Programs & Examples On #Linq to sql

LINQ to SQL is a component of .NET Framework version 3.5 that provides a run-time infrastructure for managing relational data as objects stored in Microsoft SQL Server.

System.Data.SqlClient.SqlException: Invalid object name 'dbo.Projects'

If you use two databases you can add another DataClasses.dbml and map the second database into it.
It works.

How to select only the records with the highest date in LINQ

If you want the whole record,here is a lambda way:

var q = _context
             .GroupBy(s => s.AccountId)
             .Select(s => s.OrderByDescending(x => x.Date).FirstOrDefault());

Difference Between Select and SelectMany

The SelectMany() method is used to flatten a sequence in which each of the elements of the sequence is a separate.

I have class user same like this

class User
        public string UserName { get; set; }
        public List<string> Roles { get; set; }


var users = new List<User>
                new User { UserName = "Reza" , Roles = new List<string>{"Superadmin" } },
                new User { UserName = "Amin" , Roles = new List<string>{"Guest","Reseption" } },
                new User { UserName = "Nima" , Roles = new List<string>{"Nurse","Guest" } },

var query = users.SelectMany(user => user.Roles, (user, role) => new { user.UserName, role });

foreach (var obj in query)

//{ UserName = Reza, role = Superadmin }
//{ UserName = Amin, role = Guest }
//{ UserName = Amin, role = Reseption }
//{ UserName = Nima, role = Nurse }
//{ UserName = Nima, role = Guest }

You can use operations on any item of sequence

int[][] numbers = {
                new[] {1, 2, 3},
                new[] {4},
                new[] {5, 6 , 6 , 2 , 7, 8},
                new[] {12, 14}

IEnumerable<int> result = numbers
                .SelectMany(array => array.Distinct())
                .OrderBy(x => x);


//{ 1, 2 , 2 , 3, 4, 5, 6, 7, 8, 12, 14 }
 List<List<int>> numbers = new List<List<int>> {
                new List<int> {1, 2, 3},
                new List<int> {12},
                new List<int> {5, 6, 5, 7},
                new List<int> {10, 10, 10, 12}

 IEnumerable<int> result = numbers
                .SelectMany(list => list)


// { 1, 2, 3, 5, 6, 7, 10, 12 }

What is the syntax for an inner join in LINQ to SQL?

from d1 in DealerContrac join d2 in DealerContrac on d1.dealearid equals d2.dealerid select new {dealercontract.*}

LINQ-to-SQL vs stored procedures?

IMHO, RAD = LINQ, RUP = Stored Procs. I worked for a large Fortune 500 company for many years, at many levels including management, and frankly, I would never hire RUP developers to do RAD development. They are so siloed that they very limited knowledge of what to do at other levels of the process. With a siloed environment, it makes sense to give DBAs control over the data through very specific entry points, because others frankly don't know the best ways to accomplish data management.

But large enterprises move painfully slow in the development arena, and this is extremely costly. There are times when you need to move faster to save both time and money, and LINQ provides that and more in spades.

Sometimes I think that DBAs are biased against LINQ because they feel it threatens their job security. But that's the nature of the beast, ladies and gentlemen.

Linq to Sql: Multiple left outer joins

This may be cleaner (you dont need all the into statements):

var query = 
    from order in dc.Orders
    from vendor 
    in dc.Vendors
        .Where(v => v.Id == order.VendorId)
    from status 
    in dc.Status
        .Where(s => s.Id == order.StatusId)
    select new { Order = order, Vendor = vendor, Status = status } 
    //Vendor and Status properties will be null if the left join is null

Here is another left join example

var results = 
    from expense in expenseDataContext.ExpenseDtos
    where expense.Id == expenseId //some expense id that was passed in
    from category 
    // left join on categories table if exists
    in expenseDataContext.CategoryDtos
                         .Where(c => c.Id == expense.CategoryId)
    // left join on expense type table if exists
    from expenseType 
    in expenseDataContext.ExpenseTypeDtos
                         .Where(e => e.Id == expense.ExpenseTypeId)
    // left join on currency table if exists
    from currency 
    in expenseDataContext.CurrencyDtos
                         .Where(c => c.CurrencyID == expense.FKCurrencyID)
    select new 
        Expense = expense,
        // category will be null if join doesn't exist
        Category = category,
        // expensetype will be null if join doesn't exist
        ExpenseType = expenseType,
        // currency will be null if join doesn't exist
        Currency = currency  

LINQ to SQL - Left Outer Join with multiple join conditions

I know it's "a bit late" but just in case if anybody needs to do this in LINQ Method syntax (which is why I found this post initially), this would be how to do that:

var results = context.Periods
        period =>,
        fk => fk.periodid,
        (period, fact) => fact.Where(f => f.otherid == 17)

Update using LINQ to SQL

I found a workaround a week ago. You can use direct commands with "ExecuteCommand":

MDataContext dc = new MDataContext();
var flag = (from f in dc.Flags
                   where f.Code == Code
                   select f).First();
_refresh = Convert.ToBoolean(flagRefresh.Value);
if (_refresh)
    dc.ExecuteCommand("update Flags set value = 0 where code = {0}", Code);

In the ExecuteCommand statement, you can send the query directly, with the value for the specific record you want to update.

value = 0 --> 0 is the new value for the record;

code = {0} --> is the field where you will send the filter value;

Code --> is the new value for the field;

I hope this reference helps.

Return anonymous type results?

Try this to get dynamic data. You can convert code for List<>

public object GetDogsWithBreedNames()
    var db = new DogDataContext(ConnectString);
    var result = from d in db.Dogs
                 join b in db.Breeds on d.BreedId equals b.BreedId
                 select new
                            Name = d.Name,
                            BreedName = b.BreedName
    return result.FirstOrDefault();

dynamic dogInfo=GetDogsWithBreedNames();
var name = dogInfo.GetType().GetProperty("Name").GetValue(dogInfo, null);
var breedName = dogInfo.GetType().GetProperty("BreedName").GetValue(dogInfo, null);

Linq to SQL how to do "where [column] in (list of values)"


where list.Contains(item.Property)

Or in your case:

var foo = from codeData in channel.AsQueryable<CodeData>()
          where codeIDs.Contains(codeData.CodeId)
          select codeData;

But you might as well do that in dot notation:

var foo = channel.AsQueryable<CodeData>()
                 .Where(codeData => codeIDs.Contains(codeData.CodeId));

Entity Framework vs LINQ to SQL


  1. Homogeneous datasource: SQL Server
  2. Recommended for small projects only where data structure is well designed
  3. Mapping can be changed without recompilling with SqlMetal.exe
  4. .dbml (Database Markup Language)
  5. One-to-one mapping between tables and classes
  6. Supports TPH inheritance
  7. Doesn't support complex types
  8. Storage-first approach
  9. Database-centric view of a database
  10. Created by C# team
  11. Supported but not further improvements intended

Entity Framework

  1. Heterogeneus datasource: Support many data providers
  2. Recommended for all new projects except:
    • small ones (LINQ to SQL)
    • when data source is a flat file (ADO.NET)
  3. Mapping can be changed without recompilling when setting model and mapping files Metadata Artifact Process to Copy To Output Directory
  4. .edmx (Entity Data Model) which contains:
    • SSDL (Storage Schema Definition Language)
    • CSDL (Conceptual Schema Definition Language)
    • MSL (Mapping Specification Language)
  5. One-to-one, one-to-many, many-to-one mappings between tables and classes
  6. Supports inheritence:
    • TPH (Table Per Hierarchy)
    • TPT (Table Per Type)
    • TPC (Table Per Concrete Class)
  7. Supports complex types
  8. Code-first, Model-first, Storage-first approaches
  9. Application-centric view of a database
  10. Created by SQL Server team
  11. Future of Microsoft Data APIs

See also:

LINQ to SQL: Multiple joins ON multiple Columns. Is this possible?

You can write your query like this.

var query = from t1 in myTABLE1List // List<TABLE_1>
            join t2 in myTABLE1List
               on t1.ColumnA equals t2.ColumnA
               and t1.ColumnB equals t2.ColumnA

If you want to compare your column with multiple columns.

efficient way to implement paging

While LINQ-to-SQL will generate an OFFSET clause (possibly emulated using ROW_NUMBER() OVER() as others have mentioned), there is an entirely different, much faster way to perform paging in SQL. This is often called the "seek method" as described in this blog post here.

SELECT TOP 10 first_name, last_name, score
FROM players
WHERE (score < @previousScore)
   OR (score = @previousScore AND player_id < @previousPlayerId)
ORDER BY score DESC, player_id DESC

The @previousScore and @previousPlayerId values are the respective values of the last record from the previous page. This allows you to fetch the "next" page. If the ORDER BY direction is ASC, simply use > instead.

With the above method, you cannot immediately jump to page 4 without having first fetched the previous 40 records. But often, you do not want to jump that far anyway. Instead, you get a much faster query that might be able to fetch data in constant time, depending on your indexing. Plus, your pages remain "stable", no matter if the underlying data changes (e.g. on page 1, while you're on page 4).

This is the best way to implement paging when lazy loading more data in web applications, for instance.

Note, the "seek method" is also called keyset paging.

Multiple WHERE clause in Linq

Also, you can use bool method(s)

Query :

DataTable tempData = (DataTable)grdUsageRecords.DataSource;
var query = from r in tempData.AsEnumerable()
            where isValid(Field<string>("UserName"))// && otherMethod() && otherMethod2()                           
            select r;   

        DataTable newDT = query.CopyToDataTable();


bool isValid(string userName)
    if(userName == "XXXX" || userName == "YYYY")
        return false;
    else return true;

LINQ to SQL - How to select specific columns and return strongly typed list

Make a call to the DB searching with myid (Id of the row) and get back specific columns:

var columns = db.Notifications
                .Where(x => x.Id == myid)
                .Select(n => new { n.NotificationTitle, 
                                   n.NotificationOrder });

LINQ Where with AND OR condition

from item in db.vw_Dropship_OrderItems
    where (listStatus != null ? listStatus.Contains(item.StatusCode) : true) &&
    (listMerchants != null ? listMerchants.Contains(item.MerchantId) : true)
    select item;

Might give strange behavior if both listMerchants and listStatus are both null.

LINQ - Left Join, Group By, and Count

from p in context.ParentTable
join c in context.ChildTable on p.ParentId equals c.ChildParentId into j1
from j2 in j1.DefaultIfEmpty()
group j2 by p.ParentId into grouped
select new { ParentId = grouped.Key, Count = grouped.Count(t=>t.ChildId != null) }

Entity Framework VS LINQ to SQL VS ADO.NET with stored procedures?

LINQ-to-SQL is a remarkable piece of technology that is very simple to use, and by and large generates very good queries to the back end. LINQ-to-EF was slated to supplant it, but historically has been extremely clunky to use and generated far inferior SQL. I don't know the current state of affairs, but Microsoft promised to migrate all the goodness of L2S into L2EF, so maybe it's all better now.

Personally, I have a passionate dislike of ORM tools (see my diatribe here for the details), and so I see no reason to favour L2EF, since L2S gives me all I ever expect to need from a data access layer. In fact, I even think that L2S features such as hand-crafted mappings and inheritance modeling add completely unnecessary complexity. But that's just me. ;-)

How do you perform a left outer join using linq extension methods

For a (left outer) join of a table Bar with a table Foo on Foo.Foo_Id = Bar.Foo_Id in lambda notation:

var qry = Foo.GroupJoin(
          foo => foo.Foo_Id,
          bar => bar.Foo_Id,
          (x,y) => new { Foo = x, Bars = y })
           x => x.Bars.DefaultIfEmpty(),
           (x,y) => new { Foo=x.Foo, Bar=y});

Returning IEnumerable<T> vs. IQueryable<T>

There is a blog post with brief source code sample about how misuse of IEnumerable<T> can dramatically impact LINQ query performance: Entity Framework: IQueryable vs. IEnumerable.

If we dig deeper and look into the sources, we can see that there are obviously different extension methods are perfomed for IEnumerable<T>:

// Type: System.Linq.Enumerable
// Assembly: System.Core, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089
// Assembly location: C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Core.dll
public static class Enumerable
    public static IEnumerable<TSource> Where<TSource>(
        this IEnumerable<TSource> source, 
        Func<TSource, bool> predicate)
        return (IEnumerable<TSource>) 
            new Enumerable.WhereEnumerableIterator<TSource>(source, predicate);

and IQueryable<T>:

// Type: System.Linq.Queryable
// Assembly: System.Core, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089
// Assembly location: C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Core.dll
public static class Queryable
    public static IQueryable<TSource> Where<TSource>(
        this IQueryable<TSource> source, 
        Expression<Func<TSource, bool>> predicate)
        return source.Provider.CreateQuery<TSource>(
                ((MethodInfo) MethodBase.GetCurrentMethod()).MakeGenericMethod(
                    new Type[] { typeof(TSource) }), 
                    new Expression[] 
                        { source.Expression, Expression.Quote(predicate) }));

The first one returns enumerable iterator, and the second one creates query through the query provider, specified in IQueryable source.

How do I update a Linq to SQL dbml file?

There are three ways to keep the model in sync.

  1. Delete the modified tables from the designer, and drag them back onto the designer surface from the Database Explorer. I have found that, for this to work reliably, you have to:

    a. Refresh the database schema in the Database Explorer (right-click, refresh)
    b. Save the designer after deleting the tables
    c. Save again after dragging the tables back.

    Note though that if you have modified any properties (for instance, turning off the child property of an association), this will obviously lose those modifications — you'll have to make them again.

  2. Use SQLMetal to regenerate the schema from your database. I have seen a number of blog posts that show how to script this.

  3. Make changes directly in the Properties pane of the DBML. This works for simple changes, like allowing nulls on a field.

The DBML designer is not installed by default in Visual Studio 2015, 2017 or 2019. You will have to close VS, start the VS installer and modify your installation. The LINQ to SQL tools is the feature you must install. For VS 2017/2019, you can find it under Individual Components > Code Tools.

How to do a subquery in LINQ?

Here's a subquery for you!

List<int> IdsToFind = new List<int>() {2, 3, 4};

.Where(u => SqlMethods.Like(u.LastName, "%fra%"))
.Where(u =>
    .Where(crtu => IdsToFind.Contains(crtu.CompanyRoleId))
    .Select(crtu =>  crtu.UserId)

Regarding this portion of the question:

predicateAnd = predicateAnd.And(c => c.LastName.Contains(

I strongly recommend extracting the string from the textbox before authoring the query.

string searchString = TextBoxLastName.Text.Trim();
predicateAnd = predicateAnd.And(c => c.LastName.Contains( searchString));

You want to maintain good control over what gets sent to the database. In the original code, one possible reading is that an untrimmed string gets sent into the database for trimming - which is not good work for the database to be doing.

Error - SqlDateTime overflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM

Sometimes in order to write less code it is used to have SQL server set fields like date, time and ID on insert by setting the default value for fields to GETDATE() or NEWID().

In such cases Auto Generated Value property of those fields in entity classes should be set to true.

This way you do not need to set values in code (preventing energy consumption!!!) and never see that exception.

how to update the multiple rows at a time using linq to sql?

Do not use the ToList() method as in the accepted answer !

Running SQL profiler, I verified and found that ToList() function gets all the records from the database. It is really bad performance !!

I would have run this query by pure sql command as follows:

string query = "Update YourTable Set ... Where ...";    
context.Database.ExecuteSqlCommandAsync(query, new SqlParameter("@ColumnY", value1), new SqlParameter("@ColumnZ", value2));

This would operate the update in one-shot without selecting even one row.

What's the Linq to SQL equivalent to TOP or LIMIT/OFFSET?

