具有多态关联的多对多在两个方向上都不起作用

Question

我正在实施使用户能够关注 "followable"（在我的情况下，这些可能是事件、地点或其他用户）的系统。

我的想法：

Follow 模型包含 user_id、可关注类型和 followale_id(加入 table)

class Follow < ActiveRecord::Base
  belongs_to :user
  belongs_to :followable, polymorphic: true
end

事件

class Event < ActiveRecord::Base    
  has_many :follows, as: :followable
  has_many :users, through: :follows
end

地方

class Place < ActiveRecord::Base
  has_many :follows, as: :followable
  has_many :users, through: :follows    
end

用户

class User < ActiveRecord::Base
  has_many :follows
  has_many :events, through: :follows, source: :followable, source_type: "Event"
  has_many :places, through: :follows, source: :followable, source_type: "Place"
  has_many :users, through: :follows, source: :followable, source_type: "User"
end

问题是现实只在一个方向起作用，我能做到：

user.follows.create(followable:event1) #follow event1
user.follows.create(followable:place1) #follow place1
user.follows.create(followable:user1)  #follow user1
user.follows # displays all following relations user has established

但是，我做不到:

event1.follows #return follow objects(some user - event1 pairs)
event1.users #return all of the users that follow this event
user1.users  #return all of the users that user1 follows, the most confusing part..

以上全部return无。

我应该如何建立关系以使其双向工作？
另外，我想听听一些关于如何改进这个想法的评论，因为这是我第一次玩更复杂的 realtions。提前谢谢你。

Answer 1

让我们从最棘手的用户模型开始：

class User < ActiveRecord::Base
  has_many :follows, source: :user
  has_many :follows_as_fallowable, 
                    class_name: 'Follow',
                    as: :followable

  has_many :followers, through: :follows_as_fallowable,
                       source: :user

  # other users the user is following                     
  has_many :followed_users, through: :follows,
                            source: :followable,
                            source_type: 'User'
end

请注意，我们需要与 follows 的两种不同关系，因为用户可以位于任一列中，具体取决于用户是关注者还是被关注的对象。

我们现在可以做一个简单的测试来检查关系是否设置正确：

joe = User.create(name: 'Joe')
jill = User.create(name: 'Jill')
joe.followers << jill
jill.followed_users.include?(joe) # true
joe.followers.include?(jill) # true

然后设置用户和可关注模型之间的双向关系：

class Event < ActiveRecord::Base
  has_many :follows, as: :followable
  has_many :followers, through: :follows,
                       source: :user
end

class User < ActiveRecord::Base
  # ...
  has_many :followed_events, through: :follows,
                             source: :followable,
                             source_type: 'Event'
end

以下模型（事件）中的关系在每个模型中都几乎相同，因此您可以轻松地将其提取到模块中以供重用：

# app/models/concerns/followable.rb
module Followable
  extend ActiveSupport::Concern

  included do
    has_many :follows, as: :followable
    has_many :followers, through: :follows,
                         source: :user
  end
end

class Event < ActiceRecord::Base
  include Followable
end

class Place < ActiceRecord::Base
  include Followable
end

具有多态关联的多对多在两个方向上都不起作用

Many to many with polymorphic association doesn't work in both directions

polymorphism

ruby-on-rails

has-many-through

polymorphic-associations