has_one有两个外键？ [英] has_one with two foreign keys?

问题描述

我有两个类Message和User。消息具有sender_id和recipient_id这两个用户的外键。如何建立关系，我将能够获得发件人和收件人的用户，如@ message.sender.name和@ message.recipient.name

我试过这样做：

  class Message< ActiveRecord :: Base 
 
 belongs_to：sender，：class_name => 'User'，：foreign_key => 'sender'
 belongs_to：recipient，：class_name => 'User'，：foreign_key => '收件人'
 
结束
 
类用户< ActiveRecord :: Base 
 
 has_many：recivied_messages，：class_name => 'Message'，：foreign_key => 'recipient'
 has_many：send_messages，：class_name => 'Message'，：foreign_key => 'sender'
 end 
  

但是没有帮助，当我试图访问，例如，@ message.recipient.name它说未定义的方法名称

解决方案

您可以使用：class_name 属性来设置哪个类用于外键：

  class Message< ActiveRecord :: Base 
 has_one：sender，：class_name => User 
 has_one：recipient，：class_name =>用户
结束
 
类用户< ActiveRecord :: Base 
 belongs_to：sent_messages，：class_name =>消息
 belongs_to：received_messages，：class_name =>消息
 end 
  

另外，你说你正在使用 sender_id 和 recipient_id 作为外键，但是在你的代码中你有：foreign_key => 'sender'和：foreign_key => 收件人 。您是否尝试将它们更改为：foreign_key => 'sender_id'和：foreign_key => recipient_id ？所以：

  class Message< ActiveRecord :: Base 
 has_one：sender，：class_name =>用户，：foreign_key => 'sender_id'
 has_one：收件人，：class_name =>用户，：foreign_key => 'recipient_id'
结束
 
 class用户< ActiveRecord :: Base 
 belongs_to：sent_messages，：class_name => Message，＃... etc 
 belongs_to：received_messages，：class_name => Message，＃... etc 
 end 
  

I have two classes Message and User. Message has sender_id and recipient_id both foreign keys for User. How to build relationship where I'll be able to get user for both sender and recipient, like @message.sender.name and @message.recipient.name

I tried to do it by this way:

class Message < ActiveRecord::Base  

  belongs_to :sender, :class_name => 'User', :foreign_key => 'sender'
  belongs_to :recipient, :class_name => 'User', :foreign_key => 'recipient'

end   

class User < ActiveRecord::Base

  has_many :recivied_messages, :class_name => 'Message', :foreign_key => 'recipient'
  has_many :send_messages, :class_name => 'Message', :foreign_key => 'sender'
end

But it didn't help, when I'm trying to access to, for instance, @message.recipient.name it says that "undefined method `name'"

解决方案

You can use the :class_name property to set which class gets used for a foreign key:

class Message < ActiveRecord::Base
  has_one :sender, :class_name => User
  has_one :recipient, :class_name => User
end

class User < ActiveRecord::Base
  belongs_to :sent_messages, :class_name => Message
  belongs_to :received_messages, :class_name => Message
end

Also, you say you are using sender_id and recipient_id for the foreign keys, but in your code you have :foreign_key => 'sender' and :foreign_key => 'recipient'. Have you tried changing them to :foreign_key => 'sender_id' and :foreign_key => 'recipient_id'? So:

class Message < ActiveRecord::Base
  has_one :sender, :class_name => User, :foreign_key => 'sender_id'
  has_one :recipient, :class_name => User, :foreign_key => 'recipient_id'
end

class User < ActiveRecord::Base
  belongs_to :sent_messages, :class_name => Message, # ...etc
  belongs_to :received_messages, :class_name => Message, # ...etc
end

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