Use the Take(int n) method:

var q = query.Take(10);

LINQ syntax where string value is not null or empty

Problem Statement
It's possible to write LINQ to SQL that gets all rows that have either null or an empty string in a given field, but it's not possible to use string.IsNullOrEmpty to do it, even though many other string methods map to LINQ to SQL. Proposed Solution Allow string.IsNullOrEmpty in a LINQ to SQL where clause so that these two queries have the same result:

var fieldNullOrEmpty =
from item in db.SomeTable
where item.SomeField == null || item.SomeField.Equals(string.Empty)
select item;

var fieldNullOrEmpty2 =
from item in db.SomeTable
where string.IsNullOrEmpty(item.SomeField)
select item;

Other Reading:
1. DevArt
3. StackOverflow Post

Convert Linq Query Result to Dictionary

Use namespace

using System.Collections.Specialized;

Make instance of DataContext Class

LinqToSqlDataContext dc = new LinqToSqlDataContext();


OrderedDictionary dict = dc.TableName.ToDictionary(d => d.key, d => d.value);

In order to retrieve the values use namespace

   using System.Collections;

ICollection keyCollections = dict.Keys;
ICOllection valueCollections = dict.Values;

String[] myKeys = new String[dict.Count];
String[] myValues = new String[dict.Count];


for(int i=0; i<dict.Count; i++)
Console.WriteLine("Key: " + myKeys[i] + "Value: " + myValues[i]);

How to do a join in linq to sql with method syntax?

To add on to the other answers here, if you would like to create a new object of a third different type with a where clause (e.g. one that is not your Entity Framework object) you can do this:

public IEnumerable<ThirdNonEntityClass> demoMethod(IEnumerable<int> property1Values)
    using(var entityFrameworkObjectContext = new EntityFrameworkObjectContext )
        var result = entityFrameworkObjectContext.SomeClass
                sc => sc.property1,
                soc => soc.property2,
                (sc, soc) => new {sc, soc})
            .Where(s => propertyValues.Any(pvals => pvals ==
            .Select(s => new ThirdNonEntityClass 
                dataValue1 =,
                dataValue2 = s.soc.dataValueB

    return result;


Pay special attention to the intermediate object that is created in the Where and Select clauses.

Note that here we also look for any joined objects that have a property1 that matches one of the ones in the input list.

I know this is a bit more complex than what the original asker was looking for, but hopefully it will help someone.

How to store a list in a column of a database table

In addition to what everyone else has said, I would suggest you analyze your approach in longer terms than just now. It is currently the case that items are unique. It is currently the case that resorting the items would require a new list. It is almost required that the list are currently short. Even though I don't have the domain specifics, it is not much of a stretch to think those requirements could change. If you serialize your list, you are baking in an inflexibility that is not necessary in a more-normalized design. Btw, that does not necessarily mean a full Many:Many relationship. You could just have a single child table with a foreign key to the parent and a character column for the item.

If you still want to go down this road of serializing the list, you might consider storing the list in XML. Some databases such as SQL Server even have an XML data type. The only reason I'd suggest XML is that almost by definition, this list needs to be short. If the list is long, then serializing it in general is an awful approach. If you go the CSV route, you need to account for the values containing the delimiter which means you are compelled to use quoted identifiers. Persuming that the lists are short, it probably will not make much difference whether you use CSV or XML.

How to compare only Date without Time in DateTime types in Linq to SQL with Entity Framework?

DateTime dt1 = DateTime.Now.Date;
DateTime dt2 = Convert.ToDateTime(TextBox4.Text.Trim()).Date;
if (dt1 >= dt2)
    MessageBox.Show("Valid Date");
    MessageBox.Show("Invalid Date... Please Give Correct Date....");

Linq to SQL .Sum() without group ... into



Actually this would perform better:

var itemsInCart = from o in db.OrderLineItems
              where o.OrderId == currentOrder.OrderId
              select new { o.WishListItem.Price };
var sum = itemsCard.ToList().Select(c=>c.Price).Sum();

Because you'll only be retrieving one column from the database.


This is how you do a distinct count query. Note that you have to filter out the nulls.

var useranswercount = (from a in tpoll_answer
where user_nbr != null && answer_nbr != null
select user_nbr).Distinct().Count();

If you combine this with into your current grouping code, I think you'll have your solution.

Understanding SQL Server LOCKS on SELECT queries

At my work, we have a very big system that runs on many PCs at the same time, with very big tables with hundreds of thousands of rows, and sometimes many millions of rows.

When you make a SELECT on a very big table, let's say you want to know every transaction a user has made in the past 10 years, and the primary key of the table is not built in an efficient way, the query might take several minutes to run.

Then, our application might me running on many user's PCs at the same time, accessing the same database. So if someone tries to insert into the table that the other SELECT is reading (in pages that SQL is trying to read), then a LOCK can occur and the two transactions block each other.

We had to add a "NO LOCK" to our SELECT statement, because it was a huge SELECT on a table that is used a lot by a lot of users at the same time and we had LOCKS all the time.

I don't know if my example is clear enough? This is a real life example.

LINQ: When to use SingleOrDefault vs. FirstOrDefault() with filtering criteria

I queried Google for the usage of the different methods on GitHub. This is done by running a Google search query for each method and limiting the query to the domain and the .cs file extension by using the query " file:cs ..."

It seems that the First* methods are more commonly used than the Single* methods.

| Method               | Results |
| FirstAsync           |     315 |
| SingleAsync          |     166 |
| FirstOrDefaultAsync  |     357 |
| SingleOrDefaultAsync |     237 |
| FirstOrDefault       |   17400 |
| SingleOrDefault      |    2950 |

LINQ to SQL Left Outer Join

You don't need the into statements:

var query = 
    from customer in dc.Customers
    from order in dc.Orders
         .Where(o => customer.CustomerId == o.CustomerId)
    select new { Customer = customer, Order = order } 
    //Order will be null if the left join is null

And yes, the query above does indeed create a LEFT OUTER join.

Link to a similar question that handles multiple left joins: Linq to Sql: Multiple left outer joins

How to do Select All(*) in linq to sql

Why don't you use

DbTestDataContext obj = new DbTestDataContext();
var q =from a in obj.GetTable<TableName>() select a;

This is simple.

Can I return the 'id' field after a LINQ insert?

When inserting the generated ID is saved into the instance of the object being saved (see below):

protected void btnInsertProductCategory_Click(object sender, EventArgs e)
  ProductCategory productCategory = new ProductCategory();
  productCategory.Name = “Sample Category”;
  productCategory.ModifiedDate = DateTime.Now;
  productCategory.rowguid = Guid.NewGuid();
  int id = InsertProductCategory(productCategory);
  lblResult.Text = id.ToString();

//Insert a new product category and return the generated ID (identity value)
private int InsertProductCategory(ProductCategory productCategory)
  return productCategory.ProductCategoryID;


LINQ: combining join and group by

I met the same problem as you.

I push two tables result into t1 object and group t1.

 from p in Products                         
  join bp in BaseProducts on p.BaseProductId equals bp.Id
  select new {
  } into t1
 group t1 by t1.p.SomeId into g
 select new ProductPriceMinMax { 
  SomeId = g.FirstOrDefault().p.SomeId, 
  CountryCode = g.FirstOrDefault().p.CountryCode, 
  MinPrice = g.Min(m => m.bp.Price), 
  MaxPrice = g.Max(m => m.bp.Price),
  BaseProductName = g.FirstOrDefault().bp.Name

How to do a LIKE query with linq?

Try using string.Contains () combined with EndsWith.

var results = from c in db.Customers
              where c.FullName.Contains (FirstName) && c.FullName.EndsWith (LastName)
              select c;

How do I get the MAX row with a GROUP BY in LINQ query?

This can be done using GroupBy and SelectMany in LINQ lamda expression

var groupByMax = list.GroupBy(x=>x.item1).SelectMany(y=>y.Where(z=>z.item2 == y.Max(i=>i.item2)));

How to Select Min and Max date values in Linq Query

This should work for you

//Retrieve Minimum Date
var MinDate = (from d in dataRows select d.Date).Min();

//Retrieve Maximum Date
var MaxDate = (from d in dataRows select d.Date).Max(); 

(From here)

If Else in LINQ

I assume from db that this is LINQ-to-SQL / Entity Framework / similar (not LINQ-to-Objects);

Generally, you do better with the conditional syntax ( a ? b : c) - however, I don't know if it will work with your different queries like that (after all, how would your write the TSQL?).

For a trivial example of the type of thing you can do:

select new {p.PriceID, Type = p.Price > 0 ? "debit" : "credit" };

You can do much richer things, but I really doubt you can pick the table in the conditional. You're welcome to try, of course...

Max or Default?

Since DefaultIfEmpty isn't implemented in LINQ to SQL, I did a search on the error it returned and found a fascinating article that deals with null sets in aggregate functions. To summarize what I found, you can get around this limitation by casting to a nullable within your select. My VB is a little rusty, but I think it'd go something like this:

Dim x = (From y In context.MyTable _
         Where y.MyField = value _
         Select CType(y.MyCounter, Integer?)).Max

Or in C#:

var x = (from y in context.MyTable
         where y.MyField == value
         select (int?)y.MyCounter).Max();

"getaddrinfo failed", what does that mean?

The problem in my case was that I needed to add environment variables for http_proxy and https_proxy.



To set these environment variables in Windows, see the answers to this question.

How to cherry pick a range of commits and merge into another branch?

git cherry-pick FIRST^..LAST works only for simple scenarios.

To achieve a decent "merge it into the integration branch" while having the usal comfort with things like auto-skipping of already integrated picks, transplanting diamond-merges, interactive control ...) better use a rebase. One answer here pointed to that, however the protocol included a dicey git branch -f and a juggling with a temp branch. Here a straight robust method:

git rebase -i FIRST LAST~0 --onto integration
git rebase @ integration

The -i allows for interactive control. The ~0 ensures a detached rebase (not moving the / another branch) in case LAST is a branch name. It can be omitted otherwise. The second rebase command just moves the integration branch ref in safe manner forward to the intermediate detached head - it doesn't introduce new commits. To rebase a complex structure with merge diamonds etc. consider --rebase-merges or --rebase-merges=rebase-cousins in the first rebase.

How to convert entire dataframe to numeric while preserving decimals?

df2 <- data.frame(apply(df1, 2, function(x) as.numeric(as.character(x))))

Basic authentication for REST API using spring restTemplate

Instead of instantiating as follows:

TestRestTemplate restTemplate = new TestRestTemplate();

Just do it like this:

TestRestTemplate restTemplate = new TestRestTemplate(user, password);

It works for me, I hope it helps!

getting integer values from textfield

You need to use Integer.parseInt(String)

private void jTextField2MouseClicked(java.awt.event.MouseEvent evt) {
            int jml = Integer.parseInt(jTextField3.getText());


How are software license keys generated?

All of the CD only copy protection algorithms inconvience honest users while providing no protection against piracy whatsoever.

The "pirate" only need to have access to one legitimate cd and its access code, he can then make n copies and distribute them.

It does not matter how cryptographically secure you make the code, you need to supply this with the CD in plain text or an legitimate user cannot activite the software.

Most secure schemes involve either the user providing the software supplier with some details of the machine which will run the software (cpu serial numbers, mac addresses, Ip address etc.), or, require online access to register the software on the suppliers website and in return receive an activitation token. The first option requires a lot of manual administration and is only worth it for very high value software, the, second option can be spoofed and is absolutly infuriating if you have limited network access or you are stuck behind a firewall.

On the whole its much easier to establish a trust relationship with your customers!

Difference between JOIN and INNER JOIN

No, there is no difference, pure syntactic sugar.

Install-Module : The term 'Install-Module' is not recognized as the name of a cmdlet

You should install the latest version of PowerShell, then use this command Install-Module Azure to install azure module. Because from Powershell 5.0 onwards you , you will be able to use the cmdlet to Install-Module, Save-Module

PS > $psversiontable
Name                           Value
----                           -----
PSVersion                      5.1.14393.576
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.14393.576
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3

More information about install Azure PowerShell, refer to the link.

oracle.jdbc.driver.OracleDriver ClassNotFoundException


This line causes ClassNotFoundException, because you haven't placed ojdbc14.jar file in your lib folder of the project. or YOu haven't set the classpath of the required jar

Selecting an element in iFrame jQuery

when your document is ready that doesn't mean that your iframe is ready too,
so you should listen to the iframe load event then access your contents:

$(function() {
        $(this).contents().find("[tokenid=" + token + "]").html();

JQuery Find #ID, RemoveClass and AddClass

corrected Code:


How to copy marked text in notepad++

It would be a great feature to have in Notepad++. I use the following technique to extract all the matches out of a file:

select-string -Path input.txt -Pattern "[0-9a-zA-Z ]*" -AllMatches | % { $_.Matches } | select-object Value > output.txt

And if you'd like only the distinct matches in a sorted list:

select-string -Path input.txt -Pattern "[0-9a-zA-Z ]" -AllMatches | % { $_.Matches } | select-object Value -unique | sort-object Value > output.txt

Define a fixed-size list in Java

If you want some flexibility, create a class that watches the size of the list.

Here's a simple example. You would need to override all the methods that change the state of the list.

public class LimitedArrayList<T> extends ArrayList<T>{
    private int limit;

    public LimitedArrayList(int limit){
        this.limit = limit;

    public void add(T item){
        if (this.size() > limit)
            throw new ListTooLargeException();

    // ... similarly for other methods that may add new elements ...

Working Copy Locked

Every time I get a Working copy locked error I run a "Clean up". After that everything is back to normal.

On the command line you can execute svn cleanup which also removes lock files.

Note: Perform this operation on one level up directory and that should resolve most of the times.

Understanding INADDR_ANY for socket programming

INADDR_ANY is used when you don't need to bind a socket to a specific IP. When you use this value as the address when calling bind(), the socket accepts connections to all the IPs of the machine.

How to get element's width/height within directives and component?

For a bit more flexibility than with micronyks answer, you can do it like that:

1. In your template, add #myIdentifier to the element you want to obtain the width from. Example:

<p #myIdentifier>
  my-component works!

2. In your controller, you can use this with @ViewChild('myIdentifier') to get the width:

import {AfterViewInit, Component, ElementRef, OnInit, ViewChild} from '@angular/core';

  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.scss']
export class MyComponentComponent implements AfterViewInit {

  constructor() { }

  ngAfterViewInit() {

  myIdentifier: ElementRef;



About the security risk with ElementRef, like this, there is none. There would be a risk, if you would modify the DOM using an ElementRef. But here you are only getting DOM Elements so there is no risk. A risky example of using ElementRef would be: this.myIdentifier.nativeElement.onclick = someFunctionDefinedBySomeUser;. Like this Angular doesn't get a chance to use its sanitisation mechanisms since someFunctionDefinedBySomeUser is inserted directly into the DOM, skipping the Angular sanitisation.

Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays

For anyone else with this issue that arrives here via Google, please check that the host element of the *ngFor directive is accurate. By this, I mean that I encountered this error and spent a long time researching fixes before realizing that I had put the *ngFor on an ng-template element instead of on my component I wanted to repeat.


<ng-template *ngFor=let group of groups$ | async" ...>
  <my-component [prop1]="group.key" ... </my-component>


<my-component *ngFor=let group of groups$ | async" [prop1]="group.key" ... </my-component>

I know this is an obvious mistake in hindsight, but I hope an answer here will save someone the headache I now have.

How to select the last record from MySQL table using SQL syntax

User order by with desc order:

select * from t
order by id desc
limit 1

Declare an array in TypeScript

Here are the different ways in which you can create an array of booleans in typescript:

let arr1: boolean[] = [];
let arr2: boolean[] = new Array();
let arr3: boolean[] = Array();

let arr4: Array<boolean> = [];
let arr5: Array<boolean> = new Array();
let arr6: Array<boolean> = Array();

let arr7 = [] as boolean[];
let arr8 = new Array() as Array<boolean>;
let arr9 = Array() as boolean[];

let arr10 = <boolean[]> [];
let arr11 = <Array<boolean>> new Array();
let arr12 = <boolean[]> Array();

let arr13 = new Array<boolean>();
let arr14 = Array<boolean>();

You can access them using the index:


and you add elements using push:


When creating the array you can supply the initial values:

let arr1: boolean[] = [true, false];
let arr2: boolean[] = new Array(true, false);

How to remove folders with a certain name

Another one:

"-exec rm -rf {} \;" can be replaced by "-delete"

find -type d -name __pycache__ -delete      # GNU find
find . -type d -name __pycache__ -delete    # POSIX find (e.g. Mac OS X)

What does request.getParameter return?

