 types.FunctionType, types.MethodType)
    def init(self, *iargs, **ikwargs):
        """Asume that unamed args are placed in the same order than
        astuple() yields (currently alphabetic order)
        """
        kw = list(self.__slots__)

        # set the unnamed args
        for i in range(len(iargs)):
            k = kw.pop(0)
            setattr(self, k, iargs[i])

        # set the named args
        for k, v in ikwargs.items():
            setattr(self, k, v)
            kw.remove(k)

        # set default values
        for k in kw:
            v = kwargs[k]
            if isinstance(v, FUNCTIONS):
                v = v()
            setattr(self, k, v)

    def astuple(self):
        return tuple([getattr(self, k) for k in self.__slots__])

    def __str__(self):
        data = ['{}={}'.format(k, getattr(self, k)) for k in self.__slots__]
        return '<{}: {}>'.format(self.__class__.__name__, ', '.join(data))

    def __repr__(self):
        return str(self)

    def __eq__(self, other):
        return self.astuple() == other.astuple()

    name = kwargs.pop("__name__", "MyStruct")
    slots = list(args)
    slots.extend(kwargs.keys())
    # set non-specific default values to None
    kwargs.update(dict((k, None) for k in args))

    return type(name, (object,), {
        '__init__': init,
        '__slots__': tuple(slots),
        'astuple': astuple,
        '__str__': __str__,
        '__repr__': __repr__,
        '__eq__': __eq__,
    })


Event = Struct('user', 'cmd', \
               'arg1', 'arg2',  \
               date=time.time, \
               __name__='Event')

aa = Event('pepe', 77)
print(aa)
raw = aa.astuple()

bb = Event(*raw)
print(bb)

if aa == bb:
    print('Are equals')

cc = Event(cmd='foo')
print(cc)

Output:

<Event: user=pepe, cmd=77, arg1=None, arg2=None, date=1550051398.3651814>
<Event: user=pepe, cmd=77, arg1=None, arg2=None, date=1550051398.3651814>
Are equals
<Event: user=None, cmd=foo, arg1=None, arg2=None, date=1550051403.7938335>

Uncaught (in promise): Error: StaticInjectorError(AppModule)[options]

Here is what worked for me (Angular 7):

First import HttpClientModule in your app.module.ts if you didn't:

import { HttpClientModule } from '@angular/common/http';
...
imports: [
        HttpClientModule
    ],

Then change your service

@Injectable()
export class FooService {

to

@Injectable({
    providedIn: 'root'
})
export class FooService {

Hope it helps.

Edit:

providedIn

Determines which injectors will provide the injectable, by either associating it with an @NgModule or other InjectorType, or by specifying that this injectable should be provided in one of the following injectors:

'root' : The application-level injector in most apps.

'platform' : A special singleton platform injector shared by all applications on the page.

'any' : Provides a unique instance in every module (including lazy modules) that injects the token.

Be careful platform is available only since Angular 9 (https://blog.angular.io/version-9-of-angular-now-available-project-ivy-has-arrived-23c97b63cfa3)

Read more about Injectable here: https://angular.io/api/core/Injectable

Variables declared outside function

Unlike languages that employ 'true' lexical scoping, Python opts to have specific 'namespaces' for variables, whether it be global, nonlocal, or local. It could be argued that making developers consciously code with such namespaces in mind is more explicit, thus more understandable. I would argue that such complexities make the language more unwieldy, but I guess it's all down to personal preference.

Here are some examples regarding global:-

>>> global_var = 5
>>> def fn():
...     print(global_var)
... 
>>> fn()
5
>>> def fn_2():
...     global_var += 2
...     print(global_var)
... 
>>> fn_2()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in fn_2
UnboundLocalError: local variable 'global_var' referenced before assignment
>>> def fn_3():
...     global global_var
...     global_var += 2
...     print(global_var)
... 
>>> fn_3()
7

The same patterns can be applied to nonlocal variables too, but this keyword is only available to the latter Python versions.

In case you're wondering, nonlocal is used where a variable isn't global, but isn't within the function definition it's being used. For example, a def within a def, which is a common occurrence partially due to a lack of multi-statement lambdas. There's a hack to bypass the lack of this feature in the earlier Pythons though, I vaguely remember it involving the use of a single-element list...

Note that writing to variables is where these keywords are needed. Just reading from them isn't ambiguous, thus not needed. Unless you have inner defs using the same variable names as the outer ones, which just should just be avoided to be honest.

How to store a datetime in MySQL with timezone info

None of the answers here quite hit the nail on the head.

How to store a datetime in MySQL with timezone info

Use two columns: DATETIME, and a VARCHAR to hold the time zone information, which may be in several forms:

A timezone or location such as America/New_York is the highest data fidelity.

A timezone abbreviation such as PST is the next highest fidelity.

A time offset such as -2:00 is the smallest amount of data in this regard.

Some key points:

  • Avoid TIMESTAMP because it's limited to the year 2038, and MySQL relates it to the server timezone, which is probably undesired.
  • A time offset should not be stored naively in an INT field, because there are half-hour and quarter-hour offsets.

If it's important for your use case to have MySQL compare or sort these dates chronologically, DATETIME has a problem:

'2009-11-10 11:00:00 -0500' is before '2009-11-10 10:00:00 -0700' in terms of "instant in time", but they would sort the other way when inserted into a DATETIME.

You can do your own conversion to UTC. In the above example, you would then have
'2009-11-10 16:00:00' and '2009-11-10 17:00:00' respectively, which would sort correctly. When retrieving the data, you would then use the timezone info to revert it to its original form.

One recommendation which I quite like is to have three columns:

  • local_time DATETIME
  • utc_time DATETIME
  • time_zone VARCHAR(X) where X is appropriate for what kind of data you're storing there. (I would choose 64 characters for timezone/location.)

An advantage to the 3-column approach is that it's explicit: with a single DATETIME column, you can't tell at a glance if it's been converted to UTC before insertion.


Regarding the descent of accuracy through timezone/abbreviation/offset:

  • If you have the user's timezone/location such as America/Juneau, you can know accurately what the wall clock time is for them at any point in the past or future (barring changes to the way Daylight Savings is handled in that location). The start/end points of DST, and whether it's used at all, are dependent upon location, so this is the only reliable way.
  • If you have a timezone abbreviation such as MST, (Mountain Standard Time) or a plain offset such as -0700, you will be unable to predict a wall clock time in the past or future. For example, in the United States, Colorado and Arizona both use MST, but Arizona doesn't observe DST. So if the user uploads his cat photo at 14:00 -0700 during the winter months, was he in Arizona or California? If you added six months exactly to that date, would it be 14:00 or 13:00 for the user?

These things are important to consider when your application has time, dates, or scheduling as core function.


References:

Grid of responsive squares

Now we can easily do this using the aspect-ratio ref property

_x000D_
_x000D_
.container {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr)); /* 3 columns */
  grid-gap: 10px;
}

.container>* {
  aspect-ratio: 1 / 1; /* a square ratio */
  border: 1px solid;
  
  /* center content */
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
}

img {
  max-width: 100%;
  display: block;
}
_x000D_
<div class="container">
  <div> some content here </div>
  <div><img src="https://picsum.photos/id/25/400/400"></div>
  <div>
    <h1>a title</h1>
  </div>
  <div>more and more content <br>here</div>
  <div>
    <h2>another title</h2>
  </div>
  <div><img src="https://picsum.photos/id/104/400/400"></div>
</div>
_x000D_
_x000D_
_x000D_

Also like below where we can have a variable number of columns

_x000D_
_x000D_
.container {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  grid-gap: 10px;
}

.container>* {
  aspect-ratio: 1 / 1; /* a square ratio */
  border: 1px solid;
  
  /* center content */
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
}

img {
  max-width: 100%;
  display: block;
}
_x000D_
<div class="container">
  <div> some content here </div>
  <div><img src="https://picsum.photos/id/25/400/400"></div>
  <div>
    <h1>a title</h1>
  </div>
  <div>more and more content <br>here</div>
  <div>
    <h2>another title</h2>
  </div>
  <div><img src="https://picsum.photos/id/104/400/400"></div>
  <div>more and more content <br>here</div>
  <div>
    <h2>another title</h2>
  </div>
  <div><img src="https://picsum.photos/id/104/400/400"></div>
</div>
_x000D_
_x000D_
_x000D_

Error in <my code> : object of type 'closure' is not subsettable

In case of this similar error Warning: Error in $: object of type 'closure' is not subsettable [No stack trace available]

Just add corresponding package name using :: e.g.

instead of tags(....)

write shiny::tags(....)

How can I initialize a C# List in the same line I declare it. (IEnumerable string Collection Example)

Remove the parentheses:

List<string> nameslist = new List<string> {"one", "two", "three"};

Can functions be passed as parameters?

Here is the sample "Map" implementation in Go. Hope this helps!!

func square(num int) int {
    return num * num
}

func mapper(f func(int) int, alist []int) []int {
    var a = make([]int, len(alist), len(alist))
    for index, val := range alist {

        a[index] = f(val)
    }
    return a
}

func main() {
    alist := []int{4, 5, 6, 7}
    result := mapper(square, alist)
    fmt.Println(result)

}

Python Matplotlib figure title overlaps axes label when using twiny

I was having an issue with the x-label overlapping a subplot title; this worked for me:

import matplotlib.pyplot as plt
fig, ax = plt.subplots(2, 1)
ax[0].scatter(...)
ax[1].scatter(...)
plt.tight_layout()
.
.
.
plt.show()

before

enter image description here

after

enter image description here

reference:

.trim() in JavaScript not working in IE

Unfortunately there is not cross browser JavaScript support for trim().

