Ching Wang

find VS find_by in Ruby

Notes to myself

I’ve been reviewing ruby and ruby on rails that I’ve learnt a few months ago. There are a few concepts that I would like to write down to refresh my knowledge of ruby.

find and find_by are both ActiveRecord methods for CRUD. According to Activerecord Doc, CRUD is an acronym for the four verbs we use to operate on data: Create, Read, Update and Delete. Active Record automatically creates methods to allow an application to read and manipulate data stored within its tables.

The difference between find and find_by:

find will return an error if not found

find_by will return nil

Let’s have a look at them with examples:


The find method will raise an ActiveRecord::RecordNotFound exception unless a matching record is found for all of the supplied primary keys. Find operates with four different retrieval approaches: find(*args)

#find the user with id 1
# => #<User id: 1, username: "Qing" >

#find first, #find first, the last methods finds the first record ordered by primary key(default).
#For example:
User.find(:first, *args)
#find first shortcut

#find last, the last methods finds the last record ordered by primary key(defult).
#For example:
User.find(:last, *args)
#find last shortcut

#find all
User.all(:all, *args)
#find all shortcut


The find_by method finds the first record matching some conditions. For example:

User.find_by(username: 'Qing')
# => #<User id: 1, username: "Qing">

User.find_by(username: 'Jenny')
# => nil

#The above code is equivalent as below:


The find(id) raises ActiveRecord::RecordNotFound exception when the record does not exist, whereas, the finder find_by(id: id) returns nil. Therefore, I would use use find_by(id: id) to avoid catching exceptions.