String onevalue;   

What is a callback URL in relation to an API?

It's a mechanism to invoke an API in an asynchrounous way. The sequence is the following

  1. your app invokes the url, passing as parameter the callback url
  2. the api respond with a 20x http code (201 I guess, but refer to the api docs)
  3. the api works on your request for a certain amount of time
  4. the api invokes your app to give you the results, at the callback url address.

So you can invoke the api and tell your user the request is "processing" or "acquired" for example, and then update the status when you receive the response from the api.

Hope it makes sense. -G

How to turn IDENTITY_INSERT on and off using SQL Server 2008?

Import: You must write columns in INSERT statement


Is not correct.

Insert into Table(Field1,...)
Select (Field1,...) from TABLE

Is correct

Export data from R to Excel

writexl, without Java requirement:

# install.packages("writexl")
tempfile <- write_xlsx(iris)

Regarding Java switch statements - using return and omitting breaks in each case

I think that what you have written is perfectly fine. I also don't see any readability issue with having multiple return statements.

I would always prefer to return from the point in the code when I know to return and this will avoid running logic below the return.

There can be an argument for having a single return point for debugging and logging. But, in your code, there is no issue of debugging and logging if we use it. It is very simple and readable the way you wrote.

how to attach url link to an image?

"How to attach url link to an image?"

You do it like this:

<a href=""><img src=""/></a>

See it in action.

I didn't find "ZipFile" class in the "System.IO.Compression" namespace

For those who are green programmers in .NET, to add the DLL reference as MarcGravell noted, you follow these steps:

To add a reference in Visual C#

  1. In Solution Explorer, right-click the project node and click Add Reference.
  2. In the Add Reference dialog box, select the tab indicating the type of component you want to reference.
  3. Select the components you want to reference, and then click OK.

From the MSDN Article, How to: Add or Remove References By Using the Add Reference Dialog Box.

export html table to csv

Using just jQuery, vanilla Javascript, and the table2CSV library:


Put this code into a script to be loaded in the head section:

 $(document).ready(function () {
    $('table').each(function () {
        var $table = $(this);

        var $button = $("<button type='button'>");
        $button.text("Export to spreadsheet");

        $ () {
            var csv = $table.table2CSV({
                delivery: 'value'
            window.location.href = 'data:text/csv;charset=UTF-8,' 
            + encodeURIComponent(csv);


Requires jQuery and table2CSV: Add script references to both libraries before the script above.

The table selector is used as an example, and can be adjusted to suit your needs.

It only works in browsers with full Data URI support: Firefox, Chrome and Opera, not in IE, which only supports Data URIs for embedding binary image data into a page.

For full browser compatibility you would have to use a slightly different approach that requires a server side script to echo the CSV.

UL has margin on the left

The <ul> element has browser inherent padding & margin by default. In your case, Use

#footer ul {
    margin: 0; /* To remove default bottom margin */ 
    padding: 0; /* To remove default left padding */

or a CSS browser reset ( ) to deal with this.

How do I force Robocopy to overwrite files?

From the documentation:

/is Includes the same files. /it Includes "tweaked" files.

"Same files" means files that are identical (name, size, times, attributes). "Tweaked files" means files that have the same name, size, and times, but different attributes.

robocopy src dst sample.txt /is      # copy if attributes are equal
robocopy src dst sample.txt /it      # copy if attributes differ
robocopy src dst sample.txt /is /it  # copy irrespective of attributes

This answer on Super User has a good explanation of what kind of files the selection parameters match.

With that said, I could reproduce the behavior you describe, but from my understanding of the documentation and the output robocopy generated in my tests I would consider this a bug.

PS C:\temp> New-Item src -Type Directory >$null
PS C:\temp> New-Item dst -Type Directory >$null
PS C:\temp> New-Item src\sample.txt -Type File -Value "test001" >$null
PS C:\temp> New-Item dst\sample.txt -Type File -Value "test002" >$null
PS C:\temp> Set-ItemProperty src\sample.txt -Name LastWriteTime -Value "2016/1/1 15:00:00"
PS C:\temp> Set-ItemProperty dst\sample.txt -Name LastWriteTime -Value "2016/1/1 15:00:00"
PS C:\temp> robocopy src dst sample.txt /is /it /copyall /mir
  Options : /S /E /COPYALL /PURGE /MIR /IS /IT /R:1000000 /W:30


                           1    C:\temp\src\
            Modified                   7        sample.txt


               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         0         0         0         0
   Files :         1         1         0         0         0         0
   Bytes :         7         7         0         0         0         0
PS C:\temp> robocopy src dst sample.txt /is /it /copyall /mir
  Options : /S /E /COPYALL /PURGE /MIR /IS /IT /R:1000000 /W:30


                           1    C:\temp\src\
            Same                       7        sample.txt


               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         0         0         0         0
   Files :         1         1         0         0         0         0
   Bytes :         7         7         0         0         0         0
PS C:\temp> Get-Content .\src\sample.txt
PS C:\temp> Get-Content .\dst\sample.txt

The file is listed as copied, and since it becomes a same file after the first robocopy run at least the times are synced. However, even though seven bytes have been copied according to the output no data was actually written to the destination file in both cases despite the data flag being set (via /copyall). The behavior also doesn't change if the data flag is set explicitly (/copy:d).

I had to modify the last write time to get robocopy to actually synchronize the data.

PS C:\temp> Set-ItemProperty src\sample.txt -Name LastWriteTime -Value (Get-Date)
PS C:\temp> robocopy src dst sample.txt /is /it /copyall /mir
  Options : /S /E /COPYALL /PURGE /MIR /IS /IT /R:1000000 /W:30


                           1    C:\temp\src\
100%        Newer                      7        sample.txt


               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         0         0         0         0
   Files :         1         1         0         0         0         0
   Bytes :         7         7         0         0         0         0
PS C:\temp> Get-Content .\dst\sample.txt

An admittedly ugly workaround would be to change the last write time of same/tweaked files to force robocopy to copy the data:

& robocopy src dst /is /it /l /ndl /njh /njs /ns /nc |
  Where-Object { $_.Trim() } |
  ForEach-Object {
    $f = Get-Item $_
    $f.LastWriteTime = $f.LastWriteTime.AddSeconds(1)
& robocopy src dst /copyall /mir

Switching to xcopy is probably your best option:

& xcopy src dst /k/r/e/i/s/c/h/f/o/x/y

Binary Data in JSON String. Something better than Base64

I dig a little bit more (during implementation of base128), and expose that when we send characters which ascii codes are bigger than 128 then browser (chrome) in fact send TWO characters (bytes) instead one :(. The reason is that JSON by defaul use utf8 characters for which characters with ascii codes above 127 are coded by two bytes what was mention by chmike answer. I made test in this way: type in chrome url bar chrome://net-export/ , select "Include raw bytes", start capturing, send POST requests (using snippet at the bottom), stop capturing and save json file with raw requests data. Then we look inside that json file:

  • We can find our base64 request by finding string 4142434445464748494a4b4c4d4e this is hex coding of ABCDEFGHIJKLMN and we will see that "byte_count": 639 for it.
  • We can find our above127 request by finding string C2BCC2BDC380C381C382C383C384C385C386C387C388C389C38AC38B this are request-hex utf8 codes of characters ¼½ÀÁÂÃÄÅÆÇÈÉÊË (however the ascii hex codes of this characters are c1c2c3c4c5c6c7c8c9cacbcccdce). The "byte_count": 703 so it is 64bytes longer than base64 request because characters with ascii codes above 127 are code by 2 bytes in request :(

So in fact we don't have profit with sending characters with codes >127 :( . For base64 strings we not observe such negative behaviour (probably for base85 too - I don check it) - however may be some solution for this problem will be sending data in binary part of POST multipart/form-data described in Ælex answer (however usually in this case we don't need to use any base coding at all...).

The alternative approach may rely on mapping two bytes data portion into one valid utf8 character by code it using something like base65280 / base65k but probably it would be less effective than base64 due to utf8 specification ...

function postBase64() {_x000D_
  let formData = new FormData();_x000D_
  let req = new XMLHttpRequest();_x000D_
  formData.append("base64ch", "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");_x000D_"POST", '/testBase64ch');_x000D_
function postAbove127() {_x000D_
  let formData = new FormData();_x000D_
  let req = new XMLHttpRequest();_x000D_
  formData.append("above127", "¼½ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüý");_x000D_"POST", '/testAbove127');_x000D_
<button onclick=postBase64()>POST base64 chars</button>_x000D_
<button onclick=postAbove127()>POST chars with codes>127</button>

How can I get the number of records affected by a stored procedure?

For Microsoft SQL Server you can return the @@ROWCOUNT variable to return the number of rows affected by the last statement in the stored procedure.

MVC controller : get JSON object from HTTP body?

you can get the json string as a param of your ActionResult and afterwards serialize it using JSON.Net

HERE an example is being shown

in order to receive it in the serialized form as a param of the controller action you must either write a custom model binder or a Action filter (OnActionExecuting) so that the json string is serialized into the model of your liking and is available inside the controller body for use.

HERE is an implementation using the dynamic object

VBA collection: list of keys

You can easily iterate you collection. The example below is for the special Access TempVars collection, but works with any regular collection.

Dim tv As Long
For tv = 0 To TempVars.Count - 1
    Debug.Print TempVars(tv).Name, TempVars(tv).Value
Next tv

How to get number of video views with YouTube API?

Here an example that I used in my TubeCount app.

I also use the fields parameter to filter the JSON result, so only the fields that I need are returned.

var fields = "fields=openSearch:totalResults,entry(title,media:group(yt:videoid),media:group(yt:duration),media:group(media:description),media:group(media:thumbnail[@yt:name='default'](@url)),yt:statistics,yt:rating,published,gd:comments(gd:feedLink(@countHint)))";

var channel = "wiibart";

    url: ""+channel+"/uploads?"+fields+"&v=2&alt=json",
    success: function(data){

        var len = data.feed.entry.length;

        for(var k =0; k<len; k++){
            var yt = data.feed.entry[k];
            v.count = Number($statistics != undefined &&$statistics.viewCount != undefined ?$statistics.viewCount : 0);

Make a div into a link

This work for me:

<div onclick="location.href='page.html';"  style="cursor:pointer;">...</div>

Stretch and scale CSS background

Another great solution for this is Srobbin's Backstretch which can be applied to the body or any element on the page -

Why Maven uses JDK 1.6 but my java -version is 1.7

You can also do,


      <!-- maven-compiler-plugin , aka JAVA Compiler 1.7 -->


How to color System.out.println output?

I've written a library called AnsiScape that allows you to write coloured output in a more structured way:


AnsiScape ansiScape = new AnsiScape();
String colors = ansiScape.format("{red {blueBg Red text with blue background}} {b Bold text}");

The library it also allows you to define your own "escape classes" akin to css classes.


AnsiScapeContext context = new AnsiScapeContext();

// Defines a "class" for text
AnsiClass text = AnsiClass.withName("text").add(RED);
// Defines a "class" for the title used
AnsiClass title = AnsiClass.withName("title").add(BOLD, BLUE_BG, YELLOW);
// Defines a "class" to render urls
AnsiClass url = AnsiClass.withName("url").add(BLUE, UNDERLINE);

// Registering the classes to the context

// Creating an AnsiScape instance with the custom context
AnsiScape ansiScape = new AnsiScape(context);

String fmt = "{title Chapter 1}\n" +
              "{text So it begins:}\n" +
              "- {text Option 1}\n" +
              "- {text Url: {url}}";


How to implement authenticated routes in React Router 4?

I implemented using-

<Route path='/dashboard' render={() => (
    this.state.user.isLoggedIn ? 
    (<Dashboard authenticate={this.authenticate} user={this.state.user} />) : 
    (<Redirect to="/login" />)
)} />

authenticate props will be passed to components e.g. signup using which user state can be changed. Complete AppRoutes-

import React from 'react';
import { Switch, Route } from 'react-router-dom';
import { Redirect } from 'react-router';

import Home from '../pages/home';
import Login from '../pages/login';
import Signup from '../pages/signup';
import Dashboard from '../pages/dashboard';

import { config } from '../utils/Config';

export default class AppRoutes extends React.Component {

    constructor(props) {

        // initially assuming that user is logged out
        let user = {
            isLoggedIn: false

        // if user is logged in, his details can be found from local storage
        try {
            let userJsonString = localStorage.getItem(config.localStorageKey);
            if (userJsonString) {
                user = JSON.parse(userJsonString);
        } catch (exception) {

        // updating the state
        this.state = {
            user: user

        this.authenticate = this.authenticate.bind(this);

    // this function is called on login/logout
    authenticate(user) {
            user: user

        // updating user's details
        localStorage.setItem(config.localStorageKey, JSON.stringify(user));

    render() {
        return (
                <Route exact path='/' component={Home} />
                <Route exact path='/login' render={() => <Login authenticate={this.authenticate} />} />
                <Route exact path='/signup' render={() => <Signup authenticate={this.authenticate} />} />
                <Route path='/dashboard' render={() => (
                    this.state.user.isLoggedIn ? 
                            (<Dashboard authenticate={this.authenticate} user={this.state.user} />) : 
                            (<Redirect to="/login" />)
                )} />

Check the complete project here:

How do you redirect HTTPS to HTTP?

all the above did not work when i used cloudflare, this one worked for me:

RewriteCond %{HTTP:X-Forwarded-Proto} =https
RewriteRule ^(.*)$ http://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

and this one definitely works without proxies in the way:

RewriteCond %{HTTPS} on
RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

Getting net::ERR_UNKNOWN_URL_SCHEME while calling telephone number from HTML page in Android

I had this issue occurring with mailto: and tel: links inside an iframe (in Chrome, not a webview). Clicking the links would show the grey "page not found" page and inspecting the page showed it had a ERR_UNKNOWN_URL_SCHEME error.

Adding target="_blank", as suggested by this discussion of the issue fixed the problem for me.

Cannot change column used in a foreign key constraint

You can turn off foreign key checks:




Please make sure to NOT use this on production and have a backup.

Format Instant to String

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy MM dd");
String text = date.toString(formatter);
LocalDate date = LocalDate.parse(text, formatter);

I believe this might help, you may need to use some sort of localdate variation instead of instant

how to check if object already exists in a list

Another point to mention is that you should ensure that your equality function is as you expect. You should override the equals method to set up what properties of your object have to match for two instances to be considered equal.

Then you can just do mylist.contains(item)

Angular JS Uncaught Error: [$injector:modulerr]

The error means that the dependency injector was unable to locate the dependency 'ngResource'. The script tag in the accepted answer provides this dependency.

You will also get the same error if you add any custom modules in the dependencies but did not add the script tag for including the '.js' file containing the dependency.

Selecting multiple items in ListView

You have to select the option in ArrayAdapter:

ArrayAdapter<String> adapter = new ArrayAdapter<String>
    (this, android.R.layout.simple_list_item_single_choice, countries);

Communication between multiple docker-compose projects

For using another docker-compose network you just do these(to share networks between docker-compose):

  1. Run the first docker-compose project by up -d
  2. Find the network name of the first docker-compose by: docker network ls(It contains the name of the root directory project)
  3. Then use that name by this structure at below in the second docker-compose file.

second docker-compose.yml

version: '3'
  service-on-second-compose:  # Define any names that you want.
      - <put it here(the network name that comes from "docker network ls")>

  - <put it here(the network name that comes from "docker network ls")>:
    external: true

drag drop files into standard html file input

This is an improvement, bugfix, and modification of the example that William Entriken gave here. There were some issues with it. For example the normal button from <input type="file" /> didn't do anything (in case the user wanted to upload the file that way).