If you aren't using jQuery (which has a .trim() method) you can use the following methods to add trim support to strings:

String.prototype.trim = function() {
    return this.replace(/^\s+|\s+$/g,"");
}
String.prototype.ltrim = function() {
    return this.replace(/^\s+/,"");
}
String.prototype.rtrim = function() {
    return this.replace(/\s+$/,"");
}

Changing ViewPager to enable infinite page scrolling

Its hacked by CustomPagerAdapter:

MainActivity.java:

import android.content.Context;
import android.os.Handler;
import android.os.Parcelable;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private List<String> numberList = new ArrayList<String>();
    private CustomPagerAdapter mCustomPagerAdapter;
    private ViewPager mViewPager;
    private Handler handler;
    private Runnable runnable;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        numberList.clear();
        for (int i = 0; i < 10; i++) {
        numberList.add(""+i);
        }

        mViewPager = (ViewPager)findViewById(R.id.pager);
        mCustomPagerAdapter = new CustomPagerAdapter(MainActivity.this);
        EndlessPagerAdapter mAdapater = new EndlessPagerAdapter(mCustomPagerAdapter);
        mViewPager.setAdapter(mAdapater);


        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                int modulo = position%numberList.size();
                Log.i("Current ViewPager View's Position", ""+modulo);

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

        handler = new Handler();
        runnable = new Runnable() {
            @Override
            public void run() {

                mViewPager.setCurrentItem(mViewPager.getCurrentItem()+1);
                handler.postDelayed(runnable, 1000);
            }
        };

        handler.post(runnable);

    }

    @Override
    protected void onDestroy() {
        if(handler!=null){
            handler.removeCallbacks(runnable);
        }
        super.onDestroy();
    }

    private class CustomPagerAdapter extends PagerAdapter {

        Context mContext;
        LayoutInflater mLayoutInflater;

        public CustomPagerAdapter(Context context) {
            mContext = context;
            mLayoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

        @Override
        public int getCount() {
            return numberList.size();
        }

        @Override
        public boolean isViewFromObject(View view, Object object) {
            return view == ((LinearLayout) object);
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            View itemView = mLayoutInflater.inflate(R.layout.row_item_viewpager, container, false);

            TextView textView = (TextView) itemView.findViewById(R.id.txtItem);
            textView.setText(numberList.get(position));
            container.addView(itemView);
            return itemView;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView((LinearLayout) object);
        }
    }

    private class EndlessPagerAdapter extends PagerAdapter {

        private static final String TAG = "EndlessPagerAdapter";
        private static final boolean DEBUG = false;

        private final PagerAdapter mPagerAdapter;

        EndlessPagerAdapter(PagerAdapter pagerAdapter) {
            if (pagerAdapter == null) {
                throw new IllegalArgumentException("Did you forget initialize PagerAdapter?");
            }
            if ((pagerAdapter instanceof FragmentPagerAdapter || pagerAdapter instanceof FragmentStatePagerAdapter) && pagerAdapter.getCount() < 3) {
                throw new IllegalArgumentException("When you use FragmentPagerAdapter or FragmentStatePagerAdapter, it only supports >= 3 pages.");
            }
            mPagerAdapter = pagerAdapter;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            if (DEBUG) Log.d(TAG, "Destroy: " + getVirtualPosition(position));
            mPagerAdapter.destroyItem(container, getVirtualPosition(position), object);

            if (mPagerAdapter.getCount() < 4) {
                mPagerAdapter.instantiateItem(container, getVirtualPosition(position));
            }
        }

        @Override
        public void finishUpdate(ViewGroup container) {
            mPagerAdapter.finishUpdate(container);
        }

        @Override
        public int getCount() {
            return Integer.MAX_VALUE; // this is the magic that we can scroll infinitely.
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mPagerAdapter.getPageTitle(getVirtualPosition(position));
        }

        @Override
        public float getPageWidth(int position) {
            return mPagerAdapter.getPageWidth(getVirtualPosition(position));
        }

        @Override
        public boolean isViewFromObject(View view, Object o) {
            return mPagerAdapter.isViewFromObject(view, o);
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            if (DEBUG) Log.d(TAG, "Instantiate: " + getVirtualPosition(position));
            return mPagerAdapter.instantiateItem(container, getVirtualPosition(position));
        }

        @Override
        public Parcelable saveState() {
            return mPagerAdapter.saveState();
        }

        @Override
        public void restoreState(Parcelable state, ClassLoader loader) {
            mPagerAdapter.restoreState(state, loader);
        }

        @Override
        public void startUpdate(ViewGroup container) {
            mPagerAdapter.startUpdate(container);
        }

        int getVirtualPosition(int realPosition) {
            return realPosition % mPagerAdapter.getCount();
        }

        PagerAdapter getPagerAdapter() {
            return mPagerAdapter;
        }

    }
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="180dp">
    </android.support.v4.view.ViewPager>

</RelativeLayout>

row_item_viewpager.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:gravity="center">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/txtItem"
        android:textAppearance="@android:style/TextAppearance.Large"/>

</LinearLayout>

Done

Android Activity as a dialog

1 - You can use the same activity as both dialog and full screen, dynamically:

Call setTheme(android.R.style.Theme_Dialog) before calling setContentView(...) and super.oncreate() in your Activity.

2 - If you don't plan to change the activity theme style you can use

<activity android:theme="@android:style/Theme.Dialog" />

(as mentioned by @faisal khan)

Float a div in top right corner without overlapping sibling header

section {
    position: relative;
    width: 50%;
    border: 1px solid;
}
h1 {
    display: inline;
}
div {
    position: relative;
    float:right;
    top: 0;
    right: 0;

}

Postgres ERROR: could not open file for reading: Permission denied

Copy your CSV file into the /tmp folder

Files named in a COPY command are read or written directly by the server, not by the client application. Therefore, they must reside on or be accessible to the database server machine, not the client. They must be accessible to and readable or writable by the PostgreSQL user (the user ID the server runs as), not the client. COPY naming a file is only allowed to database superusers, since it allows reading or writing any file that the server has privileges to access.

How can I open Java .class files in a human-readable way?

As suggested you can use JAD to decompile it and view the files. To make it easier to read you can use the JADclipse plugin for eclipse to integrate JAD directly to eclipse or use DJ Java Decompiler which is much easier to use than command line JAD

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 23: ordinal not in range(128)

I was getting this error when executing in python3,I got the same program working by simply executing in python2

What is the difference between concurrency and parallelism?

I really liked this graphical representation from another answer - I think it answers the question much better than a lot of the above answers

Parallelism vs Concurrency When two threads are running in parallel, they are both running at the same time. For example, if we have two threads, A and B, then their parallel execution would look like this:

CPU 1: A ------------------------->

CPU 2: B ------------------------->

When two threads are running concurrently, their execution overlaps. Overlapping can happen in one of two ways: either the threads are executing at the same time (i.e. in parallel, as above), or their executions are being interleaved on the processor, like so:

CPU 1: A -----------> B ----------> A -----------> B ---------->

So, for our purposes, parallelism can be thought of as a special case of concurrency

Source: Another answer here

Hope that helps.

Convert string to datetime

I have had success with:

require 'time'
t = Time.parse(some_string)

How to unbind a listener that is calling event.preventDefault() (using jQuery)?

Disable:

document.ontouchstart = function(e){ e.preventDefault(); }

Enable:

document.ontouchstart = function(e){ return true; }

How to print the array?

There is no .length property in C. The .length property can only be applied to arrays in object oriented programming (OOP) languages. The .length property is inherited from the object class; the class all other classes & objects inherit from in an OOP language. Also, one would use .length-1 to return the number of the last index in an array; using just the .length will return the total length of the array.

I would suggest something like this:

int index;
int jdex;
for( index = 0; index < (sizeof( my_array ) / sizeof( my_array[0] )); index++){
   for( jdex = 0; jdex < (sizeof( my_array ) / sizeof( my_array[0] )); jdex++){
        printf( "%d", my_array[index][jdex] );
        printf( "\n" );
   }
}

The line (sizeof( my_array ) / sizeof( my_array[0] )) will give you the size of the array in question. The sizeof property will return the length in bytes, so one must divide the total size of the array in bytes by how many bytes make up each element, each element takes up 4 bytes because each element is of type int, respectively. The array is of total size 16 bytes and each element is of 4 bytes so 16/4 yields 4 the total number of elements in your array because indexing starts at 0 and not 1.

Setting a WebRequest's body data

The answers in this topic are all great. However i'd like to propose another one. Most likely you have been given an api and want that into your c# project. Using Postman, you can setup and test the api call there and once it runs properly, you can simply click 'Code' and the request that you have been working on, is written to a c# snippet. like this:

var client = new RestClient("https://api.XXXXX.nl/oauth/token");
client.Timeout = -1;
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Basic   N2I1YTM4************************************jI0YzJhNDg=");
request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
request.AddParameter("grant_type", "password");
request.AddParameter("username", "[email protected]");
request.AddParameter("password", "XXXXXXXXXXXXX");
IRestResponse response = client.Execute(request);
Console.WriteLine(response.Content);

The code above depends on the nuget package RestSharp, which you can easily install.

How to change the href for a hyperlink using jQuery

This snippet invokes when a link of class 'menu_link' is clicked, and shows the text and url of the link. The return false prevents the link from being followed.

<a rel='1' class="menu_link" href="option1.html">Option 1</a>
<a rel='2' class="menu_link" href="option2.html">Option 2</a>

$('.menu_link').live('click', function() {
   var thelink = $(this);
   alert ( thelink.html() );
   alert ( thelink.attr('href') );
   alert ( thelink.attr('rel') );

   return false;
});

How do you style a TextInput in react native for password input

A little plus:

version = RN 0.57.7

secureTextEntry={true}

does not work when the keyboardType was "phone-pad" or "email-address"

html5: display video inside canvas

var canvas = document.getElementById('canvas');
var ctx    = canvas.getContext('2d');
var video  = document.getElementById('video');

video.addEventListener('play', function () {
    var $this = this; //cache
    (function loop() {
        if (!$this.paused && !$this.ended) {
            ctx.drawImage($this, 0, 0);
            setTimeout(loop, 1000 / 30); // drawing at 30fps
        }
    })();
}, 0);

I guess the above code is self Explanatory, If not drop a comment below, I will try to explain the above few lines of code

Edit :
here's an online example, just for you :)
Demo

_x000D_
_x000D_
var canvas = document.getElementById('canvas');_x000D_
var ctx = canvas.getContext('2d');_x000D_
var video = document.getElementById('video');_x000D_
_x000D_
// set canvas size = video size when known_x000D_
video.addEventListener('loadedmetadata', function() {_x000D_
  canvas.width = video.videoWidth;_x000D_
  canvas.height = video.videoHeight;_x000D_
});_x000D_
_x000D_
video.addEventListener('play', function() {_x000D_
  var $this = this; //cache_x000D_
  (function loop() {_x000D_
    if (!$this.paused && !$this.ended) {_x000D_
      ctx.drawImage($this, 0, 0);_x000D_
      setTimeout(loop, 1000 / 30); // drawing at 30fps_x000D_
    }_x000D_
  })();_x000D_
}, 0);
_x000D_
<div id="theater">_x000D_
  <video id="video" src="http://upload.wikimedia.org/wikipedia/commons/7/79/Big_Buck_Bunny_small.ogv" controls="false"></video>_x000D_
  <canvas id="canvas"></canvas>_x000D_
  <label>_x000D_
    <br />Try to play me :)</label>_x000D_
  <br />_x000D_
</div>
_x000D_
_x000D_
_x000D_

How do you find the sum of all the numbers in an array in Java?

