define-a-set-of-class-methods.md

Define A Set Of Class Methods

The most common way to define class methods is by defining them directly with self (the class in the current context) on a method by method basis:

class User
  def self.find_by(attrs)
    # lookup logic ...
  end
end

If you have a group of class methods you want to define, you can stick them all within a class << self block which does similarly defines each of them as singleton methods of that class (User in this case):

class User
  class << self
    def find_by_email(email)
      # lookup logic ...
    end

    def find_by_last_name(last_name)
      # lookup logic ...
    end
  end
end

This opens the singleton class of User for modification, adding these two new methods.

We can see those defined alongside all other direct and inherited class methods:

> User.methods
=>
[:find_by_email,
 :find_by_last_name,
 :yaml_tag,
 :allocate,
 ...
]