Notice: I am making a webapp that only I use, so this is only tested (and refined) for Firefox. I am sure though that this code is of value even if you develop for the crossbrowser situation.

function readFile(e) {
  var files;
  if ( {
  } else {
  if (files.length==0) {
    alert('What you dropped is not a file.');
  var file=files[0];
  document.getElementById('fileDragName').value =
  document.getElementById('fileDragSize').value = file.size
  document.getElementById('fileDragType').value = file.type
  reader = new FileReader();
  reader.onload = function(e) {
    document.getElementById('fileDragData').value =;
function getTheFile(e) {'#ccc';
<input type="file" onchange="readFile(event)">
<input id="fileDragName">
<input id="fileDragSize">
<input id="fileDragType">
<input id="fileDragData">
<div style="width:200px; height:200px; border: 10px dashed #ccc"
     ondragover="'#0c0';return false;"       
     ondrop="getTheFile(event); return false;"       

Creating a selector from a method name with parameters

SEL is a type that represents a selector in Objective-C. The @selector() keyword returns a SEL that you describe. It's not a function pointer and you can't pass it any objects or references of any kind. For each variable in the selector (method), you have to represent that in the call to @selector. For example:

SEL noParameterSelector = @selector(methodWithNoParameters);

SEL oneParameterSelector = @selector(methodWithOneParameter:); // notice the colon here

-(void)methodWIthTwoParameters:(id)parameterOne and:(id)parameterTwo;
SEL twoParameterSelector = @selector(methodWithTwoParameters:and:); // notice the parameter names are omitted

Selectors are generally passed to delegate methods and to callbacks to specify which method should be called on a specific object during a callback. For instance, when you create a timer, the callback method is specifically defined as:


So when you schedule the timer you would use @selector to specify which method on your object will actually be responsible for the callback:

@implementation MyObject

    // do some computations
    if( timerShouldEnd ) {
      [timer invalidate];


// ...

int main(int argc, const char **argv)
    // do setup stuff
    MyObject* obj = [[MyObject alloc] init];
    SEL mySelector = @selector(myTimerCallback:);
    [NSTimer scheduledTimerWithTimeInterval:30.0 target:obj selector:mySelector userInfo:nil repeats:YES];
    // do some tear-down
    return 0;

In this case you are specifying that the object obj be messaged with myTimerCallback every 30 seconds.

Can't find out where does a node.js app running and can't kill it

I use fkill


npm i fkill-cli -g


Search process in command line


OR: kill ! ALL process

fkill node

OR: kill process using port 8080

fkill :8080

Class vs. static method in JavaScript

There are tree ways methods and properties are implemented on function or class objects, and on they instances.

  1. On the class (or function) itself : Foo.method() or Foo.prop. Those are static methods or properties
  2. On its prototype : Foo.prototype.method() or Foo.prototype.prop. When created, the instances will inherit those object via the prototype witch is {method:function(){...}, prop:...}. So the foo object will receive, as prototype, a copy of the Foo.prototype object.
  3. On the instance itself : the method or property is added to the object itself. foo={method:function(){...}, prop:...}

The this keyword will represent and act differently according to the context. In a static method, it will represent the class itself (witch is after all an instance of Function : class Foo {} is quite equivalent to let Foo = new Function({})

With ECMAScript 2015, that seems well implemented today, it is clearer to see the difference between class (static) methods and properties, instance methods and properties and own methods ans properties. You can thus create three method or properties having the same name, but being different because they apply to different objects, the this keyword, in methods, will apply to, respectively, the class object itself and the instance object, by the prototype or by its own.

class Foo {
  static prop = "I am static" // see 1.
  static method(str) {alert("static method"+str+" :"+this.prop)} // see 1.
  prop="I am of an instance"; // see 2.
  method(str) {alert("instance method"+str+" : "+this.prop)} // see 2.

var foo= new Foo();
foo.prop = "I am of own";  // see 3.
foo.func = function(str){alert("own method" + str + this.prop)} // see 3.

TypeError: a bytes-like object is required, not 'str' when writing to a file in Python3

Use encode() function along with hardcoded String value given in a single quote.


file.write(answers[i] + '\n'.encode())


line.split(' +++$+++ '.encode())

How do I use InputFilter to limit characters in an EditText in Android?

It is possible to use setOnKeyListener. In this method, we can customize the input edittext !

How to read an entire file to a string using C#?

string content = System.IO.File.ReadAllText( @"C:\file.txt" );

Configuring ObjectMapper in Spring

I am using Spring 3.2.4 and Jackson FasterXML 2.1.1.

I have created a custom JacksonObjectMapper that works with explicit annotations for each attribute of the Objects mapped:

package com.test;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class MyJaxbJacksonObjectMapper extends ObjectMapper {

public MyJaxbJacksonObjectMapper() {

    this.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY)
            .setVisibility(PropertyAccessor.CREATOR, JsonAutoDetect.Visibility.ANY)
            .setVisibility(PropertyAccessor.SETTER, JsonAutoDetect.Visibility.NONE)
            .setVisibility(PropertyAccessor.GETTER, JsonAutoDetect.Visibility.NONE)
            .setVisibility(PropertyAccessor.IS_GETTER, JsonAutoDetect.Visibility.NONE);

    this.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

Then this is instantiated in the context-configuration (servlet-context.xml):


        <beans:bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
            <beans:property name="objectMapper">
                <beans:bean class="com.test.MyJaxbJacksonObjectMapper" />


This works fine!

How to compare 2 files fast using .NET?

If the files are not too big, you can use:

public static byte[] ComputeFileHash(string fileName)
    using (var stream = File.OpenRead(fileName))
        return System.Security.Cryptography.MD5.Create().ComputeHash(stream);

It will only be feasible to compare hashes if the hashes are useful to store.

(Edited the code to something much cleaner.)

[Vue warn]: Cannot find element

I think the problem is your script is executed before the target dom element is loaded in the dom... one reason could be that you have placed your script in the head of the page or in a script tag that is placed before the div element #main. So when the script is executed it won't be able to find the target element thus the error.

One solution is to place your script in the load event handler like

window.onload = function () {
    var main = new Vue({
        el: '#main',
        data: {
            currentActivity: 'home'

Another syntax

window.addEventListener('load', function () {
    //your script

removing table border

.yourClass>tbody>tr>td{border: 1px solid #ffffff !important;}

How do you force a CIFS connection to unmount

umount -f -t cifs -l /mnt &

Be careful of &, let umount run in background. umount will detach filesystem first, so you will find nothing abount /mnt. If you run df command, then it will umount /mnt forcibly.

Difference between add(), replace(), and addToBackStack()

Although it is an old question already answered, maybe those next examples can complement the accepted answer and they can be useful for some new programmers in Android as I am.

Option 1 - "addToBackStack()" is never used

Case 1A - adding, removing, and clicking Back button

Activity :      onCreate() - onStart() - onResume()                             Activity is visible
add Fragment A :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment A is visible
add Fragment B :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment B is visible
add Fragment C :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment C is visible
remove Fragment C :     onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Fragment B is visible
(Back button clicked)
Activity :      onPause() - onStop() - onDestroy()
Fragment A :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()
Fragment B :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               App is closed, nothing is visible

Case 1B - adding, replacing, and clicking Back button

Activity :      onCreate() - onStart() - onResume()                             Activity is visible
add Fragment A :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment A is visible
add Fragment B :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment B is visible
(replace Fragment C)    
Fragment B :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               
Fragment A :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()
Fragment C :        onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment C is visible
(Back button clicked)
Activity :      onPause() - onStop() - onDestroy()
Fragment C :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               App is closed, nothing is visible

Option 2 - "addToBackStack()" is always used

Case 2A - adding, removing, and clicking Back button

Activity :      onCreate() - onStart() - onResume()                             Activity is visible
add Fragment A :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment A is visible
add Fragment B :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment B is visible
add Fragment C :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment C is visible
remove Fragment C :     onPause() - onStop() - onDestroyView()                              Fragment B is visible
(Back button clicked)
Fragment C :        onCreateView() - onActivityCreated() - onStart() - onResume()                   Fragment C is visible
(Back button clicked)
Fragment C :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Fragment B is visible
(Back button clicked)
Fragment B :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Fragment A is visible
(Back button clicked)
Fragment A :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Activity is visible
(Back button clicked)
Activity :      onPause() - onStop() - onDestroy()                              App is closed, nothing is visible

Case 2B - adding, replacing, removing, and clicking Back button

Activity :      onCreate() - onStart() - onResume()                             Activity is visible
add Fragment A :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment A is visible
add Fragment B :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment B is visible
(replace Fragment C)    
Fragment B :        onPause() - onStop() - onDestroyView()  
Fragment A :        onPause() - onStop() - onDestroyView() 
Fragment C :        onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment C is visible
remove Fragment C :     onPause() - onStop() - onDestroyView()                              Activity is visible
(Back button clicked)
Fragment C :        onCreateView() - onActivityCreated() - onStart() - onResume()                   Fragment C is visible
(Back button clicked)
Fragment C :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               
Fragment A :        onCreateView() - onActivityCreated() - onStart() - onResume()   
Fragment B :        onCreateView() - onActivityCreated() - onStart() - onResume()                   Fragment B is visible
(Back button clicked)
Fragment B :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Fragment A is visible
(Back button clicked)
Fragment A :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Activity is visible
(Back button clicked)
Activity :      onPause() - onStop() - onDestroy()                              App is closed, nothing is visible

Option 3 - "addToBackStack()" is not used always (in the below examples, w/o indicates that it is not used)

Case 3A - adding, removing, and clicking Back button

Activity :      onCreate() - onStart() - onResume()                             Activity is visible
add Fragment A :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment A is visible
add Fragment B w/o:     onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment B is visible
add Fragment C w/o:     onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment C is visible
remove Fragment C :     onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Fragment B is visible
(Back button clicked)
Fragment B :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               
Fragment A :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Activity is visible
(Back button clicked)
Activity :      onPause() - onStop() - onDestroy()                              App is closed, nothing is visible

Case 3B - adding, replacing, removing, and clicking Back button

Activity :      onCreate() - onStart() - onResume()                             Activity is visible
add Fragment A :    onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment A is visible
add Fragment B w/o:     onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment B is visible
(replace Fragment C)    
Fragment B :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()   
Fragment A :        onPause() - onStop() - onDestroyView() 
Fragment C :        onAttach() - onCreate() - onCreateView() - onActivityCreated() - onStart() - onResume()     Fragment C is visible
remove Fragment C :     onPause() - onStop() - onDestroyView()                              Activity is visible
(Back button clicked)
Fragment C :        onCreateView() - onActivityCreated() - onStart() - onResume()                   Fragment C is visible
(Back button clicked)
Fragment C :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               
Fragment A :        onCreateView() - onActivityCreated() - onStart() - onResume()                   Fragment A is visible
(Back button clicked)
Fragment A :        onPause() - onStop() - onDestroyView() - onDestroy() - onDetach()               Activity is visible
(Back button clicked)
Activity :      onPause() - onStop() - onDestroy()                              App is closed, nothing is visible

Could not instantiate mail function. Why this error occurring

To revisit an old thread, my issue was that one of the "AddressTo" email addresses was not valid. Removing that email address removed the error.

How to specify Memory & CPU limit in docker compose version 3

Docker Compose does not support the deploy key. It's only respected when you use your version 3 YAML file in a Docker Stack.

This message is printed when you add the deploy key to you docker-compose.yml file and then run docker-compose up -d

WARNING: Some services (database) use the 'deploy' key, which will be ignored. Compose does not support 'deploy' configuration - use docker stack deploy to deploy to a swarm.

The documentation ( says:

Specify configuration related to the deployment and running of services. This only takes effect when deploying to a swarm with docker stack deploy, and is ignored by docker-compose up and docker-compose run.

Sending a JSON HTTP POST request from Android

try some thing like blow:

SString otherParametersUrServiceNeed =  "Company=acompany&Lng=test&MainPeriod=test&UserID=123&CourseDate=8:10:10";
String request = "";

URL url = new URL(request); 
HttpURLConnection connection = (HttpURLConnection) url.openConnection();   
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); 
connection.setRequestProperty("charset", "utf-8");
connection.setRequestProperty("Content-Length", "" + Integer.toString(otherParametersUrServiceNeed.getBytes().length));
connection.setUseCaches (false);

DataOutputStream wr = new DataOutputStream(connection.getOutputStream ());

   JSONObject jsonParam = new JSONObject();
jsonParam.put("ID", "25");
jsonParam.put("description", "Real");
jsonParam.put("enable", "true");



References :

  2. Java - sending HTTP parameters via POST method easily

Ubuntu: Using curl to download an image

For ones who got permission denied for saving operation, here is the command that worked for me:

$ curl --output py.png

onKeyPress Vs. onKeyUp and onKeyDown

This article by Jan Wolter is the best piece I have came across, you can find the archived copy here if link is dead.

It explains all browser key events really well,

The keydown event occurs when the key is pressed, followed immediately by the keypress event. Then the keyup event is generated when the key is released.

To understand the difference between keydown and keypress, it is useful to distinguish between characters and keys. A key is a physical button on the computer's keyboard. A character is a symbol typed by pressing a button. On a US keyboard, hitting the 4 key while holding down the Shift key typically produces a "dollar sign" character. This is not necessarily the case on every keyboard in the world. In theory, the keydown and keyup events represent keys being pressed or released, while the keypress event represents a character being typed. In practice, this is not always the way it is implemented.

For a while, some browers fired an additional event, called textInput, immediately after keypress. Early versions of the DOM 3 standard intended this as a replacement for the keypress event, but the whole notion was later revoked. Webkit supported this between versions 525 and 533, and I'm told IE supported it, but I never detected that, possibly because Webkit required it to be called textInput while IE called it textinput.

There is also an event called input, supported by all browsers, which is fired just after a change is made to to a textarea or input field. Typically keypress will fire, then the typed character will appear in the text area, then input will fire. The input event doesn't actually give any information about what key was typed - you'd have to inspect the textbox to figure it out what changed - so we don't really consider it a key event and don't really document it here. Though it was originally defined only for textareas and input boxes, I believe there is some movement toward generalizing it to fire on other types of objects as well.

How do I create an iCal-type .ics file that can be downloaded by other users?

That will work just fine. You can export an entire calendar with File > Export…, or individual events by dragging them to the Finder.

iCalendar (.ics) files are human-readable, so you can always pop it open in a text editor to make sure no private events made it in there. They consist of nested sections with start with BEGIN: and end with END:. You'll mostly find VEVENT sections (each of which represents an event) and VTIMEZONE sections, each of which represents a time zone that's referenced from one or more events.

How to return an array from an AJAX call?

Php has a super sexy function for this, just pass the array to it:

$json = json_encode($var);

dataType : "json",

simples :)

Detect click outside Angular component

ginalx's answer should be set as the default one imo: this method allows for many optimizations.

The problem

Say that we have a list of items and on every item we want to include a menu that needs to be toggled. We include a toggle on a button that listens for a click event on itself (click)="toggle()", but we also want to toggle the menu whenever the user clicks outside of it. If the list of items grows and we attach a @HostListener('document:click') on every menu, then every menu loaded within the item will start listening for the click on the entire document, even when the menu is toggled off. Besides the obvious performance issues, this is unnecessary.