In Java 8

Code:

   int[] array = new int[]{1,2,3,4,5};
   int sum = IntStream.of(array).reduce( 0,(a, b) -> a + b);
   System.out.println("The summation of array is " + sum);

  System.out.println("Another way to find summation :" + IntStream.of(array).sum());

Output:

The summation of array is 15
Another way to find summation :15

Explanation:

In Java 8, you can use reduction concept to do your addition.

Read all about Reduction

keyword not supported data source

I was getting the same problem.
but this code works good try it.

<add name="MyCon" connectionString="Server=****;initial catalog=PortalDb;user id=**;password=**;MultipleActiveResultSets=True;" providerName="System.Data.SqlClient" />

How to create a label inside an <input> element?

You do not need a Javascript code for that...
I think you mean the placeholder attribute. Here is the code:

<input type="text" placeholder="Your descriptive text goes here...">



The default text will be grey-ish and when clicked, it will dissapear!

Replacing a fragment with another fragment inside activity group

In kotlin you can do:

// instantiate the new fragment
val fragment: Fragment = ExampleFragment()

val transaction = supportFragmentManager.beginTransaction()
transaction.replace(R.id.book_description_fragment, fragment)
transaction.addToBackStack("transaction_name")
// Commit the transaction
transaction.commit()

Permission to write to the SD card

The suggested technique above in Dave's answer is certainly a good design practice, and yes ultimately the required permission must be set in the AndroidManifest.xml file to access the external storage.

However, the Mono-esque way to add most (if not all, not sure) "manifest options" is through the attributes of the class implementing the activity (or service).

The Visual Studio Mono plugin automatically generates the manifest, so its best not to manually tamper with it (I'm sure there are cases where there is no other option).

For example:

[Activity(Label="MonoDroid App", MainLauncher=true, Permission="android.permission.WRITE_EXTERNAL_STORAGE")]
public class MonoActivity : Activity
{
  protected override void OnCreate(Bundle bindle)
  {
    base.OnCreate(bindle);
  }
}

Merge data frames based on rownames in R

See ?merge:

the name "row.names" or the number 0 specifies the row names.

Example:

R> de <- merge(d, e, by=0, all=TRUE)  # merge by row names (by=0 or by="row.names")
R> de[is.na(de)] <- 0                 # replace NA values
R> de
  Row.names   a   b   c   d   e   f   g   h   i  j  k  l  m  n  o  p  q  r  s
1         1 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 11 12 13 14 15 16 17 18 19
2         2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  1  0  0  0  0  0  0  0  0  0
3         3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  0 21 22 23 24 25 26 27 28 29
   t
1 20
2  0
3 30

How to configure log4j with a properties file

I believe the log4j.properties directory it needs to be in the java classpath. In your case adding the CWD to the classpath should work.

Large WCF web service request failing with (400) HTTP Bad Request

I was also getting this issue also however none of the above worked for me as I was using a custom binding (for BinaryXML) after an long time digging I found the answer here :-

Sending large XML from Silverlight to WCF

As am using a customBinding, the maxReceivedMessageSize has to be set on the httpTransport element under the binding element in the web.config:

<httpsTransport maxReceivedMessageSize="4194304" /> 

What is the purpose of the "final" keyword in C++11 for functions?

Supplement to Mario Knezovic 's answer:

class IA
{
public:
  virtual int getNum() const = 0;
};

class BaseA : public IA
{
public:
 inline virtual int getNum() const final {return ...};
};

class ImplA : public BaseA {...};

IA* pa = ...;
...
ImplA* impla = static_cast<ImplA*>(pa);

//the following line should cause compiler to use the inlined function BaseA::getNum(), 
//instead of dynamic binding (via vtable or something).
//any class/subclass of BaseA will benefit from it

int n = impla->getNum();

The above code shows the theory, but not actually tested on real compilers. Much appreciated if anyone paste a disassembled output.

How do I measure separate CPU core usage for a process?

You can use:

 mpstat -P ALL 1

It shows how much each core is busy and it updates automatically each second. The output would be something like this (on a quad-core processor):

10:54:41 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest   %idle
10:54:42 PM  all    8.20    0.12    0.75    0.00    0.00    0.00    0.00    0.00   90.93
10:54:42 PM    0   24.00    0.00    2.00    0.00    0.00    0.00    0.00    0.00   74.00
10:54:42 PM    1   22.00    0.00    2.00    0.00    0.00    0.00    0.00    0.00   76.00
10:54:42 PM    2    2.02    1.01    0.00    0.00    0.00    0.00    0.00    0.00   96.97
10:54:42 PM    3    2.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00   98.00
10:54:42 PM    4   14.15    0.00    1.89    0.00    0.00    0.00    0.00    0.00   83.96
10:54:42 PM    5    1.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00   99.00
10:54:42 PM    6    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
10:54:42 PM    7    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00

This command doesn't answer original question though i.e. it does not show CPU core usage for a specific process.

Rails find_or_create_by more than one attribute?

By passing a block to find_or_create, you can pass additional parameters that will be added to the object if it is created new. This is useful if you are validating the presence of a field that you aren't searching by.

Assuming:

class GroupMember < ActiveRecord::Base
    validates_presence_of :name
end

then

GroupMember.where(:member_id => 4, :group_id => 7).first_or_create { |gm| gm.name = "John Doe" }

will create a new GroupMember with the name "John Doe" if it doesn't find one with member_id 4 and group_id 7

Sql server - log is full due to ACTIVE_TRANSACTION

Restarting the SQL Server will clear up the log space used by your database. If this however is not an option, you can try the following:

* Issue a CHECKPOINT command to free up log space in the log file.

* Check the available log space with DBCC SQLPERF('logspace'). If only a small 
  percentage of your log file is actually been used, you can try a DBCC SHRINKFILE 
  command. This can however possibly introduce corruption in your database. 

* If you have another drive with space available you can try to add a file there in 
  order to get enough space to attempt to resolve the issue.

Hope this will help you in finding your solution.

Reference to a non-shared member requires an object reference occurs when calling public sub

You either have to make the method Shared or use an instance of the class General:

Dim gen = New General()
gen.updateDynamics(get_prospect.dynamicsID)

or

General.updateDynamics(get_prospect.dynamicsID)

Public Shared Sub updateDynamics(dynID As Int32)
    ' ... '
End Sub

Shared(VB.NET)

How to convert integer to char in C?

A char in C is already a number (the character's ASCII code), no conversion required.

If you want to convert a digit to the corresponding character, you can simply add '0':

c = i +'0';

The '0' is a character in the ASCll table.

What is Node.js' Connect, Express and "middleware"?

node.js

Node.js is a javascript motor for the server side.
In addition to all the js capabilities, it includes networking capabilities (like HTTP), and access to the file system.
This is different from client-side js where the networking tasks are monopolized by the browser, and access to the file system is forbidden for security reasons.

node.js as a web server: express

Something that runs in the server, understands HTTP and can access files sounds like a web server. But it isn't one.
To make node.js behave like a web server one has to program it: handle the incoming HTTP requests and provide the appropriate responses.
This is what Express does: it's the implementation of a web server in js.
Thus, implementing a web site is like configuring Express routes, and programming the site's specific features.

Middleware and Connect

Serving pages involves a number of tasks. Many of those tasks are well known and very common, so node's Connect module (one of the many modules available to run under node) implements those tasks.
See the current impressing offering:

  • logger request logger with custom format support
  • csrf Cross-site request forgery protection
  • compress Gzip compression middleware
  • basicAuth basic http authentication
  • bodyParser extensible request body parser
  • json application/json parser
  • urlencoded application/x-www-form-urlencoded parser
  • multipart multipart/form-data parser
  • timeout request timeouts
  • cookieParser cookie parser
  • session session management support with bundled MemoryStore
  • cookieSession cookie-based session support
  • methodOverride faux HTTP method support
  • responseTime calculates response-time and exposes via X-Response-Time
  • staticCache memory cache layer for the static() middleware
  • static streaming static file server supporting Range and more
  • directory directory listing middleware
  • vhost virtual host sub-domain mapping middleware
  • favicon efficient favicon server (with default icon)
  • limit limit the bytesize of request bodies
  • query automatic querystring parser, populating req.query
  • errorHandler flexible error handler

Connect is the framework and through it you can pick the (sub)modules you need.
The Contrib Middleware page enumerates a long list of additional middlewares.
Express itself comes with the most common Connect middlewares.

What to do?

Install node.js.
Node comes with npm, the node package manager.
The command npm install -g express will download and install express globally (check the express guide).
Running express foo in a command line (not in node) will create a ready-to-run application named foo. Change to its (newly created) directory and run it with node with the command node <appname>, then open http://localhost:3000 and see. Now you are in.

Insert php variable in a href

echo '<a href="' . $folder_path . '">Link text</a>';

Please note that you must use the path relative to your domain and, if the folder path is outside the public htdocs directory, it will not work.

EDIT: maybe i misreaded the question; you have a file on your pc and want to insert the path on the html page, and then send it to the server?

rotate image with css

The trouble looks like the image isn't square and the browser adjusts as such. After rotation ensure the dimensions are retained by changing the image margin.

.imagetest img {
  transform: rotate(270deg);
  ...
  margin: 10px 0px;
}

The amount will depend on the difference in height x width of the image. You may also need to add display:inline-block; or display:block to get it to recognize the margin parameter.

How do I choose the URL for my Spring Boot webapp?

The server.contextPath or server.context-path works if

in pom.xml

  1. packing should be war not jar
  2. Add following dependencies

    <dependency>
        <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <!-- Tomcat/TC server -->
     <dependency>
         <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
        <scope>provided</scope>
     </dependency>
    

    In eclipse, right click on project --> Run as --> Spring Boot App.

How do I get the SharedPreferences from a PreferenceActivity in Android?

Declare these methods first..

public static void putPref(String key, String value, Context context) {
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
    SharedPreferences.Editor editor = prefs.edit();
    editor.putString(key, value);
    editor.commit();
}

public static String getPref(String key, Context context) {
    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
    return preferences.getString(key, null);
}

Then call this when you want to put a pref:

putPref("myKey", "mystring", getApplicationContext());

call this when you want to get a pref:

getPref("myKey", getApplicationContext());

Or you can use this object https://github.com/kcochibili/TinyDB--Android-Shared-Preferences-Turbo which simplifies everything even further

Example:

TinyDB tinydb = new TinyDB(context);

tinydb.putInt("clickCount", 2);
tinydb.putFloat("xPoint", 3.6f);
tinydb.putLong("userCount", 39832L);

tinydb.putString("userName", "john");
tinydb.putBoolean("isUserMale", true); 

tinydb.putList("MyUsers", mUsersArray);
tinydb.putImagePNG("DropBox/WorkImages", "MeAtlunch.png", lunchBitmap);

How to run a bash script from C++ program

Use the system function.

system("myfile.sh"); // myfile.sh should be chmod +x

Get a substring of a char*

char subbuff[5];
memcpy( subbuff, &buff[10], 4 );
subbuff[4] = '\0';

Job done :)

Java JSON serialization - best practice

Are you tied to this library? Google Gson is very popular. I have myself not used it with Generics but their front page says Gson considers support for Generics very important.

