Rails 4 +

Question

有没有人知道如何在Mongoid中进行多态关联，这种关联有利于关系，而不是嵌入关联。

例如，这是我的Assignment模型：

class Assignment
  include Mongoid::Document
  include Mongoid::Timestamps

  field :user
  field :due_at, :type => Time

  referenced_in :assignable, :inverse_of => :assignment
end

可以与多个模型建立多态关系：

class Project
  include Mongoid::Document
  include Mongoid::Timestamps

  field :name, :type => String

  references_many :assignments
end

这会抛出一个错误，指出未知的常量Assignable。当我将reference更改为embed时，这一切都按照Mongoid's documentation中的说明进行操作，但我需要reference。

谢谢！

Answer 1

回答古老的帖子，但有人可能觉得它很有用。

现在还有一个多态belongs_to：

class Action                                                                                                                           
  include Mongoid::Document                                                                                                            
  include Mongoid::Timestamps::Created                                                                                                 

  field :action, type: Symbol

  belongs_to :subject, :polymorphic => true                                                                                            
end

class User                                                                                                                             
  include Mongoid::Document                                                                                                            
  include Mongoid::Timestamps                                                                                                          
  field :username, type: String
  has_many :actions, :as => :subject   
end

class Company                                                                                                                          
  include Mongoid::Document                                                                                                            
  include Mongoid::Timestamps                                                                                                          

  field :name, type: String                                                                                                            

  has_many :actions, :as => :subject
end

Answer 2

来自Mongoid Google Group似乎不支持此功能。这是我找到的newest relevant post。

无论如何，这并不难以手动实现。这是我的多态链接，名为Subject。

实现关系的反向部分可能会稍微复杂一些，尤其是因为跨多个类需要相同的代码。

class Notification
  include Mongoid::Document
  include Mongoid::Timestamps

  field :type, :type => String
  field :subject_type, :type => String
  field :subject_id, :type => BSON::ObjectId

  referenced_in :sender, :class_name => "User", :inverse_of => :sent_notifications
  referenced_in :recipient, :class_name => "User", :inverse_of => :received_notifications

  def subject
    @subject ||= if subject_type && subject_id
      subject_type.constantize.find(subject_id)
    end
  end

  def subject=(subject)
    self.subject_type = subject.class.name
    self.subject_id   = subject.id
  end
end

Answer 3

Rails 4 +

以下是如何在 Mongoid 中为Comment模型实现多态关联，该模型可以同时属于Post和Event模型。

Comment模型：

class Comment
  include Mongoid::Document
  belongs_to :commentable, polymorphic: true

  # ...
end

Post / Event模特：

class Post
  include Mongoid::Document
  has_many :comments, as: :commentable

  # ...
end

使用疑虑：

在Rails 4+中，您可以使用Concern模式并在commentable中创建一个名为app/models/concerns的新模块：

module Commentable
  extend ActiveSupport::Concern

  included do
    has_many :comments, as: :commentable
  end
end

并且模型中只有include这个模块：

class Post
  include Mongoid::Document
  include Commentable

  # ...
end

Mongoid关系多态关联

3 个答案:

Rails 4 +