You can, for example, subscribe whenever the popup gets toggled via a click and start listening for "outside clicks" only then.

isActive: boolean = false;

// to prevent memory leaks and improve efficiency, the menu
// gets loaded only when the toggle gets clicked
private _toggleMenuSubject$: BehaviorSubject<boolean>;
private _toggleMenu$: Observable<boolean>;

private _toggleMenuSub: Subscription;
private _clickSub: Subscription = null;

 private _utilitiesService: UtilitiesService,
 private _elementRef: ElementRef,
 this._toggleMenuSubject$ = new BehaviorSubject(false);
 this._toggleMenu$ = this._toggleMenuSubject$.asObservable();


ngOnInit() {
 this._toggleMenuSub = this._toggleMenu$.pipe(
      tap(isActive => {
        logger.debug('Label Menu is active', isActive)
        this.isActive = isActive;

        // subscribe to the click event only if the menu is Active
        // otherwise unsubscribe and save memory
        if(isActive === true){
          this._clickSub = this._utilitiesService.documentClickedTarget
           .subscribe(target => this._documentClickListener(target));
        }else if(isActive === false && this._clickSub !== null){

      // other observable logic

toggle() {

private _documentClickListener(targetElement: HTMLElement): void {
    const clickedInside = this._elementRef.nativeElement.contains(targetElement);
    if (!clickedInside) {


And, in *.component.html:

<button (click)="toggle()">Toggle the menu</button>

Classes residing in App_Code is not accessible

Put this at the top of the other files where you want to access the class:

using CLIck10.App_Code;

OR access the class from other files like this:


Not sure if that's your issue or not but if you were new to C# then this is an easy one to get tripped up on.

Update: I recently found that if I add an App_Code folder to a project, then I must close/reopen Visual Studio for it to properly recognize this "special" folder. main method

One more way is to extend the application (as my application was to inherit and customize the parent). It invokes the parent and its commandlinerunner automatically.

public class ChildApplication extends ParentApplication{
    public static void main(String[] args) {, args);

How can an html element fill out 100% of the remaining screen height, using css only?

The trick to this is specifying 100% height on the html and body elements. Some browsers look to the parent elements (html, body) to calculate the height.

        <div id="Header">
        <div id="Content">

html, body
    height: 100%;
    width: 960px;
    height: 150px;
    height: 100%;
    width: 960px;

How to extract numbers from a string and get an array of ints?

public static String extractNumberFromString(String number) {
    String num = number.replaceAll("[^0-9]+", " ");
    return num.replaceAll(" ", "");

extracts only numbers from string

How can I install packages using pip according to the requirements.txt file from a local directory?

This works for everyone:

pip install -r /path/to/requirements.txt

Passing just a type as a parameter in C#

You can do this, just wrap it in typeof()


public void GetColumnValues(Type type)

How can I check if a checkbox is checked?

use like this

<script type=text/javascript>
function validate(){
if (document.getElementById('remember').checked){
          alert("checked") ;
alert("You didn't check it! Let me check it for you.")

<input id="remember" name="remember" type="checkbox" onclick="validate()" />

Why can't I use background image and color together?

background:url(directoryName/imageName.extention) bottom left no-repeat; 
background-color: red;

MySQL parameterized queries

You have a few options available. You'll want to get comfortable with python's string iterpolation. Which is a term you might have more success searching for in the future when you want to know stuff like this.

Better for queries:

some_dictionary_with_the_data = {
    'name': 'awesome song',
    'artist': 'some band',
cursor.execute ("""
            INSERT INTO Songs (SongName, SongArtist, SongAlbum, SongGenre, SongLength, SongLocation)
                (%(name)s, %(artist)s, %(album)s, %(genre)s, %(length)s, %(location)s)

        """, some_dictionary_with_the_data)

Considering you probably have all of your data in an object or dictionary already, the second format will suit you better. Also it sucks to have to count "%s" appearances in a string when you have to come back and update this method in a year :)

Check whether a path is valid

private bool IsValidPath(string path)
    Regex driveCheck = new Regex(@"^[a-zA-Z]:\\$");

    if (string.IsNullOrWhiteSpace(path) || path.Length < 3)
        return false;

    if (!driveCheck.IsMatch(path.Substring(0, 3)))
        return false;

    var x1 = (path.Substring(3, path.Length - 3));
    string strTheseAreInvalidFileNameChars = new string(Path.GetInvalidPathChars());
    strTheseAreInvalidFileNameChars += @":?*";
    Regex containsABadCharacter = new Regex("[" + Regex.Escape(strTheseAreInvalidFileNameChars) + "]");

    if (containsABadCharacter.IsMatch(path.Substring(3, path.Length - 3)))
        return false;

    var driveLetterWithColonAndSlash = Path.GetPathRoot(path);

    if (!DriveInfo.GetDrives().Any(x => x.Name == driveLetterWithColonAndSlash))
        return false;

    return true;

Convert List<Object> to String[] in Java

There is a simple way available in Kotlin

var lst: List<Object> = ...
listOFStrings: ArrayList<String> = (lst!!.map { })

How do I update a Linq to SQL dbml file?

There are three ways to keep the model in sync.

  1. Delete the modified tables from the designer, and drag them back onto the designer surface from the Database Explorer. I have found that, for this to work reliably, you have to:

    a. Refresh the database schema in the Database Explorer (right-click, refresh)
    b. Save the designer after deleting the tables
    c. Save again after dragging the tables back.

    Note though that if you have modified any properties (for instance, turning off the child property of an association), this will obviously lose those modifications — you'll have to make them again.

  2. Use SQLMetal to regenerate the schema from your database. I have seen a number of blog posts that show how to script this.

  3. Make changes directly in the Properties pane of the DBML. This works for simple changes, like allowing nulls on a field.

The DBML designer is not installed by default in Visual Studio 2015, 2017 or 2019. You will have to close VS, start the VS installer and modify your installation. The LINQ to SQL tools is the feature you must install. For VS 2017/2019, you can find it under Individual Components > Code Tools.

Is this how you define a function in jQuery?

First of all, your code works and that's a valid way of creating a function in JavaScript (jQuery aside), but because you are declaring a function inside another function (an anonymous one in this case) "MyBlah" will not be accessible from the global scope.

Here's an example:

$(document).ready( function () {

    var MyBlah = function($blah) { alert($blah);  };

    MyBlah("Hello this works") // Inside the anonymous function we are cool.


MyBlah("Oops") //This throws a JavaScript error (MyBlah is not a function)

This is (sometimes) a desirable behavior since we do not pollute the global namespace, so if your function does not need to be called from other part of your code, this is the way to go.

Declaring it outside the anonymous function places it in the global namespace, and it's accessible from everywhere.

Lastly, the $ at the beginning of the variable name is not needed, and sometimes used as a jQuery convention when the variable is an instance of the jQuery object itself (not necessarily in this case).

Maybe what you need is creating a jQuery plugin, this is very very easy and useful as well since it will allow you to do something like this:


See also:

filedialog, tkinter and opening files

I had to specify individual commands first and then use the * to bring all in command.

from tkinter import filedialog
from tkinter import *

How to list files inside a folder with SQL Server

You can use xp_dirtree

It takes three parameters:

Path of a Root Directory, Depth up to which you want to get files and folders and the last one is for showing folders only or both folders and files.

EXAMPLE: EXEC xp_dirtree 'C:\', 2, 1

How do I run a docker instance from a DockerFile?

Straightforward and easy solution is:

docker build .
=> ....
=> Successfully built a3e628814c67
docker run -p 3000:3000 a3e628814c67

3000 - can be any port

a3e628814c68 - hash result given by success build command

NOTE: you should be within directory that contains Dockerfile.

How do I parse a URL query parameters, in Javascript?

You could get a JavaScript object containing the parameters with something like this:

var regex = /[?&]([^=#]+)=([^&#]*)/g,
    url = window.location.href,
    params = {},
while(match = regex.exec(url)) {
    params[match[1]] = match[2];

The regular expression could quite likely be improved. It simply looks for name-value pairs, separated by = characters, and pairs themselves separated by & characters (or an = character for the first one). For your example, the above would result in:

{v: "123", p: "hello"}

Here's a working example.

The content type application/xml;charset=utf-8 of the response message does not match the content type of the binding (text/xml; charset=utf-8)

This could be an error in the web.config file.

Open up your URL in your browser, example:


Check if you have a 500 Error.

HTTP Error 500.19 - Internal Server Error

Look for the error in these sections:

Config Error

Config File

How to set the focus for a particular field in a Bootstrap modal, once it appears

I've created a dynamic way to call each event automatically. It perfect to focus a field, because it call the event just once, removing it after use.

function modalEvents() {
    var modal = $('#modal');
    var events = ['show', 'shown', 'hide', 'hidden'];

    $(events).each(function (index, event) {
        modal.on(event + '.bs.modal', function (e) {
            var callback = + '-callback');
            if (typeof callback != 'undefined') {
                modal.removeData(event + '-callback');

You just need to call modalEvents() on document ready.


$('#modal').data('show-callback', function() {

So, you can use the same modal to load what you want without worry about remove events every time.

Make .gitignore ignore everything except a few files

If you want to ignore the whole content of a directory except one file inside it, you could write a pair of rules for each directory in the file path. E.g. .gitignore to ignore the pippo folder except from pippo/pluto/paperino.xml


Note that if you simply had written above:


It wouldn't work because the intermediary pluto folder would not exist to Git, so paperino.xml could not find a place in which to exist.

How to parse a JSON string into JsonNode in Jackson?

A third variant:

ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readValue("{\"k1\":\"v1\"}", JsonNode.class);

What's the difference between "&nbsp;" and " "?

When having line-breaks, the line will not break when you use an $bnsp; because it's a 'non-breaking space'. This can be important if you have certain product-names or such, that always shall be written together.

Can be interesting if you (have to) use a whitespace as delimiter in numbers, like 12344567, that is displayed 12 344 567 in France. Without the   the line would break in the middle of the number, very ugly. Test:12 344 567

How to run VBScript from command line without Cscript/Wscript

You may follow the following steps:

  • Open your CMD(Command Prompt)
  • Type 'D:' and hit Enter. Example: C:\Users\[Your User Name]>D:
  • Type 'CD VBS' and hit Enter. Example: D:>CD VBS
  • Type 'Converter.vbs' or 'start Converter.vbs' and hit Enter. Example: D:\VBS>Converter.vbs Or D:\VBS>start Converter.vbs

Laravel 5.1 API Enable Cors

For me i put this codes in public\index.php file. and it worked just fine for all CRUD operations.

header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: GET, PUT, POST, DELETE, OPTIONS, post, get');
header("Access-Control-Max-Age", "3600");
header('Access-Control-Allow-Headers: Origin, Content-Type, X-Auth-Token');
header("Access-Control-Allow-Credentials", "true");

CSS container div not getting height

Add the following property:

    overflow: hidden;

This will force the container to respect the height of all elements within it, regardless of floating elements.


Recently, I was working on a project that required this trick, but needed to allow overflow to show, so instead, you can use a pseudo-element to clear your floats, effectively achieving the same effect while allowing overflow on all elements.

    clear: both;
    content: "";
    display: block;

Apache Tomcat Not Showing in Eclipse Server Runtime Environments

Scenario 1: You had Eclipse showing server and now after removing the particular version you want to configure at Eclipse a new local server instance. But you can not move further.

This happens due to reason Eclipse still looks for configured version of Tomcat directory, which directory is no longer there.

There is no need till LUNA to make fresh installation!

All we need is to REPLACE the new server run time environment into eclipse after removing old one, which is non-existent. Eclipse will

enter image description here

Android - SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length

Try using the default Android keyboard it will disappear

How to unzip a list of tuples into individual lists?

If you want a list of lists:

>>> [list(t) for t in zip(*l)]
[[1, 3, 8], [2, 4, 9]]

If a list of tuples is OK:

>>> zip(*l)
[(1, 3, 8), (2, 4, 9)]

How to push elements in JSON from javascript array

var arr = [ 'a', 'b', 'c'];
arr.push('d'); // insert as last item

Find which commit is currently checked out in Git

You can just do:

git rev-parse HEAD

To explain a bit further: git rev-parse is git's basic command for interpreting any of the exotic ways that you can specify the name of a commit and HEAD is a reference to your current commit or branch. (In a git bisect session, it points directly to a commit ("detached HEAD") rather than a branch.)

Alternatively (and easier to remember) would be to just do:

git show

... which defaults to showing the commit that HEAD points to. For a more concise version, you can do:

$ git show --oneline -s
c0235b7 Autorotate uploaded images based on EXIF orientation

Why use prefixes on member variables in C++ classes

You should never need such a prefix. If such a prefix offers you any advantage, your coding style in general needs fixing, and it's not the prefix that's keeping your code from being clear. Typical bad variable names include "other" or "2". You do not fix that with requiring it to be mOther, you fix it by getting the developer to think about what that variable is doing there in the context of that function. Perhaps he meant remoteSide, or newValue, or secondTestListener or something in that scope.

It's an effective anachronism that's still propagated too far. Stop prefixing your variables and give them proper names whose clarity reflects how long they're used. Up to 5 lines you could call it "i" without confusion; beyond 50 lines you need a pretty long name.

Determine function name from within that function (without using traceback)

There are a few ways to get the same result:

from __future__ import print_function
import sys
import inspect

def what_is_my_name():

Note that the inspect.stack calls are thousands of times slower than the alternatives:

$ python -m timeit -s 'import inspect, sys' 'inspect.stack()[0][0].f_code.co_name'
1000 loops, best of 3: 499 usec per loop
$ python -m timeit -s 'import inspect, sys' 'inspect.stack()[0][3]'
1000 loops, best of 3: 497 usec per loop
$ python -m timeit -s 'import inspect, sys' 'inspect.currentframe().f_code.co_name'
10000000 loops, best of 3: 0.1 usec per loop
$ python -m timeit -s 'import inspect, sys' 'sys._getframe().f_code.co_name'
10000000 loops, best of 3: 0.135 usec per loop

Replace non ASCII character from string

CharMatcher.retainFrom can be used, if you're using the Google Guava library:

String s = "A função";
String stripped = CharMatcher.ascii().retainFrom(s);
System.out.println(stripped); // Prints "A funo"

Ruby String to Date Conversion

Date.strptime(updated,"%a, %d %m %Y %H:%M:%S %Z")

Should be:

Date.strptime(updated, '%a, %d %b %Y %H:%M:%S %Z')

How do I check whether an array contains a string in TypeScript?

If your code is ES7 based (or upper versions):

channelArray.includes('three'); //will return true or false

If not, for example you are using IE with no babel transpile:

channelArray.indexOf('three') !== -1; //will return true or false

the indexOf method will return the position the element has into the array, because of that we use !== different from -1 if the needle is found at the first position.

How can I produce an effect similar to the iOS 7 blur view?

Why bother replicating the effect? Just draw a UIToolbar behind your view.

myView.backgroundColor = [UIColor clearColor];
UIToolbar* bgToolbar = [[UIToolbar alloc] initWithFrame:myView.frame];
bgToolbar.barStyle = UIBarStyleDefault;
[myView.superview insertSubview:bgToolbar belowSubview:myView];

Copying a HashMap in Java

If we want to copy an object in Java, there are two possibilities that we need to consider: a shallow copy and a deep copy.

The shallow copy is the approach when we only copy field values. Therefore, the copy might be dependent on the original object. In the deep copy approach, we make sure that all the objects in the tree are deeply copied, so the copy is not dependent on any earlier existing object that might ever change.

This question is the perfect definition for the application of the deep copy approach.

First, if you have a simple HashMap<Integer, List<T>> map then we just create a workaround like this. Creating a new instance of the List<T>.

public static <T> HashMap<Integer, List<T>> deepCopyWorkAround(HashMap<Integer, List<T>> original)
    HashMap<Integer, List<T>> copy = new HashMap<>();
    for (Map.Entry<Integer, List<T>> entry : original.entrySet()) {
        copy.put(entry.getKey(), new ArrayList<>(entry.getValue()));
    return copy;

This one uses Stream.collect() method to create the clone map, but uses the same idea as the previous method.

public static <T> Map<Integer, List<T>> deepCopyStreamWorkAround(Map<Integer, List<T>> original)
    return original
            .collect(Collectors.toMap(Map.Entry::getKey, valueMapper -> new ArrayList<>(valueMapper.getValue())));

But, if the instances inside T are also mutable objects we have a big problem. In this case a real deep copy is an alternative that solves this problem. Its advantage is that at least each mutable object in the object graph is recursively copied. Since the copy is not dependent on any mutable object that was created earlier, it won’t get modified by accident like we saw with the shallow copy.