How to remove padding around buttons in Android?

For me the problem turned out to be minHeight and minWidth on some of the Android themes.

On the Button element, add:

<Button android:minHeight="0dp" android:minWidth="0dp" ...

Or in your button's style:

<item name="android:minHeight">0dp</item>
<item name="android:minWidth">0dp</item>

How to find the index of an element in an array in Java?

In this case, you could create e new String from your array of chars and then do an indeoxOf("e") on that String:

System.out.println(new String(list).indexOf("e")); 

But in other cases of primitive data types, you'll have to iterate over it.

How to access random item in list?

Create a Random instance:

Random rnd = new Random();

Fetch a random string:

string s = arraylist[rnd.Next(arraylist.Count)];

Remember though, that if you do this frequently you should re-use the Random object. Put it as a static field in the class so it's initialized only once and then access it.

What is the pythonic way to detect the last element in a 'for' loop?

if the items are unique:

for x in list:
    #code
    if x == list[-1]:
        #code

other options:

pos = -1
for x in list:
    pos += 1
    #code
    if pos == len(list) - 1:
        #code


for x in list:
    #code
#code - e.g. print x


if len(list) > 0:
    for x in list[:-1]
        #code
    for x in list[-1]:
        #code

Convert line endings

Doing this with POSIX is tricky:

  • POSIX Sed does not support \r or \15. Even if it did, the in place option -i is not POSIX

  • POSIX Awk does support \r and \15, however the -i inplace option is not POSIX

  • d2u and dos2unix are not POSIX utilities, but ex is

  • POSIX ex does not support \r, \15, \n or \12

To remove carriage returns:

awk 'BEGIN{RS="^$";ORS="";getline;gsub("\r","");print>ARGV[1]}' file

To add carriage returns:

awk 'BEGIN{RS="^$";ORS="";getline;gsub("\n","\r&");print>ARGV[1]}' file

Website screenshots

I'm on Windows so I was able to use the imagegrabwindow function after reading the tip on here from stephan. I added in cropping (to get rid of the Browser header, scroll bars, etc.) and resizing to get a final image. Here's my code. Hope that helps someone.

Convert string to hex-string in C#

According to this snippet here, this approach should be good for long strings:

private string StringToHex(string hexstring)
{
    StringBuilder sb = new StringBuilder();
    foreach (char t in hexstring)
    { 
        //Note: X for upper, x for lower case letters
        sb.Append(Convert.ToInt32(t).ToString("x")); 
    }
    return sb.ToString();
}

usage:

string result = StringToHex("Hello world"); //returns "48656c6c6f20776f726c64"

Another approach in one line

string input = "Hello world";
string result = String.Concat(input.Select(x => ((int)x).ToString("x")));

Array of Matrices in MATLAB

myArrayOfMatrices = zeros(unknown,500,800);

If you're running out of memory throw more RAM in your system, and make sure you're running a 64 bit OS. Also try reducing your precision (do you really need doubles or can you get by with singles?):

myArrayOfMatrices = zeros(unknown,500,800,'single');

To append to that array try:

myArrayOfMatrices(unknown+1,:,:) = zeros(500,800);

Read Post Data submitted to ASP.Net Form

NameValueCollection nvclc = Request.Form;
string   uName= nvclc ["txtUserName"];
string   pswod= nvclc ["txtPassword"];
//try login
CheckLogin(uName, pswod);

Flask Value error view function did not return a response

The following does not return a response:

You must return anything like return afunction() or return 'a string'.

This can solve the issue

Retrofit and GET using parameters

I also wanted to clarify that if you have complex url parameters to build, you will need to build them manually. ie if your query is example.com/?latlng=-37,147, instead of providing the lat and lng values individually, you will need to build the latlng string externally, then provide it as a parameter, ie:

public interface LocationService {    
    @GET("/example/")
    void getLocation(@Query(value="latlng", encoded=true) String latlng);
}

Note the encoded=true is necessary, otherwise retrofit will encode the comma in the string parameter. Usage:

String latlng = location.getLatitude() + "," + location.getLongitude();
service.getLocation(latlng);

What is a tracking branch?

This was how I added a tracking branch so I can pull from it into my new branch:

git branch --set-upstream-to origin/Development new-branch

Change mysql user password using command line

Note: u should login as root user

 SET PASSWORD FOR 'root'@'localhost' = PASSWORD('your password');

PowerShell: Run command from script's directory

I made a one-liner out of @JohnL's solution:

$MyInvocation.MyCommand.Path | Split-Path | Push-Location

How to get last inserted row ID from WordPress database?

just like this :

global $wpdb;
$table_name='lorem_ipsum';
$results = $wpdb->get_results("SELECT * FROM $table_name ORDER BY ID DESC LIMIT 1");
print_r($results[0]->id);

simply your selecting all the rows then order them DESC by id , and displaying only the first

Cannot start session without errors in phpMyAdmin

In my case, problem was due to low disk space. I want to mention it for other users like me :)

How to check if an object is a certain type

Some more details in relation with the response from Cody Gray. As it took me some time to digest it I though it might be usefull to others.

First, some definitions:

  1. There are TypeNames, which are string representations of the type of an object, interface, etc. For example, Bar is a TypeName in Public Class Bar, or in Dim Foo as Bar. TypeNames could be seen as "labels" used in the code to tell the compiler which type definition to look for in a dictionary where all available types would be described.
  2. There are System.Type objects which contain a value. This value indicates a type; just like a String would take some text or an Int would take a number, except we are storing types instead of text or numbers. Type objects contain the type definitions, as well as its corresponding TypeName.

Second, the theory:

  1. Foo.GetType() returns a Type object which contains the type for the variable Foo. In other words, it tells you what Foo is an instance of.
  2. GetType(Bar) returns a Type object which contains the type for the TypeName Bar.
  3. In some instances, the type an object has been Cast to is different from the type an object was first instantiated from. In the following example, MyObj is an Integer cast into an Object:

    Dim MyVal As Integer = 42 Dim MyObj As Object = CType(MyVal, Object)

So, is MyObj of type Object or of type Integer? MyObj.GetType() will tell you it is an Integer.

  1. But here comes the Type Of Foo Is Bar feature, which allows you to ascertain a variable Foo is compatible with a TypeName Bar. Type Of MyObj Is Integer and Type Of MyObj Is Object will both return True. For most cases, TypeOf will indicate a variable is compatible with a TypeName if the variable is of that Type or a Type that derives from it. More info here: https://docs.microsoft.com/en-us/dotnet/visual-basic/language-reference/operators/typeof-operator#remarks

The test below illustrate quite well the behaviour and usage of each of the mentionned keywords and properties.

Public Sub TestMethod1()

    Dim MyValInt As Integer = 42
    Dim MyValDble As Double = CType(MyValInt, Double)
    Dim MyObj As Object = CType(MyValDble, Object)

    Debug.Print(MyValInt.GetType.ToString) 'Returns System.Int32
    Debug.Print(MyValDble.GetType.ToString) 'Returns System.Double
    Debug.Print(MyObj.GetType.ToString) 'Returns System.Double

    Debug.Print(MyValInt.GetType.GetType.ToString) 'Returns System.RuntimeType
    Debug.Print(MyValDble.GetType.GetType.ToString) 'Returns System.RuntimeType
    Debug.Print(MyObj.GetType.GetType.ToString) 'Returns System.RuntimeType

    Debug.Print(GetType(Integer).GetType.ToString) 'Returns System.RuntimeType
    Debug.Print(GetType(Double).GetType.ToString) 'Returns System.RuntimeType
    Debug.Print(GetType(Object).GetType.ToString) 'Returns System.RuntimeType

    Debug.Print(MyValInt.GetType = GetType(Integer)) '# Returns True
    Debug.Print(MyValInt.GetType = GetType(Double)) 'Returns False
    Debug.Print(MyValInt.GetType = GetType(Object)) 'Returns False

    Debug.Print(MyValDble.GetType = GetType(Integer)) 'Returns False
    Debug.Print(MyValDble.GetType = GetType(Double)) '# Returns True
    Debug.Print(MyValDble.GetType = GetType(Object)) 'Returns False

    Debug.Print(MyObj.GetType = GetType(Integer)) 'Returns False
    Debug.Print(MyObj.GetType = GetType(Double)) '# Returns True
    Debug.Print(MyObj.GetType = GetType(Object)) 'Returns False

    Debug.Print(TypeOf MyObj Is Integer) 'Returns False
    Debug.Print(TypeOf MyObj Is Double) '# Returns True
    Debug.Print(TypeOf MyObj Is Object) '# Returns True


End Sub

EDIT

You can also use Information.TypeName(Object) to get the TypeName of a given object. For example,

Dim Foo as Bar
Dim Result as String
Result = TypeName(Foo)
Debug.Print(Result) 'Will display "Bar"

How to extract 1 screenshot for a video with ffmpeg at a given time?

FFMpeg can do this by seeking to the given timestamp and extracting exactly one frame as an image, see for instance:

ffmpeg -i input_file.mp4 -ss 01:23:45 -vframes 1 output.jpg

Let's explain the options:

-i input file           the path to the input file
-ss 01:23:45            seek the position to the specified timestamp
-vframes 1              only handle one video frame
output.jpg              output filename, should have a well-known extension

The -ss parameter accepts a value in the form HH:MM:SS[.xxx] or as a number in seconds. If you need a percentage, you need to compute the video duration beforehand.

Check if character is number?

You could use comparison operators to see if it is in the range of digit characters:

var c = justPrices[i].substr(commapos+2,1);
if (c >= '0' && c <= '9') {
    // it is a number
} else {
    // it isn't
}

DataAdapter.Fill(Dataset)

DataSet ds = new DataSet();

using (OleDbConnection connection = new OleDbConnection(connectionString))
using (OleDbCommand command = new OleDbCommand(query, connection))
using (OleDbDataAdapter adapter = new OleDbDataAdapter(command))
{
    adapter.Fill(ds);
}

return ds;

Differences between action and actionListener

ActionListener gets fired first, with an option to modify the response, before Action gets called and determines the location of the next page.

If you have multiple buttons on the same page which should go to the same place but do slightly different things, you can use the same Action for each button, but use a different ActionListener to handle slightly different functionality.

