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:
find
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.find(2)
# => #<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
User.first
#find last, the last methods finds the last record ordered by primary key(defult).
#For example:
User.find(:last, *args)
#find last shortcut
User.last
#find all
User.all(:all, *args)
#find all shortcut
User.all
find_by
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:
User.find_by_username("Qing")
Summary
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.