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

问题描述

我正在尝试扩展一个 ActiveRecord 模型 (Vote)，它是一个 gem (https://github.com/peteonrails/vote_fu) 提供给我的应用程序.(即，app/models 中没有 vote.rb)

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)

我的第一个方法是创建一个名为 lib/extend_vote.rb 的文件，其中包含代码:

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

这在创建第一个投票时有效，但是当我尝试创建每个后续投票时，我收到错误 TypeError (can't dup NilClass).

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).

我认为这个错误是由于 Vote 类在每次请求后自动重新加载，但 lib/extend_vote.rb 中的代码只加载一次当服务器启动时，这会导致 has_one :activity_stream_event 关联行为异常.(此外，如果我在 development.rb 中设置 config.cache_classes = true ，问题就会消失)

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)

为了解决这个问题，我试图通过在我的 development.rb 中添加一个 to_prepare 块来重新加载每个请求的投票扩展:

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

这解决了 (can't dup NilClass) 问题，但是现在每当我创建一个新投票时，create_activity_stream_event 回调都会被额外调用一次.即，第一次投票调用它一次，第二次调用它两次，等等.所以看起来 to_prepare 块太积极地重新加载扩展并添加重复的回调.

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.

向这个 Vote 模型添加方法和回调的最佳方法是什么?

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

推荐答案

[更新:应该是防止模块被多次包含在同一个类中的正确解决方案]

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

我相信你可以使用 ActiveSupport::Concern 来防止模块被包括多次调用的回调结果.请参阅下面的示例:

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)

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