Here is a link that describes the relationship:

http://www.java-samples.com/showtutorial.php?tutorialid=605

Iterator invalidation rules

C++03 (Source: Iterator Invalidation Rules (C++03))


Insertion

Sequence containers

  • vector: all iterators and references before the point of insertion are unaffected, unless the new container size is greater than the previous capacity (in which case all iterators and references are invalidated) [23.2.4.3/1]
  • deque: all iterators and references are invalidated, unless the inserted member is at an end (front or back) of the deque (in which case all iterators are invalidated, but references to elements are unaffected) [23.2.1.3/1]
  • list: all iterators and references unaffected [23.2.2.3/1]

Associative containers

  • [multi]{set,map}: all iterators and references unaffected [23.1.2/8]

Container adaptors

  • stack: inherited from underlying container
  • queue: inherited from underlying container
  • priority_queue: inherited from underlying container

Erasure

Sequence containers

  • vector: every iterator and reference after the point of erase is invalidated [23.2.4.3/3]
  • deque: all iterators and references are invalidated, unless the erased members are at an end (front or back) of the deque (in which case only iterators and references to the erased members are invalidated) [23.2.1.3/4]
  • list: only the iterators and references to the erased element is invalidated [23.2.2.3/3]

Associative containers

  • [multi]{set,map}: only iterators and references to the erased elements are invalidated [23.1.2/8]

Container adaptors

  • stack: inherited from underlying container
  • queue: inherited from underlying container
  • priority_queue: inherited from underlying container

Resizing

  • vector: as per insert/erase [23.2.4.2/6]
  • deque: as per insert/erase [23.2.1.2/1]
  • list: as per insert/erase [23.2.2.2/1]

Note 1

Unless otherwise specified (either explicitly or by defining a function in terms of other functions), invoking a container member function or passing a container as an argument to a library function shall not invalidate iterators to, or change the values of, objects within that container. [23.1/11]

Note 2

It's not clear in C++2003 whether "end" iterators are subject to the above rules; you should assume, anyway, that they are (as this is the case in practice).

Note 3

The rules for invalidation of pointers are the sames as the rules for invalidation of references.

C# Inserting Data from a form into an access Database

My Code to insert data is not working. It showing no error but data is not showing in my database.

public partial class Form1 : Form { OleDbConnection connection = new OleDbConnection(check.Properties.Settings.Default.KitchenConnectionString); public Form1() { InitializeComponent(); }

    private void Form1_Load(object sender, EventArgs e)
    {
        
    }

    private void btn_add_Click(object sender, EventArgs e)
    {
        OleDbDataAdapter items = new OleDbDataAdapter();
        connection.Open();
        OleDbCommand command = new OleDbCommand("insert into Sets(SetId, SetName,  SetPassword) values('"+txt_id.Text+ "','" + txt_setname.Text + "','" + txt_password.Text + "');", connection);
        command.CommandType = CommandType.Text;
        command.ExecuteReader();
        connection.Close();
        MessageBox.Show("Insertd!");
    }
}

How can I obtain the element-wise logical NOT of a pandas Series?

To invert a boolean Series, use ~s:

In [7]: s = pd.Series([True, True, False, True])

In [8]: ~s
Out[8]: 
0    False
1    False
2     True
3    False
dtype: bool

Using Python2.7, NumPy 1.8.0, Pandas 0.13.1:

In [119]: s = pd.Series([True, True, False, True]*10000)

In [10]:  %timeit np.invert(s)
10000 loops, best of 3: 91.8 µs per loop

In [11]: %timeit ~s
10000 loops, best of 3: 73.5 µs per loop

In [12]: %timeit (-s)
10000 loops, best of 3: 73.5 µs per loop

As of Pandas 0.13.0, Series are no longer subclasses of numpy.ndarray; they are now subclasses of pd.NDFrame. This might have something to do with why np.invert(s) is no longer as fast as ~s or -s.

Caveat: timeit results may vary depending on many factors including hardware, compiler, OS, Python, NumPy and Pandas versions.

printf, wprintf, %s, %S, %ls, char* and wchar*: Errors not announced by a compiler warning?

%S seems to conform to The Single Unix Specification v2 and is also part of the current (2008) POSIX specification.

Equivalent C99 conforming format specifiers would be %s and %ls.

Visual Studio 2017 - Could not load file or assembly 'System.Runtime, Version=4.1.0.0' or one of its dependencies

Before running the unit tests, just remove the runtime tags from app.config file. Problem will be solved.

Calling Javascript from a html form

You can either use javascript url form with

<form action="javascript:handleClick()">

Or use onSubmit event handler

<form onSubmit="return handleClick()">

In the later form, if you return false from the handleClick it will prevent the normal submision procedure. Return true if you want the browser to follow normal submision procedure.

Your onSubmit event handler in the button also fails because of the Javascript: part

EDIT: I just tried this code and it works:

<html>
  <head>
    <script type="text/javascript">

      function handleIt() {
        alert("hello");
      }

    </script>
  </head>

<body>
    <form name="myform" action="javascript:handleIt()">
      <input name="Submit"  type="submit" value="Update"/>
    </form>
</body>
</html>

jQuery scrollTop not working in Chrome but working in Firefox

I don't think the scrollTop is a valid property. If you want to animate scrolling, try the scrollTo plugin for jquery

http://plugins.jquery.com/project/ScrollTo

Why can't I display a pound (£) symbol in HTML?

You need to save your PHP script file in UTF-8 encoding, and leave the <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> in the HTML.

For text editor, I recommend Notepad++, because it can detect and display the actual encoding of the file (in the lower right corner of the editor), and you can convert it as well.

Print the stack trace of an exception

I have created a method that helps with getting the stackTrace:

private static String getStackTrace(Exception ex) {
    StringBuffer sb = new StringBuffer(500);
    StackTraceElement[] st = ex.getStackTrace();
    sb.append(ex.getClass().getName() + ": " + ex.getMessage() + "\n");
    for (int i = 0; i < st.length; i++) {
      sb.append("\t at " + st[i].toString() + "\n");
    }
    return sb.toString();
}

Java dynamic array sizes?

No you can't change the size of an array once created. You either have to allocate it bigger than you think you'll need or accept the overhead of having to reallocate it needs to grow in size. When it does you'll have to allocate a new one and copy the data from the old to the new:

int[] oldItems = new int[10];
for (int i = 0; i < 10; i++) {
    oldItems[i] = i + 10;
}
int[] newItems = new int[20];
System.arraycopy(oldItems, 0, newItems, 0, 10);
oldItems = newItems;

If you find yourself in this situation, I'd highly recommend using the Java Collections instead. In particular ArrayList essentially wraps an array and takes care of the logic for growing the array as required:

List<XClass> myclass = new ArrayList<XClass>();
myclass.add(new XClass());
myclass.add(new XClass());

Generally an ArrayList is a preferable solution to an array anyway for several reasons. For one thing, arrays are mutable. If you have a class that does this:

class Myclass {
    private int[] items;

    public int[] getItems() {
        return items;
    }
}

you've created a problem as a caller can change your private data member, which leads to all sorts of defensive copying. Compare this to the List version:

class Myclass {
    private List<Integer> items;

    public List<Integer> getItems() {
        return Collections.unmodifiableList(items);
    }
}

Unit testing private methods in C#

You can use PrivateObject Class

Class target = new Class();
PrivateObject obj = new PrivateObject(target);
var retVal = obj.Invoke("PrivateMethod");
Assert.AreEqual(expectedVal, retVal);

Note: PrivateObject and PrivateType are not available for projects targeting netcoreapp2.0 - GitHub Issue 366

Delete topic in Kafka 0.8.1.1

Andrea is correct. we can do it using command line.

And we still can program it, by

ZkClient zkClient = new ZkClient("localhost:2181", 10000);
zkClient.deleteRecursive(ZkUtils.getTopicPath("test2"));

Actually I do not recommend you delete topic on Kafka 0.8.1.1. I can delete this topic by this method, but if you check log for zookeeper, deletion mess it up.

MySQL: Set user variable from result of query

Just add parenthesis around the query:

set @user = 123456;
set @group = (select GROUP from USER where User = @user);
select * from USER where GROUP = @group;

Set selected item in Android BottomNavigationView

private void setSelectedItem(int actionId) {
    Menu menu = viewBottom.getMenu();
    for (int i = 0, size = menu.size(); i < size; i++) {
        MenuItem menuItem = menu.getItem(i);
        ((MenuItemImpl) menuItem).setExclusiveCheckable(false);
        menuItem.setChecked(menuItem.getItemId() == actionId);
        ((MenuItemImpl) menuItem).setExclusiveCheckable(true);
    }
}

The only 'minus' of the solution is using MenuItemImpl, which is 'internal' to library (though public).

Form Validation With Bootstrap (jQuery)

Please try after removing divs from formor try to use onclick method on submit button.

Postman Chrome: What is the difference between form-data, x-www-form-urlencoded and raw

Here are some supplemental examples to see the raw text that Postman passes in the request. You can see this by opening the Postman console:

enter image description here

form-data

Header

content-type: multipart/form-data; boundary=--------------------------590299136414163472038474

Body

key1=value1key2=value2

x-www-form-urlencoded

Header

Content-Type: application/x-www-form-urlencoded

Body

key1=value1&key2=value2

Raw text/plain

Header

Content-Type: text/plain

Body

This is some text.

Raw json

Header

Content-Type: application/json

Body

{"key1":"value1","key2":"value2"}

Stop embedded youtube iframe?

Here is a codepen, it worked for me.

I was searching for the simplest solution for embedding the YT video within an iframe, and I feel this is it.

What I needed was to have the video appear in a modal window and stop playing when it was closed

Here is the code : (from: https://codepen.io/anon/pen/GBjqQr)

    <div><a href="#" class="play-video">Play Video</a></div>
    <div><a href="#" class="stop-video">Stop Video</a></div>
    <div><a href="#" class="pause-video">Pause Video</a></div>

    <iframe class="youtube-video" width="560" height="315" src="https://www.youtube.com/embed/glEiPXAYE-U?enablejsapi=1&version=3&playerapiid=ytplayer" frameborder="0" allowfullscreen></iframe>

$('a.play-video').click(function(){
    $('.youtube-video')[0].contentWindow.postMessage('{"event":"command","func":"' + 'playVideo' + '","args":""}', '*');
});

$('a.stop-video').click(function(){
    $('.youtube-video')[0].contentWindow.postMessage('{"event":"command","func":"' + 'stopVideo' + '","args":""}', '*');
});

$('a.pause-video').click(function(){
    $('.youtube-video')[0].contentWindow.postMessage('{"event":"command","func":"' + 'pauseVideo' + '","args":""}', '*');
});

Additionally, if you want it to autoplay in a DOM-object that is not yet visible, such as a modal window, if I used the same button to play the video that I was using to show the modal it would not work so I used THIS:

https://www.youtube.com/embed/EzAGZCPSOfg?autoplay=1&enablejsapi=1&version=3&playerapiid=ytplayer

Note: The ?autoplay=1& where it's placed and the use of the '&' before the next property to allow the pause to continue to work.

