Re-open an ActiveRecord model that's provided by a gem

Question

I'm trying to extend an ActiveRecord model (Vote) that a gem (https://github.com/peteonrails/vote_fu) provides to my application. (I.e., there is no vote.rb in app/models)

My first approach was to create a file called lib/extend_vote.rb that contains the code:

Vote.class_eval do
  after_create :create_activity_stream_event
  has_one :activity_stream_event

  def create_activity_stream_event
    # something..
  end
end

This works when the first vote is created, but when I try to create each subsequent vote I get the error TypeError (can't dup NilClass).

I think this error is caused by the fact that the Vote class is reloaded automatically after every request, but the code in lib/extend_vote.rb is loaded only once when the server starts and this causes the has_one :activity_stream_event association to behave weirdly. (Also, the problem goes away if I set config.cache_classes = true in development.rb)

To solve this problem, I tried to make the vote extensions reload on every request by adding a to_prepare block to my development.rb:

config.to_prepare do
  load 'extend_vote.rb'
end

This solves the (can't dup NilClass) problem, but now whenever I create a new vote, the create_activity_stream_event callback gets called an additional time. I.e., the first vote calls it once, the second calls it twice, etc, etc. So it seems like the to_prepare block is reloading the extension TOO aggressively and adding duplicate callbacks.

What's the best way to add methods and callbacks to this Vote model?

Answer 1

[UPDATE: should be the right solution to prevent the module being include several times in the same class]

I believe you can use ActiveSupport::Concern to prevent the module being include several times which result by callback called several time. See the example below :

module VotePatch
  extend ActiveSupport::Concern

  included do
    after_create :create_activity_stream_event
    has_one :activity_stream_event
  end

  module InstanceMethods
    def create_activity_stream_event
      #your code here
    end  
  end

end

Vote.send(:include, VotePatch)