重新打开一个由gem提供的ActiveRecord模型'。[英] Re-open an ActiveRecord model that's provided by a gem

问题描述

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?

推荐答案

[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)

其他推荐答案

A word of caution: this is a very old gem (last commit is 3 years old) and by the looks of it won't work with rails 3.x as is. In Rails 3.x engines makes this sort of stuff way easier.

As I understand it the problem in the first case is not that the vote model gets reloaded (it shouldn't) but that the activity_stream_event model is reloaded. Because the vote model isn't reloaded the association is left hanging onto the version of the activity_stream_event class from before the reload. Since rails guts out classes before they get reloaded, this causes problems.

With this in mine, try this hack:

#in config/initializers/abstract_vote.rb
AbstractVote = Vote
AbstractVote.abstract_class= true
Object.send :remove_const, :Vote

#in app/models/vote.rb

class Vote < AbstractVote
  after_create :create_activity_stream_event
  has_one :activity_stream_event

  def create_activity_stream_event
  end
end

What this does is allow you to have your own Vote class that inherits from the one in the gem.

But again, I urge you to find something more up to date or roll your own (the gem is only ~250 lines of ruby)

其他推荐答案

I'd try what agmcleod suggested in the comments but instead of putting it in lib, put it in config/initializers/vote.rb:

 class Vote
   after_create :create_activity_stream_event
   has_one :activity_stream_event

   def create_activity_stream_event
   # something..
   end
 end

Of course, you could fork the gem, make your modifications and link to your forked version in your Gemfile (that's my preference).