Mongoid关系多态关联

Question

有没有人知道如何进行多态关联,Mongoid这是关系优势,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.当我改变referenceto时embed,这一切都按照Mongoid的文档记录,但我需要它reference.

谢谢!

Answer 1

回答古老的帖子,但有人可能会发现它很有用.

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

从 Mongoid Google Group 来看，这似乎不受支持。这是我找到的最新相关帖子。

无论如何，这并不难手动实现。这是我的多态链接，称为“主题”。

实现关系的逆部分可能会更复杂一些，特别是因为您需要跨多个类使用相同的代码。

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