To solve that this deep copy implementations will do the work.

public class DeepClone
    public static void main(String[] args)
        Map<Long, Item> itemMap = Stream.of(
                entry(0L, new Item(2558584)),
                entry(1L, new Item(254243232)),
                entry(2L, new Item(986786)),
                entry(3L, new Item(672542)),
                entry(4L, new Item(4846)),
                entry(5L, new Item(76867467)),
                entry(6L, new Item(986786)),
                entry(7L, new Item(7969768)),
                entry(8L, new Item(68868486)),
                entry(9L, new Item(923)),
                entry(10L, new Item(986786)),
                entry(11L, new Item(549768)),
                entry(12L, new Item(796168)),
                entry(13L, new Item(868421)),
                entry(14L, new Item(923)),
                entry(15L, new Item(986786)),
                entry(16L, new Item(549768)),
                entry(17L, new Item(4846)),
                entry(18L, new Item(4846)),
                entry(19L, new Item(76867467)),
                entry(20L, new Item(986786)),
                entry(21L, new Item(7969768)),
                entry(22L, new Item(923)),
                entry(23L, new Item(4846)),
                entry(24L, new Item(986786)),
                entry(25L, new Item(549768))

        Map<Long, Item> clone = DeepClone.deepClone(itemMap);


    private DeepClone() {}

    public static <T> T deepClone(final T input)
        if (input == null) return null;

        if (input instanceof Map<?, ?>) {
            return (T) deepCloneMap((Map<?, ?>) input);
        } else if (input instanceof Collection<?>) {
            return (T) deepCloneCollection((Collection<?>) input);
        } else if (input instanceof Object[]) {
            return (T) deepCloneObjectArray((Object[]) input);
        } else if (input.getClass().isArray()) {
            return (T) clonePrimitiveArray((Object) input);

        return input;

    private static Object clonePrimitiveArray(final Object input)
        final int length = Array.getLength(input);
        final Object output = Array.newInstance(input.getClass().getComponentType(), length);
        System.arraycopy(input, 0, output, 0, length);
        return output;

    private static <E> E[] deepCloneObjectArray(final E[] input)
        final E[] clone = (E[]) Array.newInstance(input.getClass().getComponentType(), input.length);
        for (int i = 0; i < input.length; i++) {
            clone[i] = deepClone(input[i]);

        return clone;

    private static <E> Collection<E> deepCloneCollection(final Collection<E> input)
        Collection<E> clone;
        if (input instanceof LinkedList<?>) {
            clone = new LinkedList<>();
        } else if (input instanceof SortedSet<?>) {
            clone = new TreeSet<>();
        } else if (input instanceof Set) {
            clone = new HashSet<>();
        } else {
            clone = new ArrayList<>();

        for (E item : input) {

        return clone;

    private static <K, V> Map<K, V> deepCloneMap(final Map<K, V> map)
        Map<K, V> clone;
        if (map instanceof LinkedHashMap<?, ?>) {
            clone = new LinkedHashMap<>();
        } else if (map instanceof TreeMap<?, ?>) {
            clone = new TreeMap<>();
        } else {
            clone = new HashMap<>();

        for (Map.Entry<K, V> entry : map.entrySet()) {
            clone.put(deepClone(entry.getKey()), deepClone(entry.getValue()));

        return clone;

selectOneMenu ajax events

Be carefull that the page does not contain any empty component which has "required" attribute as "true" before your selectOneMenu component running.
If you use a component such as

<p:inputText label="Nm:" id="id_name" value="#{}" required="true"/>


<p:selectOneMenu .....></p:selectOneMenu>

and forget to fill the required component, ajax listener of selectoneMenu cannot be executed.

Create an Android GPS tracking application

Basically you need following things to make location detector android app

Now if you write each of these module yourself then it needs much time and efforts. So it would be better to use ready resources that are being maintained already.

Using all these resources, you will be able to create an flawless android location detection app.

1. Location Listening

You will first need to listen for current location of user. You can use any of below libraries to quick start.

Google Play Location Samples

This library provide last known location, location updates

Location Manager

With this library you just need to provide a Configuration object with your requirements, and you will receive a location or a fail reason with all the stuff are described above handled.

Live Location Sharing

Use this open source repo of the Hypertrack Live app to build live location sharing experience within your app within a few hours. HyperTrack Live app helps you share your Live Location with friends and family through your favorite messaging app when you are on the way to meet up. HyperTrack Live uses HyperTrack APIs and SDKs.

2. Markers Library

Google Maps Android API utility library

  • Marker clustering — handles the display of a large number of points
  • Heat maps — display a large number of points as a heat map
  • IconGenerator — display text on your Markers
  • Poly decoding and encoding — compact encoding for paths, interoperability with Maps API web services
  • Spherical geometry — for example: computeDistance, computeHeading, computeArea
  • KML — displays KML data
  • GeoJSON — displays and styles GeoJSON data

3. Polyline Libraries


If you want to add route maps feature in your apps you can use DrawRouteMaps to make you work more easier. This is lib will help you to draw route maps between two point LatLng.


Simple, smooth animation for route / polylines on google maps using projections. (WIP)


This project allows you to calculate the direction between two locations and display the route on a Google Map using the Google Directions API.

A map demo app for quick start with maps

Create file path from variables

You want the path.join() function from os.path.

>>> from os import path
>>> path.join('foo', 'bar')

This builds your path with os.sep (instead of the less portable '/') and does it more efficiently (in general) than using +.

However, this won't actually create the path. For that, you have to do something like what you do in your question. You could write something like:

start_path = '/my/root/directory'
final_path = os.join(start_path, *list_of_vars)
if not os.path.isdir(final_path):
    os.makedirs (final_path)

Can I have H2 autocreate a schema in an in-memory database?

If you are using Spring Framework with application.yml and having trouble to make the test find the SQL file on the INIT property, you can use the classpath: notation.

For example, if you have a init.sql SQL file on the src/test/resources, just use:

url=jdbc:h2:~/test;INIT=RUNSCRIPT FROM 'classpath:init.sql';DB_CLOSE_DELAY=-1;

Difference between /res and /assets directories

Use assets like a filesystem to dump any kind of files. And use res to store what it is made for, layouts, images, values.

jQuery - find table row containing table cell containing specific text

This will search text in all the td's inside each tr and show/hide tr's based on search text

 $.each($(".table tbody").find("tr"), function () {                              

                if ($(this).text().toLowerCase().replace(/\s+/g, '').indexOf(searchText.replace(/\s+/g, '').toLowerCase()) == -1)

Android studio - Failed to find target android-18

I had the same problem when trying out Android Studio. I already had projects running on the ADT under SDK 18. No need to hack the manifest files.

Fixed by:

export ANDROID_HOME= pathtobundle/adt-bundle-linux-x86_64-20130729/sdk

If you don't have the ADT installed, and just want the SDK, it seems like a good solution is to install everything and then point Android Studio to the just the packaged SDK.

cd pathtobundle


unzip *.zip

As someone else said, you may need to run the SDK Manager to install the desired packages before running Studio.

Find empty or NaN entry in Pandas Dataframe

To obtain all the rows that contains an empty cell in in a particular column.


This will give the subset of DF_raw, which satisfy the checking condition.

How to fix homebrew permissions?

cd /usr/local && sudo chown -R $(whoami) bin etc include lib sbin share var opt Cellar Frameworks

WAMP shows error 'MSVCR100.dll' is missing when install

For me none of the above answers worked so I am adding what worked for me. I first installed the files mentioned in the accepted answer and when that not worked, I downloaded files from this link and it started working.

So I think 2012 distribution is also needed (I am using window7 home basic 64 FYI).

Define variable to use with IN operator (T-SQL)

No, there is no such type. But there are some choices:

  • Dynamically generated queries (sp_executesql)
  • Temporary tables
  • Table-type variables (closest thing that there is to a list)
  • Create an XML string and then convert it to a table with the XML functions (really awkward and roundabout, unless you have an XML to start with)

None of these are really elegant, but that's the best there is.

Rolling or sliding window iterator?

a slightly modified version of the deque window, to make it a true rolling window. So that it starts being populated with just one element, then grows to it's maximum window size, and then shrinks as it's left edge comes near the end:

from collections import deque
def window(seq, n=2):
    it = iter(seq)
    win = deque((next(it, None) for _ in xrange(1)), maxlen=n)
    yield win
    append = win.append
    for e in it:
        yield win
    for _ in xrange(len(win)-1):
        yield win

for wnd in window(range(5), n=3):

this gives

[0, 1]
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
[3, 4]

How can I switch themes in Visual Studio 2012

Also, you can use or create and share Visual Studio color schemes:

Grouping switch statement cases together?

No, unless you want to break compatibility and your compiler supports it.

Why is MySQL InnoDB insert so slow?

things that speed up the inserts:

  • i had removed all keys from a table before large insert into empty table
  • then found i had a problem that the index did not fit in memory.
  • also found i had sync_binlog=0 (should be 1) even if binlog is not used.
  • also found i did not set innodb_buffer_pool_instances

Spring MVC 4: "application/json" Content Type is not being set correctly

Not exactly for this OP, but for those who encountered 404 and cannot set response content-type to "application/json" (any content-type). One possibility is a server actually responds 406 but explorer (e.g., chrome) prints it as 404.

If you do not customize message converter, spring would use It would run:

List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request);
List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType);

and if they do not have any overlapping (the same item), it would throw HttpMediaTypeNotAcceptableException and this finally causes 406. No matter if it is an ajax, or GET/POST, or form action, if the request uri ends with a .html or any suffix, the requestedMediaTypes would be "text/[that suffix]", and this conflicts with producibleMediaTypes, which is usually:


Use Font Awesome Icons in CSS

I am bit late to the part. Just like to suggest another way.

  button.calendar::before {
    content: '\f073';
    font-family: 'Font Awesome 5 Free';
    left: -4px;
    bottom: 4px;
    position: relative;

position,left and bottom is used to align icon.

Sometimes adding font-weight 600 or above also helps.

AngularJS ng-click to go to another page (with Ionic framework)

app.controller('NavCtrl', function ($scope, $location, $state, $window, Post, Auth) {
    $ = {url: 'http://', title: ''};

    $scope.createVariable = function(url) {
      $window.location.href = url;
    $scope.createFixed = function() {
      $window.location.href = '/tab/newpost';


<button class="button button-icon ion-compose" ng-click="createFixed()"></button>
<button class="button button-icon ion-compose" ng-click="createVariable('/tab/newpost')"></button>

Fatal error in launcher: Unable to create process using ""C:\Program Files (x86)\Python33\python.exe" "C:\Program Files (x86)\Python33\pip.exe""

I have chosen to install Python for Windows (64bit) not for all users, but just for me.

Reinstalling Python-x64 and checking the advanced option "for all users" solved the pip problem for me.

Sort a list of numerical strings in ascending order

in python sorted works like you want with integers:

>>> sorted([10,3,2])
[2, 3, 10]

it looks like you have a problem because you are using strings:

>>> sorted(['10','3','2'])
['10', '2', '3']

(because string ordering starts with the first character, and "1" comes before "2", no matter what characters follow) which can be fixed with key=int

>>> sorted(['10','3','2'], key=int)
['2', '3', '10']

which converts the values to integers during the sort (it is called as a function - int('10') returns the integer 10)

and as suggested in the comments, you can also sort the list itself, rather than generating a new one:

>>> l = ['10','3','2']
>>> l.sort(key=int)
>>> l
['2', '3', '10']

but i would look into why you have strings at all. you should be able to save and retrieve integers. it looks like you are saving a string when you should be saving an int? (sqlite is unusual amongst databases, in that it kind-of stores data in the same type as it is given, even if the table column type is different).

and once you start saving integers, you can also get the list back sorted from sqlite by adding order by ... to the sql command:

select temperature from temperatures order by temperature;

Putting -moz-available and -webkit-fill-available in one width (css property)

I needed my ASP.NET drop down list to take up all available space, and this is all I put in the CSS and it is working in Firefox and IE11:

width: 100%

I had to add the CSS class into the asp:DropDownList element

Laravel 5: Display HTML with Blade

You can use {!! $text !!} for render HTML code in Laravel

{!! $text !!}

If you use

{{ $text }}

It will not render HTML code and print as a string.

Adding devices to team provisioning profile

Update for Xcode (Version 9.1). Please follow below steps for refreshing Provisioning profiles

Using Xcode Organizer

  • Select Export

enter image description here

  • Select desired distribution facility

enter image description here

  • Now Select Automatically Manage Signing Identity enter image description here
  • In next Screen Please click on Profile tag detail discloser button which will navigate you to Provisioning profile Folder

enter image description here

  • Select all profiles and trash them. Now in Xcode click on the Previous button and click again on Automatically Manage Signing, Now Xcode will create new signing identity for you with latest features (including new device id's)

In short, you can navigate to MobileDevice/Provisioning Profiles/ folder path and delete all profiles and then Archive. Now you can see there are new profiles for you. Cheers :)

@JasonH hope it will help you.

twig: IF with multiple conditions

If I recall correctly Twig doesn't support || and && operators, but requires or and and to be used respectively. I'd also use parentheses to denote the two statements more clearly although this isn't technically a requirement.

{%if ( fields | length > 0 ) or ( trans_fields | length > 0 ) %}


Expressions can be used in {% blocks %} and ${ expressions }.

Operator    Description
==          Does the left expression equal the right expression?
+           Convert both arguments into a number and add them.
-           Convert both arguments into a number and substract them.
*           Convert both arguments into a number and multiply them.
/           Convert both arguments into a number and divide them.
%           Convert both arguments into a number and calculate the rest of the integer division.
~           Convert both arguments into a string and concatenate them.
or          True if the left or the right expression is true.
and         True if the left and the right expression is true.
not         Negate the expression.

For more complex operations, it may be best to wrap individual expressions in parentheses to avoid confusion:

{% if (foo and bar) or (fizz and (foo + bar == 3)) %}

Android: Scale a Drawable or background image?

One option to try is to put the image in the drawable-nodpi folder and set background of a layout to the drawable resource id.

This definitely works with scaling down, I haven't tested with scaling up though.

Python: Converting from ISO-8859-1/latin1 to UTF-8

Decode to Unicode, encode the results to UTF8.


How to make button look like a link?

button {_x000D_
  background: none!important;_x000D_
  border: none;_x000D_
  padding: 0!important;_x000D_
  font-family: arial, sans-serif;_x000D_
  /*input has OS specific font-family*/_x000D_
  color: #069;_x000D_
  text-decoration: underline;_x000D_
  cursor: pointer;_x000D_
<button> your button that looks like a link</button>

What and When to use Tuple?

Tuple classes allow developers to be 'quick and lazy' by not defining a specific class for a specific use.

The property names are Item1, Item2, Item3 ..., which may not be meaningful in some cases or without documentation.

Tuple classes have strongly typed generic parameters. Still users of the Tuple classes may infer from the type of generic parameters.

How to check whether particular port is open or closed on UNIX?

netstat -ano|grep 443|grep LISTEN

will tell you whether a process is listening on port 443 (you might have to replace LISTEN with a string in your language, though, depending on your system settings).

How to scanf only integer and repeat reading if the user enters non-numeric characters?

You will need to repeat your call to strtol inside your loops where you are asking the user to try again. In fact, if you make the loop a do { ... } while(...); instead of while, you don't get a the same sort of repeat things twice behaviour.

You should also format your code so that it's possible to see where the code is inside a loop and not.

Change <select>'s option and trigger events with JavaScript

Fiddle of my solution is here. But just in case it expires I will paste the code as well.


