find vs find by vs where

Question

I am new to rails  What I see that there are a lot of ways to find a record    find by  lt columnname gt   lt columnvalue gt   find  first   conditions   gt     lt columnname gt    gt   lt columnvalue gt    where  lt columnname gt    gt   lt columnvalue gt   first   And it looks like all of them end up generating exactly the same SQL  Also  I believe the same is true for finding multiple records    find all by  lt columnname gt   lt columnvalue gt   find  all   conditions   gt     lt columnname gt    gt   lt columnvalue gt    where  lt columnname gt    gt   lt columnvalue gt     Is there a rule of thumb or recommendation on which one to use

User · Answer

The accepted answer generally covers it all, but I'd like to add something, just incase you are planning to work with the model in a way like updating, and you are retrieving a single record(whose id you do not know), Then find_by is the way to go, because it retrieves the record and does not put it in an array

irb(main):037:0> @kit = Kit.find_by(number: "3456")
  Kit Load (0.9ms)  SELECT "kits".* FROM "kits" WHERE "kits"."number" = 
 '3456' LIMIT 1
=> #<Kit id: 1, number: "3456", created_at: "2015-05-12 06:10:56",   
updated_at: "2015-05-12 06:10:56", job_id: nil>

irb(main):038:0> @kit.update(job_id: 2)
(0.2ms)  BEGIN Kit Exists (0.4ms)  SELECT 1 AS one FROM "kits" WHERE  
("kits"."number" = '3456' AND "kits"."id" != 1) LIMIT 1 SQL (0.5ms)   
UPDATE "kits" SET "job_id" = $1, "updated_at" = $2 WHERE  "kits"."id" = 
1  [["job_id", 2], ["updated_at", Tue, 12 May 2015 07:16:58 UTC +00:00]] 
(0.6ms)  COMMIT => true

but if you use where then you can not update it directly

irb(main):039:0> @kit = Kit.where(number: "3456")
Kit Load (1.2ms)  SELECT "kits".* FROM "kits" WHERE "kits"."number" =  
'3456' => #<ActiveRecord::Relation [#<Kit id: 1, number: "3456", 
created_at: "2015-05-12 06:10:56", updated_at: "2015-05-12 07:16:58", 
job_id: 2>]>

irb(main):040:0> @kit.update(job_id: 3)
ArgumentError: wrong number of arguments (1 for 2)

in such a case you would have to specify it like this

irb(main):043:0> @kit[0].update(job_id: 3)
(0.2ms)  BEGIN Kit Exists (0.6ms)  SELECT 1 AS one FROM "kits" WHERE 
("kits"."number" = '3456' AND "kits"."id" != 1) LIMIT 1 SQL (0.6ms)   
UPDATE "kits" SET "job_id" = $1, "updated_at" = $2 WHERE "kits"."id" = 1  
[["job_id", 3], ["updated_at", Tue, 12 May 2015 07:28:04 UTC +00:00]]
(0.5ms)  COMMIT => true

User · Answer

Both  2s in your lists are being deprecated  You can still use find params  id   though  Generally  where   works in most situations  Here s a great post  https   web archive org web 20150206131559 http   m onkey org active-record-query-interface

User · Answer

There is a difference between find and find by in that find will return an error if not found  whereas find by will return null    Sometimes it is easier to read if you have a method like find by email   haha   as opposed to  where email  some params  first

User · Answer

Apart from accepted answer  following is also valid  Model find   can accept array of ids  and will return all records which matches  Model find by id 123  also accept array but will only process first id value present in array  Model find  1 2 3   Model find by id  1 2 3

User · Answer

The answers given so far are all OK   However  one interesting difference is that Model find searches by id  if found  it returns a Model object  just a single record  but throws an ActiveRecord  RecordNotFound otherwise   Model find by is very similar to Model find and lets you search any column or group of columns in your database but it returns nil if no record matches the search   Model where on the other hand returns a Model  ActiveRecord Relation object which is just like an array containing all the records that match the search  If no record was found  it returns an empty Model  ActiveRecord Relation object   I hope these would help you in deciding which to use at any point in time

User · Answer

where returns ActiveRecord  Relation  Now take a look at find by implementation   def find by   where  args  take end   As you can see find by is the same as where but it returns only one record  This method should be used for getting 1 record and where should be used for getting all records with some conditions

User · Answer

I will personally recommend using   where  lt  columnname gt    gt   lt  columnvalue gt

User · Answer

The best part of working with any open source technology is that you can inspect length and breadth of it  Checkout this link  find by    Finds the first record matching the specified conditions  There is no implied ordering so if order matters  you should specify it yourself  If no record is found  returns nil   find    Finds the first record matching the specified conditions   but if no record is found  it raises an exception but that is done deliberately   Do checkout the above link  it has all the explanation and use cases for the following two functions

User · Answer

Edit  This answer is very old and other  better answers have come up since this post was made   I d advise looking at the one posted below by  Hossam Khamis for more details  Use whichever one you feel suits your needs best  The find method is usually used to retrieve a row by ID  Model find 1   It s worth noting that find will throw an exception if the item is not found by the attribute that you supply   Use where  as described below  which will return an empty array if the attribute is not found  to avoid an exception being thrown  Other uses of find are usually replaced with things like this  Model all Model first  find by is used as a helper when you re searching for information within a column  and it maps to such with naming conventions   For instance  if you have a column named name in your database  you d use the following syntax  Model find by name   quot Bob quot     where is more of a catch all that lets you use a bit more complex logic for when the conventional helpers won t do  and it returns an array of items that match your conditions  or an empty array otherwise

User · Answer

Suppose I have a model User   User find id    Returns a row where primary key   id  The return type will be User object    User find by email  abc xyz com     Returns first row with matching attribute or email in this case  Return type will be User object again   Note  - User find by email   abc xyz com   is similar to User find by email  abc xyz com     User where project id 1    Returns all users in users table where attribute matches   Here return type will be ActiveRecord  Relation object  ActiveRecord  Relation class includes Ruby s Enumerable module so you can use it s object like an array and traverse on it

User · Answer

Model find  1- Parameter  ID of the object to find   2- If found  It returns the object  One object only    3- If not found  raises an ActiveRecord  RecordNotFound exception   Model find by  1- Parameter  key value   Example   User find by name   John   email   john doe com    2- If found  It returns the object   3- If not found  returns nil   Note  If you want it to raise ActiveRecord  RecordNotFound use find by   Model where  1- Parameter  same as find by  2- If found  It returns ActiveRecord  Relation containing one or more records matching the parameters   3- If not found  It return an Empty ActiveRecord  Relation

User · Answer

Since Rails 4 you can do   User find by name   Bob     which is the equivalent find by name in Rails 3   Use  where when  find and  find by are not enough

[ruby-on-rails] find vs find_by vs where

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