动态创建has_many或habtm的after_add和after_remove回调？

Question

有没有办法动态添加after_add和after_remove回调现有的has_many或has_and_belongs_to_many关系？

例如,假设我有模型User,Thing和连接模型UserThingRelationship,User模型是这样的:

class User < ActiveRecord::Base
  has_many :user_thing_relationships
  has_many :things, :through => :user_thing_relationships
end

我希望能够在一个模块中扩展User,添加:after_add和:after_remove回调User.has_many(:things, ...)关系.即,有类似的东西

module DoesAwesomeStuff
  def does_awesome_stuff relationship, callback
    # or however this can be achieved...
    after_add(relationship) callback
    after_remove(relationship) callback
  end
end

以便

class User < ActiveRecord::Base
  has_many :user_thing_relationships
  has_many :things, :through => :user_thing_relationships

  does_awesome_stuff :things, :my_callback
  def my_callback; puts "awesome"; end
end

实际上是一样的

class User < ActiveRecord::Base
  has_many :user_thing_relationships
  has_many :things, :through => :user_thing_relationships, :after_add => :my_callback, :after_remove => :my_callback

  def my_callback; puts "awesome"; end
end

这可以非常有效地添加after_save等等,回调到正在扩展的模型,因为ActiveRecord::Base#after_save它只是一个类方法.

Answer 1

最简单的是

User.after_add_for_things << lambda do |user, thing| 
  Rails.logger.info "#{thing} added to #{user}"
end

Answer 2

我能够通过使用ActiveRecord :: Reflection得到以下内容:

module AfterAdd
  def after_add rel, callback
    a = reflect_on_association(rel)
    send(a.macro, rel, a.options.merge(:after_add => callback))
  end
end

class User < ActiveRecord::Base
  extend AfterAdd

  has_many :user_thing_relationships
  has_many :things, :through => :user_thing_relationships

  after_add :things, :my_callback

  def my_callback
    puts "Hello"
  end
end

我不想回答我自己的问题,所以如果其他人能够在接下来的几天内提出更好的解决方案,我就不会给自己回答.