<select id="sel">
  <option value='1'>One</option>
  <option value='2'>Two</option>
  <option value='3'>Three</option>
<input type="button" id="button" value="Change option to 2" />


var sel = document.getElementById('sel'),
    button = document.getElementById('button');

button.addEventListener('click', function (e) {
    sel.options[1].selected = true;

    // firing the event properly according to StackOverflow
    if ("createEvent" in document) {
        var evt = document.createEvent("HTMLEvents");
        evt.initEvent("change", false, true);
    else {

sel.addEventListener('change', function (e) {

What does $_ mean in PowerShell?

$_ is an alias for automatic variable $PSItem (introduced in PowerShell V3.0; Usage information found here) which represents the current item from the pipe.

PowerShell (v6.0) online documentation for automatic variables is here.

How can I rotate an HTML <div> 90 degrees?

We can add the following to a particular tag in CSS:

-webkit-transform: rotate(90deg);
-moz-transform: rotate(90deg);
-o-transform: rotate(90deg);
-ms-transform: rotate(90deg);
transform: rotate(90deg);

In case of half rotation change 90 to 45.

How to create Custom Ratings bar in Android

You can have 5 imageview with defalut image as star that is empty and fill the rating bar with half or full image base on rating.

 public View getView(int position, View convertView, ViewGroup parent) {
     LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
     View grid=inflater.inflate(R.layout.griditem, parent, false);
     imgoff =(ImageView)grid.findViewById(;
     tv.setPadding(0, 2, 0, 0);
    Float rate=rateFArr[position];

   if(rate==5 || rate==4.5)
    if(rate==4 || rate==3.5)
    if(rate==3 || rate==2.5)
    if(rate==2 || rate==1.5)
    if(rate==1 || rate==0.5)


    // rb=(RatingBar)findViewById(;
        return grid;

How do I pass a datetime value as a URI parameter in mvc?

The colon in your first example's url is going to cause an error (Bad Request) so you can't do exactly what you are looking for. Other than that, using a DateTime as an action parameter is most definitely possible.

If you are using the default routing, this 3rd portion of your example url is going to pickup the DateTime value as the {id} parameter. So your Action method might look like this:

public ActionResult Index(DateTime? id)
    return View();

You'll probably want to use a Nullable Datetime as I have, so if this parameter isn't included it won't cause an exception. Of course, if you don't want it to be named "id" then add another route entry replacing {id} with your name of choice.

As long as the text in the url will parse to a valid DateTime value, this is all you have to do. Something like the following works fine and will be picked up in your Action method without any errors:

<%=Html.ActionLink("link", "Index", new { id = DateTime.Now.ToString("dd-MM-yyyy") }) %>

The catch, in this case of course, is that I did not include the time. I'm not sure there are any ways to format a (valid) date string with the time not represented with colons, so if you MUST include the time in the url, you may need to use your own format and parse the result back into a DateTime manually. Say we replace the colon with a "!" in the actionlink: new { id = DateTime.Now.ToString("dd-MM-yyyy HH!mm") }.

Your action method will fail to parse this as a date so the best bet in this case would probably to accept it as a string:

public ActionResult Index(string id)
    DateTime myDate;
    if (!string.IsNullOrEmpty(id))
        myDate = DateTime.Parse(id.Replace("!", ":"));
    return View();

Edit: As noted in the comments, there are some other solutions arguably better than mine. When I originally wrote this answer I believe I was trying to preserve the essence of the date time format as best possible, but clearly URL encoding it would be a more proper way of handling this. +1 to Vlad's comment.

Dropdown select with images

This is using ms-Dropdown :

But data resource is json.

Example :


<div id="byjson"></div>


        var jsonData = [
            {description:'Choos your payment gateway', value:'', text:'Payment Gateway'},
            {image:'', description:'My life. My card...', value:'amex', text:'Amex'},
            {image:'', description:'It pays to Discover...', value:'Discover', text:'Discover'},
            {image:'', title:'For everything else...', description:'For everything else...', value:'Mastercard', text:'Mastercard'},
            {image:'', description:'Sorry not available...', value:'cash', text:'Cash on devlivery', disabled:true},
            {image:'', description:'All you need...', value:'Visa', text:'Visa'},
            {image:'', description:'Pay and get paid...', value:'Paypal', text:'Paypal'}
        $("#byjson").msDropDown({byJson:{data:jsonData, name:'payments2'}}).data("dd");

Batch File; List files in directory, only filenames?

The full command is:

dir /b /a-d

Let me break it up;

Basically the /b is what you look for.

/a-d will exclude the directory names.

For more information see dir /? for other arguments that you can use with the dir command.

What is the meaning of polyfills in HTML5?

Here are some high level thoughts and info that might help, aside from the other answers.

Pollyfills are like a compatability patch for specific browsers. Shims are changes to specific arguments. Fallbacks can be used if say a @mediaquery is not compatible with a browser.

It kind of depends on the requirements of what your app/website needs to be compatible with.

You cna check this site out for compatability of specific libraries with specific browsers.

Python - converting a string of numbers into a list of int

number_string = '0, 0, 0, 11, 0, 0, 0, 0, 0, 19, 0, 9, 0, 0, 0, 0, 0, 0, 11'

number_string = number_string.split(',')

number_string = [int(i) for i in number_string]

CakePHP find method with JOIN

        $services = $this->Service->find('all', array(
            'limit' =>4,
            'fields' => array('Service.*','ServiceImage.*'),
            'joins' => array(
                        'table' => 'services_images',
                        'alias' => 'ServiceImage',
                        'type' => 'INNER',
                        'conditions' => array(
                        'ServiceImage.service_id' =>''

It goges to array is null.

How can I create a simple index.html file which lists all files/directories?

You can either: Write a server-side script page like PHP, JSP, etc to generate this HTML dynamically


Setup the web-server that you are using (e.g. Apache) to do exactly that automatically for directories that doesn't contain welcome-page (e.g. index.html)

Specifically in apache read more here: Edit the httpd.conf: (updated link:

or add the autoindex mod:

EPPlus - Read Excel Table

Not sure why but none of the above solution work for me. So sharing what worked:

public void readXLS(string FilePath)
    FileInfo existingFile = new FileInfo(FilePath);
    using (ExcelPackage package = new ExcelPackage(existingFile))
        //get the first worksheet in the workbook
        ExcelWorksheet worksheet = package.Workbook.Worksheets[1];
        int colCount = worksheet.Dimension.End.Column;  //get Column Count
        int rowCount = worksheet.Dimension.End.Row;     //get row count
        for (int row = 1; row <= rowCount; row++)
            for (int col = 1; col <= colCount; col++)
                Console.WriteLine(" Row:" + row + " column:" + col + " Value:" + worksheet.Cells[row, col].Value?.ToString().Trim());

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

This may or may not help you address your problem, OP, but to get the timezone of the current server relative to UTC (UT1, technically), do:


The above works by extracting the UT1-relative offset in minutes, and then converting it to hours using the factor of 3600 secs/hour.


SET SESSION timezone TO 'Asia/Kabul';
-- output: 4.5 (as of the writing of this post)


display Java.util.Date in a specific format

How about:

SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");

> 31/05/2011

How to get commit history for just one branch?

The git merge-base command can be used to find a common ancestor. So if my_experiment has not been merged into master yet and my_experiment was created from master you could:

git log --oneline `git merge-base my_experiment master`..my_experiment

setTimeout or setInterval?

The very difference is in their purposes.

   -> executes a function, over and over again, at specified time intervals  

   -> executes a function, once, after waiting a specified number of milliseconds

It's as simple as that

More elaborate details here

Load a UIView from nib in Swift

class func loadFromNib<T: UIView>() -> T {
    let nibName = String(describing: self)
    return Bundle.main.loadNibNamed(nibName, owner: nil, options: nil)![0] as! T

Android studio Gradle icon error, Manifest Merger

The answer of shimi_tap is enough. What to be remembered is that choosing only what you need. Choose from {icon, name, theme, label}. I added tools:replace="android:icon,android:theme", it does not work. I added tools:replace="android:icon,android:theme,android:label,android:name", it does not work. It works when I added tools:replace="android:icon,android:theme,android:label". So find out what the conflict exactly is in your manifest files.

SQL Server: Cannot insert an explicit value into a timestamp column

According to MSDN, timestamp

Is a data type that exposes automatically generated, unique binary numbers within a database. timestamp is generally used as a mechanism for version-stamping table rows. The storage size is 8 bytes. The timestamp data type is just an incrementing number and does not preserve a date or a time. To record a date or time, use a datetime data type.

You're probably looking for the datetime data type instead.

Comprehensive methods of viewing memory usage on Solaris

# echo ::memstat | mdb -k
Page Summary                Pages                MB  %Tot
------------     ----------------  ----------------  ----
Kernel                       7308                57   23%
Anon                         9055                70   29%
Exec and libs                1968                15    6%
Page cache                   2224                17    7%
Free (cachelist)             6470                50   20%
Free (freelist)              4641                36   15%

Total                       31666               247
Physical                    31256               244

How do I enumerate the properties of a JavaScript object?

You can use the for of loop.

If you want an array use:


Ref. Object.keys()

Run Command Line & Command From VBS

The problem is on this line: "cmd.exe /C copy "S:Claims\Sound.wav" "C:\WINDOWS\Media\Sound.wav"

Your first quote next to "S:Claims" ends the string; you need to escape the quotes around your files with a second quote, like this: "cmd.exe /C copy ""S:\Claims\Sound.wav"" ""C:\WINDOWS\Media\Sound.wav"" "

You also have a typo in S:Claims\Sound.wav, should be S:\Claims\Sound.wav.

I also assume the apostrophe before Dim oShell and after Set oShell = Nothing are typos as well.

Convert a String to Modified Camel Case in Java or Title Case as is otherwise called


    static String toCamelCase(String s){
           String[] parts = s.split(" ");
           String camelCaseString = "";
           for (String part : parts){
               if(part!=null && part.trim().length()>0)
              camelCaseString = camelCaseString + toProperCase(part);
                   camelCaseString=camelCaseString+part+" ";   
           return camelCaseString;

        static String toProperCase(String s) {
            String temp=s.trim();
            String spaces="";
            int startCharIndex=s.charAt(temp.indexOf(0));
            temp=temp.substring(0, 1).toUpperCase() +
            spaces+temp.substring(1).toLowerCase()+" ";
            return temp;

  public static void main(String[] args) {
     String string="HI tHiS is   SomE Statement";

How to pretty-print a numpy.array without scientific notation and with given precision?

I often want different columns to have different formats. Here is how I print a simple 2D array using some variety in the formatting by converting (slices of) my NumPy array to a tuple:

import numpy as np
dat = np.random.random((10,11))*100  # Array of random values between 0 and 100
print(dat)                           # Lines get truncated and are hard to read
for i in range(10):
    print((4*"%6.2f"+7*"%9.4f") % tuple(dat[i,:]))

'ssh' is not recognized as an internal or external command

Actually you have 2 problems here: First is that you don't have ssh installed, second is that you don't know how to deploy

Install SSH

It seems that ssh is not installed on your computer.

You can install openssh from here :

Generate your key

Than you will have to geneate your ssh-key. There's a good tutorial about this here:


To deploy, you just have to push your code over git. Something like this:

git push fort master

If you get permission denied, be sure that you have put your public_key in the dashboard in the git tab.


The ssh command gives you access to your remote node. You should have received a password by email and now that you have ssh installed, you should be asked for a password when trying to connect. just input that password. If you want to use your private ssh key to connect to your server rather then typing that password, you can follow this :

Java - JPA - @Version annotation

Version used to ensure that only one update in a time. JPA provider will check the version, if the expected version already increase then someone else already update the entity so an exception will be thrown.

So updating entity value would be more secure, more optimist.

If the value changes frequent, then you might consider not to use version field. For an example "an entity that has counter field, that will increased everytime a web page accessed"

In Perl, what is the difference between a .pm (Perl module) and .pl (Perl script) file?

A .pl is a single script.

In .pm (Perl Module) you have functions that you can use from other Perl scripts:

A Perl module is a self-contained piece of Perl code that can be used by a Perl program or by other Perl modules. It is conceptually similar to a C link library, or a C++ class.

JWT authentication for ASP.NET Web API

In my case the JWT is created by a separate API so ASP.NET need only decode and validate it. In contrast to the accepted answer we're using RSA which is a non-symmetric algorithm, so the SymmetricSecurityKey class mentioned above won't work.

Here's the result.

using Microsoft.IdentityModel.Protocols;
using Microsoft.IdentityModel.Protocols.OpenIdConnect;
using Microsoft.IdentityModel.Tokens;
using System;
using System.IdentityModel.Tokens.Jwt;
using System.Threading;
using System.Threading.Tasks;

    public static async Task<JwtSecurityToken> VerifyAndDecodeJwt(string accessToken)
            var configurationManager = new ConfigurationManager<OpenIdConnectConfiguration>($"{securityApiOrigin}/.well-known/openid-configuration", new OpenIdConnectConfigurationRetriever());
            var openIdConfig = await configurationManager.GetConfigurationAsync(CancellationToken.None);
            var validationParameters = new TokenValidationParameters()
                ValidateLifetime = true,
                ValidateAudience = false,
                ValidateIssuer = false,
                RequireSignedTokens = true,
                IssuerSigningKeys = openIdConfig.SigningKeys,
            new JwtSecurityTokenHandler().ValidateToken(accessToken, validationParameters, out var validToken);
            // threw on invalid, so...
            return validToken as JwtSecurityToken;
        catch (Exception ex)
            return null;

HTML5 live streaming

You can use a fantastic library name Videojs. You will find more useful informations here. But with quick start you can do something like this:

<link href="//" rel="stylesheet">
<script src="//"></script>
class="video-js vjs-default-skin vjs-big-play-centered" 
data-setup='{"techOrder": ["flash", "html5", "other supported tech"], "nativeControlsForTouch": true, "controlBar": { "muteToggle": false, "volumeControl": false, "timeDivider": false, "durationDisplay": false, "progressControl": false } }'
<source src="rtmp://{domain_server}/{publisher}" type='rtmp/mp4'/>
var player = videojs('Video');;

Youtube autoplay not working on mobile devices with embedded HTML5 player

As it turns out, autoplay cannot be done on iOS devices (iPhone, iPad, iPod touch) and Android.

See and

'list' object has no attribute 'shape'

Alternatively, you can use np.shape(...)

For instance:

import numpy as np


and np.shape(a) will give an output of (3,)

SQL multiple columns in IN clause

In general you can easily write the Where-Condition like this:

select * from tab1
where (col1, col2) in (select col1, col2 from tab2)

Oracle ignores rows where one or more of the selected columns is NULL. In these cases you probably want to make use of the NVL-Funktion to map NULL to a special value (that should not be in the values):

select * from tab1
where (col1, NVL(col2, '---') in (select col1, NVL(col2, '---') from tab2)

Is Java "pass-by-reference" or "pass-by-value"?

This is the best way to answer the question imo...

First, we must understand that, in Java, the parameter passing behavior...

public void foo(Object param)
  // some code in foo...

public void bar()
  Object obj = new Object();


is exactly the same as...

public void bar()
  Object obj = new Object();

  Object param = obj;

  // some code in foo...

not considering stack locations, which aren't relevant in this discussion.

So, in fact, what we're looking for in Java is how variable assignment works. I found it in the docs :

One of the most common operators that you'll encounter is the simple assignment operator "=" [...] it assigns the value on its right to the operand on its left:

int cadence = 0;
int speed = 0;
int gear = 1;

This operator can also be used on objects to assign object references [...]

It's clear how this operator acts in two distinct ways: assign values and assign references. The last, when it's an object... the first, when it isn't an object, that is, when it's a primitive. But so, can we understand that Java's function params can be pass-by-value and pass-by-reference?

