railsでscopeがnilを返すとallが返る #Ruby

railsのscope

文字通り、そのクラスの一部のインスタンスを返します
意外と知られてないですが、nilを返すとallが返ります
クラスメソッドと全く同じ挙動ではない。classメソッドはnilを返せばnilが返る

scope


[1] pry(main)> class User < ApplicationRecord
[1] pry(main)*   scope :nil_scope, ->() {  
[1] pry(main)*     nil    
[1] pry(main)*   }    
[1] pry(main)* end  
=> :nil_scope
[2] pry(main)> User.nil_scope
  User Load (4.0ms)  SELECT `users`.* FROM `users`
=> [#<User id: 1, email: "xxx@gmail.com", created_at: "2018-04-14 12:05:50", updated_at: "2019-09-05 01:01:24", provider: "facebook", uid: ...]

pry(main)> User.nil_scope.size
   (0.9ms)  SELECT COUNT(*) FROM `users`
=> 355

class method

[1] pry(main)> class User < ApplicationRecord
[1] pry(main)*   def self.nil_scope
[1] pry(main)*     nil
[1] pry(main)*   end  
[1] pry(main)* end  
=> :nil_scope
[2] pry(main)> User.nil_scope
=> nil