Multipe relationships in Rails where the class name does not match the association name

Question

I have a private message model that relates to two users, how do I setup an association so that PM.sender is the sender's user model and PM.receiver is recipient's user model? (so that I can call PM.sender.username etc.)

I have a sender_id and receiver_id field.

Answer 1

Assuming model classes Message and User, in your Message model:

class Message < ActiveRecord::Base
  belongs_to :sender, :class_name => 'User'
  belongs_to :receiver, :class_name => 'User'
end

Because the class name can't be deduced from the association name the explicit :class_name is required.

Update: Having just checked, the :foreign_key parameter shouldn't be required as long as the name of the foreign key is the name of the association followed by _id, which it is in this case.