How to call a javaScript Function in jsp on page load without using <body onload="disableView()">

Either use window.onload this way

<script>
    window.onload = function() {
        // ...
    }
</script>

or alternatively

<script>
    window.onload = functionName;
</script>

(yes, without the parentheses)


Or just put the script at the very bottom of page, right before </body>. At that point, all HTML DOM elements are ready to be accessed by document functions.

<body>
    ...

    <script>
        functionName();
    </script>
</body>

Python 2.7.10 error "from urllib.request import urlopen" no module named request

You can program defensively, and do your import as:

try:
    from urllib.request import urlopen
except ImportError:
    from urllib2 import urlopen

and then in the code, just use:

data = urlopen(MIRRORS).read(AMOUNT2READ)

Cannot read property 'map' of undefined

First of all, set more safe initial data:

getInitialState : function() {
    return {data: {comments:[]}};
},

And ensure your ajax data.

It should work if you follow above two instructions like Demo.

Updated: you can just wrap the .map block with conditional statement.

if (this.props.data) {
  var commentNodes = this.props.data.map(function (comment){
      return (
        <div>
          <h1>{comment.author}</h1>
        </div>
      );
  });
}

Content Security Policy: The page's settings blocked the loading of a resource

You can disable them in your browser.

Firefox

Type about:config in the Firefox address bar and find security.csp.enable and set it to false.

Chrome

You can install the extension called Disable Content-Security-Policy to disable CSP.

How to show current time in JavaScript in the format HH:MM:SS?

new Date().toLocaleTimeString('it-IT')

The it-IT locale happens to pad the hour if needed and omits PM or AM 01:33:01

svn over HTTP proxy

If you're using the standard SVN installation the svn:// connection will work on tcpip port 3690 and so it's basically impossible to connect unless you change your network configuration (you said only Http traffic is allowed) or you install the http module and Apache on the server hosting your SVN server.

How to extract duration time from ffmpeg output?

If you want to retrieve the length (and possibly all other metadata) from your media file with ffmpeg by using a python script you could try this:

import subprocess
import json

input_file  = "< path to your input file here >"

metadata = subprocess.check_output(f"ffprobe -i {input_file} -v quiet -print_format json -show_format -hide_banner".split(" "))

metadata = json.loads(metadata)
print(f"Length of file is: {float(metadata['format']['duration'])}")
print(metadata)

Output:

Length of file is: 7579.977143

{
  "streams": [
    {
      "index": 0,
      "codec_name": "mp3",
      "codec_long_name": "MP3 (MPEG audio layer 3)",
      "codec_type": "audio",
      "codec_time_base": "1/44100",
      "codec_tag_string": "[0][0][0][0]",
      "codec_tag": "0x0000",
      "sample_fmt": "fltp",
      "sample_rate": "44100",
      "channels": 2,
      "channel_layout": "stereo",
      "bits_per_sample": 0,
      "r_frame_rate": "0/0",
      "avg_frame_rate": "0/0",
      "time_base": "1/14112000",
      "start_pts": 353600,
      "start_time": "0.025057",
      "duration_ts": 106968637440,
      "duration": "7579.977143",
      "bit_rate": "320000",
      ...
      ...

Close Window from ViewModel

My proffered way is Declare event in ViewModel and use blend InvokeMethodAction as below.

Sample ViewModel

public class MainWindowViewModel : BindableBase, ICloseable
{
    public DelegateCommand SomeCommand { get; private set; }
    #region ICloseable Implementation
    public event EventHandler CloseRequested;        

    public void RaiseCloseNotification()
    {
        var handler = CloseRequested;
        if (handler != null)
        {
            handler.Invoke(this, EventArgs.Empty);
        }
    }
    #endregion

    public MainWindowViewModel()
    {
        SomeCommand = new DelegateCommand(() =>
        {
            //when you decide to close window
            RaiseCloseNotification();
        });
    }
}

I Closeable interface is as below but don't require to perform this action. ICloseable will help in creating generic view service, so if you construct view and ViewModel by dependency injection then what you can do is

internal interface ICloseable
{
    event EventHandler CloseRequested;
}

Use of ICloseable

var viewModel = new MainWindowViewModel();
        // As service is generic and don't know whether it can request close event
        var window = new Window() { Content = new MainView() };
        var closeable = viewModel as ICloseable;
        if (closeable != null)
        {
            closeable.CloseRequested += (s, e) => window.Close();
        }

And Below is Xaml, You can use this xaml even if you don't implement interface, it will only need your view model to raise CloseRquested.

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WPFRx"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions" 
xmlns:ViewModels="clr-namespace:WPFRx.ViewModels" x:Name="window" x:Class="WPFRx.MainWindow"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525" 
d:DataContext="{d:DesignInstance {x:Type ViewModels:MainWindowViewModel}}">

<i:Interaction.Triggers>
    <i:EventTrigger SourceObject="{Binding Mode=OneWay}" EventName="CloseRequested" >
        <ei:CallMethodAction TargetObject="{Binding ElementName=window}" MethodName="Close"/>
    </i:EventTrigger>
</i:Interaction.Triggers>

<Grid>
    <Button Content="Some Content" Command="{Binding SomeCommand}" Width="100" Height="25"/>
</Grid>

Cannot find pkg-config error

For Ubuntu/Debian OS,

apt-get install -y pkg-config

For Redhat/Yum OS,

yum install -y pkgconfig

For Archlinux OS,

pacman -S pkgconf

How do I pass JavaScript values to Scriptlet in JSP?

Its not possible as you are expecting. But you can do something like this. Pass the your java script value to the servlet/controller, do your processing and then pass this value to the jsp page by putting it into some object's as your requirement. Then you can use this value as you want.

Oracle - how to remove white spaces?

SELECT  REGEXP_REPLACE('A B_ __ kunjramansingh smartdude', '\s*', '')
FROM    dual

---
AB___kunjramansinghsmartdude

Update:

Just concatenate strings:

SELECT  a || b
FROM    mytable

How to select a record and update it, with a single queryset in Django?

only in a case in serializer things, you can update in very simple way!

my_model_serializer = MyModelSerializer(
    instance=my_model, data=validated_data)
if my_model_serializer.is_valid():

    my_model_serializer.save()

only in a case in form things!

instance = get_object_or_404(MyModel, id=id)
form = MyForm(request.POST or None, instance=instance)
if form.is_valid():
    form.save()

How to comment in Vim's config files: ".vimrc"?

A double quote to the left of the text you want to comment.

Example: " this is how a comment looks like in ~/.vimrc

Changing the cursor in WPF sometimes works, sometimes doesn't

Do you need the cursor to be a "wait" cursor only when it's over that particular page/usercontrol? If not, I'd suggest using Mouse.OverrideCursor:

Mouse.OverrideCursor = Cursors.Wait;
try
{
    // do stuff
}
finally
{
    Mouse.OverrideCursor = null;
}

This overrides the cursor for your application rather than just for a part of its UI, so the problem you're describing goes away.

Retrieve a single file from a repository

I use this

$ cat ~/.wgetrc
check_certificate = off

$ wget https://raw.github.com/jquery/jquery/master/grunt.js
HTTP request sent, awaiting response... 200 OK
Length: 11339 (11K) [text/plain]
Saving to: `grunt.js'

Could not reserve enough space for object heap to start JVM

It looks like the machine you're trying to run this on has only 256 MB memory.

Maybe the JVM tries to allocate a large, contiguous block of 64 MB memory. The 192 MB that you have free might be fragmented into smaller pieces, so that there is no contiguous block of 64 MB free to allocate.

Try starting your Java program with a smaller heap size, for example:

java -Xms16m ...

How to fix Error: this class is not key value coding-compliant for the key tableView.'

Any chance that you changed the name of your table view from "tableView" to "myTableView" at some point?

sqlplus error on select from external table: ORA-29913: error in executing ODCIEXTTABLEOPEN callout

When you want to create an external_table, all field's name must be written in UPPERCASE.

Done.

What is the "continue" keyword and how does it work in Java?

continue must be inside a loop Otherwise it showsThe error below:

Continue outside the loop

In Angular, I need to search objects in an array

Saw this thread but I wanted to search for IDs that did not match my search. Code to do that:

found = $filter('filter')($scope.fish, {id: '!fish_id'}, false);

html button to send email

This method doesn't seem to work in my browser, and looking around indicates that the whole subject of specifying headers to a mailto link/action is sparsely supported, but maybe this can help...

HTML:

<form id="fr1">
    <input type="text" id="tb1" />
    <input type="text" id="tb2" />
    <input type="button" id="bt1" value="click" />
</form>

JavaScript (with jQuery):

$(document).ready(function() {
    $('#bt1').click(function() {
        $('#fr1').attr('action',
                       'mailto:[email protected]?subject=' +
                       $('#tb1').val() + '&body=' + $('#tb2').val());
        $('#fr1').submit();
    });
});

Notice what I'm doing here. The form itself has no action associated with it. And the submit button isn't really a submit type, it's just a button type. Using JavaScript, I'm binding to that button's click event, setting the form's action attribute, and then submitting the form.

It's working in so much as it submits the form to a mailto action (my default mail program pops up and opens a new message to the specified address), but for me (Safari, Mail.app) it's not actually specifying the Subject or Body in the resulting message.

HTML isn't really a very good medium for doing this, as I'm sure others are pointing out while I type this. It's possible that this may work in some browsers and/or some mail clients. However, it's really not even a safe assumption anymore that users will have a fat mail client these days. I can't remember the last time I opened mine. HTML's mailto is a bit of legacy functionality and, these days, it's really just as well that you perform the mail action on the server-side if possible.

Working with SQL views in Entity Framework Core

Here is a new way to work with SQL views in EF Core: Query Types.

View a file in a different Git branch without changing branches

git show somebranch:path/to/your/file

you can also do multiple files and have them concatenated:

git show branchA~10:fileA branchB^^:fileB

You do not have to provide the full path to the file, relative paths are acceptable e.g.:

git show branchA~10:../src/hello.c

If you want to get the file in the local directory (revert just one file) you can checkout:

git checkout somebranch^^^ -- path/to/file

'tuple' object does not support item assignment

PIL pixels are tuples, and tuples are immutable. You need to construct a new tuple. So, instead of the for loop, do:

pixels = [(pixel[0] + 20, pixel[1], pixel[2]) for pixel in pixels]
image.putdata(pixels)

Also, if the pixel is already too red, adding 20 will overflow the value. You probably want something like min(pixel[0] + 20, 255) or int(255 * (pixel[0] / 255.) ** 0.9) instead of pixel[0] + 20.

