ruby-on-rails - How to add functionality to Mongoid::Document from a gem?

Question

I want to create a gem which adds some functionality to my models. How to define a custom keyword for a Mongoid model? E.g.:

class Book
  include Mongoid::Document

  has_my_awesome_functionality
end

Answer 1

If you have a gem called foobar you can put the following into your gem's initialiser, or in a separate file (usually called railtie.rb[, just make sure it's being loaded]):

require 'foobar'
require 'rails'

class FooBar
  class Railtie < Rails::Railtie

  config.before_initialize do
    ::Mongoid::Document.module_eval do
      def self.included(base)
        base.extend FooBar::MongoidExtension
      end
    end
  end if defined?(Mongoid)
end

and your extension can look like this:

module Foobar::MongoidExtension
  def has_my_awesome_functionality
    # logic here
  end
end