Embedded mongoid referencing - mongodb

Question

My User model has_and_belongs_to_many :conversations.
The Conversation model embeds_many :messages.
The Message model needs to have a sender and a recipient.
I was not able to find referenced_in at the Mongoid documentation.
How do I assign the users in the message? I tried to follow something similar to this implementation, but kept getting BSON::InvalidDocument: Cannot serialize an object of class Mongoid::Relations::Referenced::In into BSON.
November 2013 Update: reference_in no longer works with Mongoid 3.0? Changed to belongs_to and it seems to work the same.

Answer 1

As it turns out, my structure of the Message referencing the User was appropriate, and the serialization error was related to associating the Users with the Conversation. Here is my structure and the creation steps. I appreciate any feedback on better practices, thanks.
class User
include Mongoid::Document
include Mongoid::Timestamps
include Mongoid::Paranoia
has_and_belongs_to_many :conversations
end
class Conversation
include Mongoid::Document
include Mongoid::Timestamps
include Mongoid::Paranoia
has_and_belongs_to_many :users
embeds_many :messages
end
class Message
include Mongoid::Document
include Mongoid::Timestamps
include Mongoid::Paranoia
embedded_in :conversation
embeds_one :sender, class_name: 'User'
embeds_one :recipient, class_name: 'User'
field :content
field :read_at, type: DateTime
field :sender_deleted, type: Boolean, default: false
field :recipient_deleted, type: Boolean, default: false
belongs_to :sender, class_name: "User", inverse_of: :sender, foreign_key: 'sender_id'
belongs_to :recipient, class_name: "User", inverse_of: :recipient, foreign_key: 'recipient_id'
end
Where before I was trying to #conversation.build(user_ids: [#user_one,#user_two]), the appropriate way is to #conversation.users.concat([#user_one,#user_two]). Then you can simply #conversation.messages.build(sender: #user_one, recipient: #user_two).