Question

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'”

Answer 1

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