And, to be able to handle images in lots of different formats, do image = image.convert("RGB") after opening the image. The convert method will ensure that the pixels are always (r, g, b) tuples.

MySQL - Select the last inserted row easiest way

In concurrency, the latest record may not be the record you just entered. It may better to get the latest record using the primary key.

If it is a auto increment field, use SELECT LAST_INSERT_ID(); to get the id you just created.

what is Segmentation fault (core dumped)?

"Segmentation fault" means that you tried to access memory that you do not have access to.

The first problem is with your arguments of main. The main function should be int main(int argc, char *argv[]), and you should check that argc is at least 2 before accessing argv[1].

Also, since you're passing in a float to printf (which, by the way, gets converted to a double when passing to printf), you should use the %f format specifier. The %s format specifier is for strings ('\0'-terminated character arrays).

TypeError: unhashable type: 'dict'

A possible solution might be to use the JSON dumps() method, so you can convert the dictionary to a string ---

import json

a={"a":10, "b":20}
b={"b":20, "a":10}
c = [json.dumps(a), json.dumps(b)]


set(c)
json.dumps(a) in c

Output -

set(['{"a": 10, "b": 20}'])
True

How to allow users to check for the latest app version from inside the app?

You can use this Android Library: https://github.com/danielemaddaluno/Android-Update-Checker. It aims to provide a reusable instrument to check asynchronously if exists any newer released update of your app on the Store. It is based on the use of Jsoup (http://jsoup.org/) to test if a new update really exists parsing the app page on the Google Play Store:

private boolean web_update(){
    try {       
        String curVersion = applicationContext.getPackageManager().getPackageInfo(package_name, 0).versionName; 
        String newVersion = curVersion;
        newVersion = Jsoup.connect("https://play.google.com/store/apps/details?id=" + package_name + "&hl=en")
                .timeout(30000)
                .userAgent("Mozilla/5.0 (Windows; U; WindowsNT 5.1; en-US; rv1.8.1.6) Gecko/20070725 Firefox/2.0.0.6")
                .referrer("http://www.google.com")
                .get()
                .select("div[itemprop=softwareVersion]")
                .first()
                .ownText();
        return (value(curVersion) < value(newVersion)) ? true : false;
    } catch (Exception e) {
        e.printStackTrace();
        return false;
    }
}

And as "value" function the following (works if values are beetween 0-99):

private long value(String string) {
    string = string.trim();
    if( string.contains( "." )){ 
        final int index = string.lastIndexOf( "." );
        return value( string.substring( 0, index ))* 100 + value( string.substring( index + 1 )); 
    }
    else {
        return Long.valueOf( string ); 
    }
}

If you want only to verify a mismatch beetween versions, you can change:

value(curVersion) < value(newVersion) with value(curVersion) != value(newVersion)

Removing duplicate characters from a string

As string is a list of characters, converting it to dictionary will remove all duplicates and will retain the order.

"".join(list(dict.fromkeys(foo)))

What is Gradle in Android Studio?

Short and simple answer for that,

Gradle is a build system, which is responsible for code compilation, testing, deployment and conversion of the code into . dex files and hence running the app on the device. As Android Studio comes with Gradle system pre-installed, there is no need to install additional runtime softwares to build our project.

VBA Object doesn't support this property or method

Object doesn't support this property or method.

Think of it like if anything after the dot is called on an object. It's like a chain.

An object is a class instance. A class instance supports some properties defined in that class type definition. It exposes whatever intelli-sense in VBE tells you (there are some hidden members but it's not related to this). So after each dot . you get intelli-sense (that white dropdown) trying to help you pick the correct action.

(you can start either way - front to back or back to front, once you understand how this works you'll be able to identify where the problem occurs)

Type this much anywhere in your code area

Dim a As Worksheets
a.

you get help from VBE, it's a little dropdown called Intelli-sense

enter image description here

It lists all available actions that particular object exposes to any user. You can't see the .Selection member of the Worksheets() class. That's what the error tells you exactly.

Object doesn't support this property or method.

If you look at the example on MSDN

Worksheets("GRA").Activate
iAreaCount = Selection.Areas.Count

It activates the sheet first then calls the Selection... it's not connected together because Selection is not a member of Worksheets() class. Simply, you can't prefix the Selection

What about

Sub DisplayColumnCount()
    Dim iAreaCount As Integer
    Dim i As Integer

    Worksheets("GRA").Activate
    iAreaCount = Selection.Areas.Count

    If iAreaCount <= 1 Then
        MsgBox "The selection contains " & Selection.Columns.Count & " columns."
    Else
        For i = 1 To iAreaCount
        MsgBox "Area " & i & " of the selection contains " & _
        Selection.Areas(i).Columns.Count & " columns."
        Next i
    End If
End Sub

from HERE

How to make Apache serve index.php instead of index.html?

PHP will work only on the .php file extension.

If you are on Apache you can also set, in your httpd.conf file, the extensions for PHP. You'll have to find the line:

AddType application/x-httpd-php .php .html
                                     ^^^^^

and add how many extensions, that should be read with the PHP interpreter, as you want.

Detecting when a div's height changes using jQuery

You can make a simple setInterval.

_x000D_
_x000D_
function someJsClass()_x000D_
{_x000D_
  var _resizeInterval = null;_x000D_
  var _lastHeight = 0;_x000D_
  var _lastWidth = 0;_x000D_
  _x000D_
  this.Initialize = function(){_x000D_
    var _resizeInterval = setInterval(_resizeIntervalTick, 200);_x000D_
  };_x000D_
  _x000D_
  this.Stop = function(){_x000D_
    if(_resizeInterval != null)_x000D_
      clearInterval(_resizeInterval);_x000D_
  };_x000D_
  _x000D_
  var _resizeIntervalTick = function () {_x000D_
    if ($(yourDiv).width() != _lastWidth || $(yourDiv).height() != _lastHeight) {_x000D_
      _lastWidth = $(contentBox).width();_x000D_
      _lastHeight = $(contentBox).height();_x000D_
      DoWhatYouWantWhenTheSizeChange();_x000D_
    }_x000D_
  };_x000D_
}_x000D_
_x000D_
var class = new someJsClass();_x000D_
class.Initialize();
_x000D_
_x000D_
_x000D_

EDIT:

This is a example with a class. But you can do something easiest.

List of special characters for SQL LIKE clause

Potential answer for SQL Server

Interesting I just ran a test using LinqPad with SQL Server which should be just running Linq to SQL underneath and it generates the following SQL statement.

Records .Where(r => r.Name.Contains("lkjwer--_~[]"))

-- Region Parameters
DECLARE @p0 VarChar(1000) = '%lkjwer--~_~~~[]%'
-- EndRegion
SELECT [t0].[ID], [t0].[Name]
FROM [RECORDS] AS [t0]
WHERE [t0].[Name] LIKE @p0 ESCAPE '~'

So I haven't tested it yet but it looks like potentially the ESCAPE '~' keyword may allow for automatic escaping of a string for use within a like expression.

Comparing two collections for equality irrespective of the order of items in them

Allowing for duplicates in the IEnumerable<T> (if sets are not desirable\possible) and "ignoring order" you should be able to use a .GroupBy().

I'm not an expert on the complexity measurements, but my rudimentary understanding is that this should be O(n). I understand O(n^2) as coming from performing an O(n) operation inside another O(n) operation like ListA.Where(a => ListB.Contains(a)).ToList(). Every item in ListB is evaluated for equality against each item in ListA.

Like I said, my understanding on complexity is limited, so correct me on this if I'm wrong.

public static bool IsSameAs<T, TKey>(this IEnumerable<T> source, IEnumerable<T> target, Expression<Func<T, TKey>> keySelectorExpression)
    {
        // check the object
        if (source == null && target == null) return true;
        if (source == null || target == null) return false;

        var sourceList = source.ToList();
        var targetList = target.ToList();

        // check the list count :: { 1,1,1 } != { 1,1,1,1 }
        if (sourceList.Count != targetList.Count) return false;

        var keySelector = keySelectorExpression.Compile();
        var groupedSourceList = sourceList.GroupBy(keySelector).ToList();
        var groupedTargetList = targetList.GroupBy(keySelector).ToList();

        // check that the number of grouptings match :: { 1,1,2,3,4 } != { 1,1,2,3,4,5 }
        var groupCountIsSame = groupedSourceList.Count == groupedTargetList.Count;
        if (!groupCountIsSame) return false;

        // check that the count of each group in source has the same count in target :: for values { 1,1,2,3,4 } & { 1,1,1,2,3,4 }
        // key:count
        // { 1:2, 2:1, 3:1, 4:1 } != { 1:3, 2:1, 3:1, 4:1 }
        var countsMissmatch = groupedSourceList.Any(sourceGroup =>
                                                        {
                                                            var targetGroup = groupedTargetList.Single(y => y.Key.Equals(sourceGroup.Key));
                                                            return sourceGroup.Count() != targetGroup.Count();
                                                        });
        return !countsMissmatch;
    }

Can't install Scipy through pip

The easiest way is in the following steps: Fixing scipy for python [ 2.n < python < 3.n ]

Download the necessary files from: http://www.lfd.uci.edu/~gohlke/pythonlibs/

Download the version of numpy+mkl (needed to run scipy) and then download scipy for your python type (2.n python written as 2n) or (3.n python written as 3n), n is a variable. Note you must know whether you have a 32bit or 64bit processor.

Create a directory somewhere on your computer, example [C:\DIRECTORY] to install the files numpy+mkd.whl and scipy.whl

Once both file are downloaded, find the location of the file on your computer and move it to the directory you created.

Example: First file installation is needed for scipy is in

C:\DIRECTORY\numpy\numpy-0.0.0+mkl-cp2n-cp2nm-win_amd32.whl

Example: Second file installation is in

C:\DIRECTORY\scipy\scipy-0.0.0-cp2n-cp2nm-win_amd32.whl

Go to your command prompt and proceed the following example for a python version 2.n:

py -2.n -m pip install C:\DIRECTORY\numpy\numpy-0.0.0+mkl-cp2n-cp2nm-win_amd32.whl

should install

py -2.n -m pip install C:\DIRECTORY\scipy\scipy-0.0.0-cp2n-cp2nm-win_amd32.whl

should install

Test both modules on your python IDLE as following:

import numpy

import scipy

the modules are working if no errors are returned.