The truth is in the code. Let's try it:

public class AssignmentEvaluation
  static public class MyInteger
    public int value = 0;

  static public void main(String[] args)
    System.out.println("Assignment operator evaluation using two MyInteger objects named height and width\n");

    MyInteger height = new MyInteger();
    MyInteger width  = new MyInteger();

    System.out.println("[1] Assign distinct integers to height and width values");

    height.value = 9;
    width.value  = 1;

    System.out.println("->  height is " + height.value + " and width is " + width.value + ", we are different things! \n");

    System.out.println("[2] Assign to height's value the width's value");

    height.value = width.value;

    System.out.println("->  height is " + height.value + " and width is " + width.value + ", are we the same thing now? \n");

    System.out.println("[3] Assign to height's value an integer other than width's value");

    height.value = 9;

    System.out.println("->  height is " + height.value + " and width is " + width.value + ", we are different things yet! \n");

    System.out.println("[4] Assign to height the width object");

    height = width;

    System.out.println("->  height is " + height.value + " and width is " + width.value + ", are we the same thing now? \n");

    System.out.println("[5] Assign to height's value an integer other than width's value");

    height.value = 9;

    System.out.println("->  height is " + height.value + " and width is " + width.value + ", we are the same thing now! \n");

    System.out.println("[6] Assign to height a new MyInteger and an integer other than width's value");

    height = new MyInteger();
    height.value = 1;

    System.out.println("->  height is " + height.value + " and width is " + width.value + ", we are different things again! \n");

This is the output of my run:

Assignment operator evaluation using two MyInteger objects named height and width

[1] Assign distinct integers to height and width values
->  height is 9 and width is 1, we are different things! 

[2] Assign to height's value the width's value
->  height is 1 and width is 1, are we the same thing now? 

[3] Assign to height's value an integer other than width's value
->  height is 9 and width is 1, we are different things yet! 

[4] Assign to height the width object
->  height is 1 and width is 1, are we the same thing now? 

[5] Assign to height's value an integer other than width's value
->  height is 9 and width is 9, we are the same thing now! 

[6] Assign to height a new MyInteger and an integer other than width's value
->  height is 1 and width is 9, we are different things again! 

In [2] we have distinct objects and assign one variable's value to the other. But after assigning a new value in [3] the objects had different values, which means that in [2] the assigned value was a copy of the primitive variable, usually called pass-by-value, otherwise, the values printed in [3] should be the same.

In [4] we still have distinct objects and assign one object to the other. And after assigning a new value in [5] the objects had the same values, which means that in [4] the assigned object was not a copy of the other, which should be called pass-by-reference. But, if we look carefully in [6], we can't be so sure that no copy was done... ?????

We can't be so sure because in [6] the objects were the same, then we assigned a new object to one of them, and after, the objects had different values! How can they be distinct now if they were the same? They should be the same here too! ?????

We'll need to remember the docs to understand what's going on:

This operator can also be used on objects to assign object references

So our two variables were storing references... our variables had the same reference after [4] and different references after [6]... if such a thing is possible, this means that assignment of objects is done by copy of the object's reference, otherwise, if it was not a copy of reference, the printed value of the variables in [6] should be the same. So objects (references), just like primitives, are copied to variables through assignment, what people usually call pass-by-value. That's the only pass-by- in Java.

Changing the child element's CSS when the parent is hovered

To change it from css you dont even need to set the child class

.parent > div:nth-child(1) { display:none; }
.parent:hover > div:nth-child(1) { display: block; }

How to increase memory limit for PHP over 2GB?

You should have 64-bit OS on hardware that supports 64-bit OS, 64-bit Apache version and the same for PHP. But this does not guarantee that functions that are work with PDF can use such big sizes of memory. You'd better not load the whole file into memory, split it into chunks or use file functions to seek on it without loading to RAM.

How can I include css files using node, express, and ejs?

I have used the following steps to resolve this problem

  1. create new folder (static) and move all js and css file into this folder.
  2. then add app.use('/static', express.static('static'))
  3. add css like < link rel="stylesheet" type="text/css" href="/static/style.css"/>
  4. restart server to view impact after changes.

Should I use @EJB or @Inject

@Inject can inject any bean, while @EJB can only inject EJBs. You can use either to inject EJBs, but I'd prefer @Inject everywhere.

Why doesn't the Scanner class have a nextChar method?

The reason is that the Scanner class is designed for reading in whitespace-separated tokens. It's a convenience class that wraps an underlying input stream. Before scanner all you could do was read in single bytes, and that's a big pain if you want to read words or lines. With Scanner you pass in, and it does a number of read() operations to tokenize the input for you. Reading a single character is a more basic operation. Source

You can use (char);.

Maven error "Failure to transfer..."

Thanks for the replies, but after some more searching I was able to fix the problem. It turned out that I had to remove one of the "*.lastUpdated" which was preventing one of my plugins (Maven Surefire Plugin) from updating. I did this manually, because a maven clean wasn't doing it apparently.

The problem was that the "*.lastUpdated" file for a plugin was blocking the maven check for updates and not allowing a necessary jar to get downloaded.

Simulate low network connectivity for Android

I'm surprised nobody mentioned this. You can tether via Bluetooth, and separate them by ten+ meters(or less with obstacles). You've got a real bad connection. No microwave, no elevator, no software needed.

Check if element is clickable in Selenium Java

There are certain things you have to take care:

  • WebDriverWait inconjunction with ExpectedConditions as elementToBeClickable() returns the WebElement once it is located and clickable i.e. visible and enabled.
  • In this process, WebDriverWait will ignore instances of NotFoundException that are encountered by default in the until condition.
  • Once the duration of the wait expires on the desired element not being located and clickable, will throw a timeout exception.
  • The different approach to address this issue are:
    • To invoke click() as soon as the element is returned, you can use:

      new WebDriverWait(driver, 10).until(ExpectedConditions.elementToBeClickable(By.xpath("(//div[@id='brandSlider']/div[1]/div/div/div/img)[50]"))).click();
    • To simply validate if the element is located and clickable, wrap up the WebDriverWait in a try-catch{} block as follows:

      try {
             new WebDriverWait(driver, 10).until(ExpectedConditions.elementToBeClickable(By.xpath("(//div[@id='brandSlider']/div[1]/div/div/div/img)[50]")));
             System.out.println("Element is clickable");
      catch(TimeoutException e) {
             System.out.println("Element isn't clickable");
    • If WebDriverWait returns the located and clickable element but the element is still not clickable, you need to invoke executeScript() method as follows:

      WebElement element = new WebDriverWait(driver, 10).until(ExpectedConditions.elementToBeClickable(By.xpath("(//div[@id='brandSlider']/div[1]/div/div/div/img)[50]"))); 
      ((JavascriptExecutor)driver).executeScript("arguments[0].click();", element);

Bootstrap date and time picker

If you are still interested in a javascript api to select both date and time data, have a look at these projects which are forks of bootstrap datepicker:

The first fork is a big refactor on the parsing/formatting codebase and besides providing all views to select date/time using mouse/touch, it also has a mask option (by default) which lets the user to quickly type the date/time based on a pre-specified format.

How do I compare two strings in Perl?

And if you'd like to extract the differences between the two strings, you can use String::Diff.

How should I store GUID in MySQL tables?

I would store it as a char(36).

How to install all required PHP extensions for Laravel?

Laravel Server Requirements mention that BCMath, Ctype, JSON, Mbstring, OpenSSL, PDO, Tokenizer, and XML extensions are required. Most of the extensions are installed and enabled by default.

You can run the following command in Ubuntu to make sure the extensions are installed.

sudo apt install openssl php-common php-curl php-json php-mbstring php-mysql php-xml php-zip

PHP version specific installation (if PHP 7.4 installed)

sudo apt install php7.4-common php7.4-bcmath openssl php7.4-json php7.4-mbstring

You may need other PHP extensions for your composer packages. Find from links below.

PHP extensions for Ubuntu 20.04 LTS (Focal Fossa)

PHP extensions for Ubuntu 18.04 LTS (Bionic)

PHP extensions for Ubuntu 16.04 LTS (Xenial)

Is there a way to add a gif to a Markdown file?

just upload the .gif file into your base folder of GitHub and edit just use this code


DataTables: Uncaught TypeError: Cannot read property 'defaults' of undefined

var datatable_jquery_script = document.createElement("script");
datatable_jquery_script.src = "vendor/datatables/jquery.dataTables.min.js";
    var datatable_bootstrap_script = document.createElement("script");
    datatable_bootstrap_script.src = "vendor/datatables/dataTables.bootstrap4.min.js";

I used setTimeOut to make sure datatables.min.js loads first. I inspected the waterfall loading of each, bootstrap4.min.js always loads first.

Removing input background colour for Chrome autocomplete?

Google Chrome user agent prevent developers' CSS, So for changing autofill UI must use another property like these:

select:-webkit-autofill {
    -webkit-box-shadow: 0 0 0 1000px #d500ff inset !important;
    /*use inset box-shadow to cover background-color*/
    -webkit-text-fill-color: #ffa400 !important;
    /*use text fill color to cover font color*/

Bundle ID Suffix? What is it?

If you don't have a company, leave your name, it doesn't matter as long as both bundle id in info.plist file and the one you've submitted in iTunes Connect match.

In Bundle ID Suffix you should write full name of bundle ID.


Bundle ID suffix = thebestapp (NOT CORRECT!!!!)

Bundle ID suffix = com.awesomeapps.thebestapp (CORRECT!!)

The reason for this is explained in the Developer Portal:

The App ID string contains two parts separated by a period (.) — an App ID Prefix (your Team ID by default, e.g. ABCDE12345), and an App ID Suffix (a Bundle ID search string, e.g. com.mycompany.appname). [emphasis added]

So in this case the suffix is the full string com.awesomeapps.thebestapp.

ERROR 1396 (HY000): Operation CREATE USER failed for 'jack'@'localhost'

If you want to delete a user with sql, you need to delete the related data in these tables: columns_priv, db, procs_priv, tables_priv. Then execute flush privileges;

How do you get the magnitude of a vector in Numpy?

You can do this concisely using the toolbelt vg. It's a light layer on top of numpy and it supports single values and stacked vectors.

import numpy as np
import vg

x = np.array([1, 2, 3, 4, 5])
mag1 = np.linalg.norm(x)
mag2 = vg.magnitude(x)
print mag1 == mag2
# True

I created the library at my last startup, where it was motivated by uses like this: simple ideas which are far too verbose in NumPy.

Calling one method from another within same class in Python

To accessing member functions or variables from one scope to another scope (In your case one method to another method we need to refer method or variable with class object. and you can do it by referring with self keyword which refer as class object.

class YourClass():

    def your_function(self, *args):

        self.callable_function(param) # if you need to pass any parameter

    def callable_function(self, *params): 
        print('Your param:', param)

Make Error 127 when running trying to compile code

Error 127 means one of two things:

  1. file not found: the path you're using is incorrect. double check that the program is actually in your $PATH, or in this case, the relative path is correct -- remember that the current working directory for a random terminal might not be the same for the IDE you're using. it might be better to just use an absolute path instead.
  2. ldso is not found: you're using a pre-compiled binary and it wants an interpreter that isn't on your system. maybe you're using an x86_64 (64-bit) distro, but the prebuilt is for x86 (32-bit). you can determine whether this is the answer by opening a terminal and attempting to execute it directly. or by running file -L on /bin/sh (to get your default/native format) and on the compiler itself (to see what format it is).

if the problem is (2), then you can solve it in a few diff ways:

  1. get a better binary. talk to the vendor that gave you the toolchain and ask them for one that doesn't suck.
  2. see if your distro can install the multilib set of files. most x86_64 64-bit distros allow you to install x86 32-bit libraries in parallel.
  3. build your own cross-compiler using something like crosstool-ng.
  4. you could switch between an x86_64 & x86 install, but that seems a bit drastic ;).

Arrays in unix shell?

in bash, you create array like this

arr=(one two three)

to call the elements

$ echo "${arr[0]}"
$ echo "${arr[2]}"

to ask for user input, you can use read

read -p "Enter your choice: " choice

How do I use .toLocaleTimeString() without displaying seconds?

Even though this is an older question, I had the same one myself recently, and came up with a more simple solution using regular expressions and the string replace function as another alternative (no need for external js libraries or reliance on the ECMAScript Internalization API):

var d = new Date();
var localeTime = d.toLocaleTimeString();
var localeTimeSansSeconds = localeTime.replace(/:(\d{2}) (?=[AP]M)/, " ");

This approach uses a regex look-ahead to grab the :ss AM/PM end of the string and replaces the :ss part with a space, returning the rest of the string untouched. (Literally says "Find a colon with two digits and a space that is followed by either AM or PM and replace the colon, two digits, and space portion with just a space).

This expression/approach only works for en-US and en-US-like Locales. If you also wanted a similar outcome with, say, British English (en-GB), which doesn't use AM/PM, a different regular expression is needed.

Based on the original questioner's sample output, I assume that they were primarily dealing with American audiences and the en-US time schema.

recursively use scp but excluding some folders

Assuming the simplest option (installing rsync on the remote host) isn't feasible, you can use sshfs to mount the remote locally, and rsync from the mount directory. That way you can use all the options rsync offers, for example --exclude.

Something like this should do:

sshfs user@server: sshfsdir
rsync --recursive --exclude=whatever sshfsdir/path/on/server /where/to/store

Note that the effectiveness of rsync (only transferring changes, not everything) doesn't apply here. This is because for that to work, rsync must read every file's contents to see what has changed. However, as rsync runs only on one host, the whole file must be transferred there (by sshfs). Excluded files should not be transferred, however.

String MinLength and MaxLength validation don't work ( mvc)

This can replace the MaxLength and the MinLength

[StringLength(40, MinimumLength = 10 , ErrorMessage = "Password cannot be longer than 40 characters and less than 10 characters")]

Jquery select this + class

Use find()


How can I alter a primary key constraint using SQL syntax?

Yes. The only way would be to drop the constraint with an Alter table then recreate it.

ALTER TABLE <Table_Name>
DROP CONSTRAINT <constraint_name>

ALTER TABLE <Table_Name>
ADD CONSTRAINT <constraint_name> PRIMARY KEY (<Column1>,<Column2>)

ASP.NET MVC 404 Error Handling

Looks like this is the best way to catch everything.

How can I properly handle 404 in ASP.NET MVC?

How do I test if a variable is a number in Bash?

The following solution can also be used in basic shells such as Bourne without the need for regular expressions. Basically any numeric value evaluation operations using non-numbers will result in an error which will be implicitly considered as false in shell:

"$var" -eq "$var"

as in:



if [ -n "$var" ] && [ "$var" -eq "$var" ] 2>/dev/null; then
  echo number
  echo not a number

You can can also test for $? the return code of the operation which is more explicit:

[ -n "$var" ] && [ "$var" -eq "$var" ] 2>/dev/null
if [ $? -ne 0 ]; then
   echo $var is not number

Redirection of standard error is there to hide the "integer expression expected" message that bash prints out in case we do not have a number.

CAVEATS (thanks to the comments below):

  • Numbers with decimal points are not identified as valid "numbers"
  • Using [[ ]] instead of [ ] will always evaluate to true
  • Most non-Bash shells will always evaluate this expression as true
  • The behavior in Bash is undocumented and may therefore change without warning
  • If the value includes spaces after the number (e.g. "1 a") produces error, like bash: [[: 1 a: syntax error in expression (error token is "a")
  • If the value is the same as var-name (e.g. i="i"), produces error, like bash: [[: i: expression recursion level exceeded (error token is "i")

How can I inspect element in an Android browser?

Chrome on Android makes it possible to use the Chrome developer tools on the desktop to inspect the HTML that was loaded from the Chrome application on the Android device.


One or more types required to compile a dynamic expression cannot be found. Are you missing references to Microsoft.CSharp.dll and System.Core.dll?

For me, removing and re-adding a reference to Microsoft.CSharp fixed the problem temporarily until the affected file was edited. Closing Visual Studio and reopening the project fixed it more long-term, so that's an option if this situation occurs while Microsoft.CSharp is already referenced.

Maybe restarting the IDE as a first step seems trivial, but here's a reminder for people like me who don't think of that as the first thing to do.