为has_many或habtm动态创建after_add和after_remove回调？ [英] Dynamically create after_add and after_remove callbacks for has_many or habtm?

问题描述

有没有办法动态添加 after_add 和 after_remove 回调到现有的 has_many c

Is there a way to dynamically add after_add and after_remove callbacks to an existing has_many or has_and_belongs_to_many relationship?

例如，假设我有模型 User ， Thing 和一个连接模型 UserThingRelationship $ c> User 模型是这样的：

For example, suppose I have models User, Thing, and a join model UserThingRelationship, and the User model is something like this:

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

我想能够在一个扩展的模块中用户，添加：after_add 和：after_remove User.has_many（：things，...）关系。 Ie，有类似

I'd like to be able to, in a module that extends User, add :after_add and :after_remove callbacks to the User.has_many(:things, ...) relationship. I.e., have something like

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

这样

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

实际上与

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，回调被扩展的模型，因为 ActiveRecord :: Base＃after_save 只是一个类方法。

This can be done pretty effectively for adding after_save, etc, callbacks to the model that's being extended, since ActiveRecord::Base#after_save is just a class method.

推荐答案

我能够通过使用 ActiveRecord :: Reflection ：

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，所以如果有人能想出在未来几天更好的解决方案。

I don't want to answer my own question, so I won't give myself answer credit if someone else can come up with a better solution in the next few days.

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