IFDAAS

Deserialize JSON to ArrayList<POJO> using Jackson

You can deserialize directly to a list by using the TypeReference wrapper. An example method:

public static <T> T fromJSON(final TypeReference<T> type,
      final String jsonPacket) {
   T data = null;

   try {
      data = new ObjectMapper().readValue(jsonPacket, type);
   } catch (Exception e) {
      // Handle the problem
   }
   return data;
}

And is used thus:

final String json = "";
Set<POJO> properties = fromJSON(new TypeReference<Set<POJO>>() {}, json);

TypeReference Javadoc

Passing std::string by Value or Reference

I believe the normal answer is that it should be passed by value if you need to make a copy of it in your function. Pass it by const reference otherwise.

Here is a good discussion: http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/

What is the "Temporary ASP.NET Files" folder for?

The CLR uses it when it is compiling at runtime. Here is a link to MSDN that explains further.

How to get the filename without the extension from a path in Python?

Getting the name of the file without the extension:

import os
print(os.path.splitext("/path/to/some/file.txt")[0])

Prints:

/path/to/some/file

Documentation for os.path.splitext.

Important Note: If the filename has multiple dots, only the extension after the last one is removed. For example:

import os
print(os.path.splitext("/path/to/some/file.txt.zip.asc")[0])

Prints:

/path/to/some/file.txt.zip

See other answers below if you need to handle that case.

SQL Server 2008 R2 can't connect to local database in Management Studio

I know, this problem can be faced by so many people and many of them have uninstalled and re-installed the sql server for resolving this issue. In my observation the problem of not connecting the database service locally is just because of your network connection you are using, in most of the cases these problems will come when you are using wi-fi network.

Solution is, if you are using wi-fi then just right click on status of the network and get the ip details and enter the same ip in sql server name, it will work. Regards Vishwajeet

Select All as default value for Multivalue parameter

Does not work if you have nulls.

You can get around this by modifying your select statement to plop something into nulls:

phonenumber = CASE
  WHEN (isnull(phonenumber, '')='') THEN '(blank)'
  ELSE phonenumber
END

Centering FontAwesome icons vertically and horizontally

I just lowered the height to 28px on the .login-icon [class*='icon-'] Here's the fiddle: http://jsfiddle.net/mZHg7/

.login-icon [class*='icon-']{
    height: 28px;
    width: 50px;
    display: inline-block;
    text-align: center;
    vertical-align: baseline;
}

String replace method is not replacing characters

And when I debug this the logic does fall into the sentence.replace.

Yes, and then you discard the return value.

Strings in Java are immutable - when you call replace, it doesn't change the contents of the existing string - it returns a new string with the modifications. So you want:

sentence = sentence.replace("and", " ");

This applies to all the methods in String (substring, toLowerCase etc). None of them change the contents of the string.

Note that you don't really need to do this in a condition - after all, if the sentence doesn't contain "and", it does no harm to perform the replacement:

String sentence = "Define, Measure, Analyze, Design and Verify";
sentence = sentence.replace("and", " ");

How to add a new line in textarea element?

You might want to use \n instead of /n.

Convert date yyyyMMdd to system.datetime format

string time = "19851231";
DateTime theTime= DateTime.ParseExact(time,
                                        "yyyyMMdd",
                                        CultureInfo.InvariantCulture,
                                        DateTimeStyles.None);

PHP MySQL Google Chart JSON - Complete Example

Some might encounter this error (I got it while implementing PHP-MySQLi-JSON-Google Chart Example):

You called the draw() method with the wrong type of data rather than a DataTable or DataView.

The solution would be: replace jsapi and just use loader.js with:

google.charts.load('current', {packages: ['corechart']}) and 
google.charts.setOnLoadCallback 

-- according to the release notes --> The version of Google Charts that remains available via the jsapi loader is no longer being updated consistently. Please use the new gstatic loader from now on.

Create a circular button in BS3

Use font-awesome stacked icons (alternative to bootstrap badges). Here are more examples: http://fontawesome.io/examples/

_x000D_
_x000D_
 .no-border {_x000D_
        border: none;_x000D_
        background-color: white;_x000D_
        outline: none;_x000D_
        cursor: pointer;_x000D_
    }_x000D_
.color-no-focus {_x000D_
        color: grey;_x000D_
    }_x000D_
  .hover:hover {_x000D_
        color: blue;_x000D_
    }_x000D_
 .white {_x000D_
        color: white;_x000D_
    }
_x000D_
<button type="button" (click)="doSomething()" _x000D_
class="hover color-no-focus no-border fa-stack fa-lg">_x000D_
<i class="color-focus fa fa-circle fa-stack-2x"></i>_x000D_
<span class="white fa-stack-1x">1</span>_x000D_
</button>_x000D_
<link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet"/>
_x000D_
_x000D_
_x000D_

Bold & Non-Bold Text In A Single UILabel?

If you want to make using attributed strings easier, try using Attributed String Creator, which will generate the code for you. https://itunes.apple.com/us/app/attributed-string-creator/id730928349

C# function to return array

You're trying to return variable Labels of type ArtworkData instead of array, therefore this needs to be in the method signature as its return type. You need to modify your code as such:

public static ArtworkData[] GetDataRecords(int UsersID)
{
    ArtworkData[] Labels;
    Labels = new ArtworkData[3];

    return Labels;
}

Array[] is actually an array of Array, if that makes sense.

How to convert a Date to a formatted string in VB.net?

myDate.ToString("yyyy-MM-dd HH:mm:ss")

the capital HH is for 24 hours format as you specified

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoRestController'

Your DemoApplication class is in the com.ag.digital.demo.boot package and your LoginBean class is in the com.ag.digital.demo.bean package. By default components (classes annotated with @Component) are found if they are in the same package or a sub-package of your main application class DemoApplication. This means that LoginBean isn't being found so dependency injection fails.

There are a couple of ways to solve your problem:

  1. Move LoginBean into com.ag.digital.demo.boot or a sub-package.
  2. Configure the packages that are scanned for components using the scanBasePackages attribute of @SpringBootApplication that should be on DemoApplication.

A few of other things that aren't causing a problem, but are not quite right with the code you've posted:

  • @Service is a specialisation of @Component so you don't need both on LoginBean
  • Similarly, @RestController is a specialisation of @Component so you don't need both on DemoRestController
  • DemoRestController is an unusual place for @EnableAutoConfiguration. That annotation is typically found on your main application class (DemoApplication) either directly or via @SpringBootApplication which is a combination of @ComponentScan, @Configuration, and @EnableAutoConfiguration.

Property 'value' does not exist on type 'Readonly<{}>'

event.target is of type EventTarget which doesn't always have a value. If it's a DOM element you need to cast it to the correct type:

handleChange(event) {
    this.setState({value: (event.target as HTMLInputElement).value});
}

This will infer the "correct" type for the state variable as well though being explicit is probably better

Android - java.lang.SecurityException: Permission Denial: starting Intent

if we make the particular activity as

android:exported="true"

it will be the launching activity. Click on the module name just to the left of the run button and click on "Edit configurations..." Now make sure "Launch default Activity" is selected.

Create an array of integers property in Objective-C

This should work:

@interface MyClass
{
    int _doubleDigits[10]; 
}

@property(readonly) int *doubleDigits;

@end

@implementation MyClass

- (int *)doubleDigits
{
    return _doubleDigits;
}

@end

How can I check if character in a string is a letter? (Python)

This works:

any(c.isalpha() for c in 'string')

Passing an array by reference in C?

In C arrays are passed as a pointer to the first element. They are the only element that is not really passed by value (the pointer is passed by value, but the array is not copied). That allows the called function to modify the contents.

void reset( int *array, int size) {
   memset(array,0,size * sizeof(*array));
}
int main()
{
   int array[10];
   reset( array, 10 ); // sets all elements to 0
}

Now, if what you want is changing the array itself (number of elements...) you cannot do it with stack or global arrays, only with dynamically allocated memory in the heap. In that case, if you want to change the pointer you must pass a pointer to it:

void resize( int **p, int size ) {
   free( *p );
   *p = malloc( size * sizeof(int) );
}
int main() {
   int *p = malloc( 10 * sizeof(int) );
   resize( &p, 20 );
}

In the question edit you ask specifically about passing an array of structs. You have two solutions there: declare a typedef, or make explicit that you are passing an struct:

struct Coordinate {
   int x;
   int y;
};
void f( struct Coordinate coordinates[], int size );
typedef struct Coordinate Coordinate;  // generate a type alias 'Coordinate' that is equivalent to struct Coordinate
void g( Coordinate coordinates[], int size ); // uses typedef'ed Coordinate

You can typedef the type as you declare it (and it is a common idiom in C):

typedef struct Coordinate {
   int x;
   int y;
} Coordinate;

Why use a READ UNCOMMITTED isolation level?

This isolation level allows dirty reads. One transaction may see uncommitted changes made by some other transaction.

To maintain the highest level of isolation, a DBMS usually acquires locks on data, which may result in a loss of concurrency and a high locking overhead. This isolation level relaxes this property.

You may want to check out the Wikipedia article on READ UNCOMMITTED for a few examples and further reading.


You may also be interested in checking out Jeff Atwood's blog article on how he and his team tackled a deadlock issue in the early days of Stack Overflow. According to Jeff:

But is nolock dangerous? Could you end up reading invalid data with read uncommitted on? Yes, in theory. You'll find no shortage of database architecture astronauts who start dropping ACID science on you and all but pull the building fire alarm when you tell them you want to try nolock. It's true: the theory is scary. But here's what I think: "In theory there is no difference between theory and practice. In practice there is."

I would never recommend using nolock as a general "good for what ails you" snake oil fix for any database deadlocking problems you may have. You should try to diagnose the source of the problem first.

But in practice adding nolock to queries that you absolutely know are simple, straightforward read-only affairs never seems to lead to problems... As long as you know what you're doing.

One alternative to the READ UNCOMMITTED level that you may want to consider is the READ COMMITTED SNAPSHOT. Quoting Jeff again:

Snapshots rely on an entirely new data change tracking method ... more than just a slight logical change, it requires the server to handle the data physically differently. Once this new data change tracking method is enabled, it creates a copy, or snapshot of every data change. By reading these snapshots rather than live data at times of contention, Shared Locks are no longer needed on reads, and overall database performance may increase.

Android - drawable with rounded corners at the top only

Try giving these values:

 <corners android:topLeftRadius="6dp" android:topRightRadius="6dp"
         android:bottomLeftRadius="0.1dp" android:bottomRightRadius="0.1dp"/>

Note that I have changed 0dp to 0.1dp.

EDIT: See Aleks G comment below for a cleaner version

Python: TypeError: object of type 'NoneType' has no len()

What is the purpose of this

 names = list;

? Also, no ; required in Python.

Do you want

 names = []

or

 names = list()

at the start of your program instead? Though given your particular code, there's no need for this statement to create this names variable since you do so later when you read data into it from your file.

@JBernardo has already pointed out the other (and more major) problem with the code.