alias method chain in a module

alias_method_chain is a neat little method that lets you cleanly override a core method in Rails. But I ran into syntax problems using it in a module. Here's the solution.

Given:

file: models/foo.rb

class Foo < ActiveRecord::Base

  include FooBar

end

file: lib/foo_bar.rb

module FooBar

  module ClassMethods

    def find_with_bar( *args ) 

      find_without_bar( *args )

      #...or whatever 

    end

  end

  def self.included(base)

    base.class_eval do

      extend ClassMethods

      class << self

        alias_method_chain :find, :bar

      end

    end

  end

end

The alias_method_chain will alias the original find to find_without_bar, and will alias find_with_bar to find.

The self.included method is called when the module is included in the Foo class. It extends the class methods with those defined in module ClassMethods. And then it does the alias_method_chain, on the Foo class (class << self).