Question

I am writing my first Rails gem, which adds a method to ActiveRecord. I can’t seem to figure out a simple way to call other methods from within the method I am adding to ActiveRecord. Is there a pattern for this I should be using?

module MyModule

  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods

    def my_class_method
      # This doesn't work
      some_utility_method
    end

  end

  def some_utility_method
    # Do something useful
  end

end

ActiveRecord::Base.send(:include, MyModule)

Answer 1

Once you’ve included MyModule, ActiveRecord::Base will have my_class_method as a class method (equivalently, an instance method of the Class object ActiveRecord::Base), and some_utility_method as an instance method.

So, inside my_class_method, self is the Class ActiveRecord::Base, not an instance of that class; it does not have some_utility_method as an available method

Edit:
If you want a utility method private to the Module, you could do it like this:

module MyModule

  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods

    def my_class_method
      # This doesn't work
      MyModule::some_utility_method
    end

  end

  def self.some_utility_method
    # Do something useful
  end

end

ActiveRecord::Base.send(:include, MyModule)