Preferred way to private messages modeling in Rails 3

Question

I plan to implement a private message system between members. I'm wondering what are the preferred approaches to this.

Requirements are

1. I should be able to retrieve them easily as something like this

   @user.conversations               #Should return User objects that I sent or received messages from (but not me)
   @user.conversations.messages      #Messages from all or specific user objects.
   @user.conversations.messages.unread      #Unread messages
   

2. When calling @user.conversations should retrieve only the people that sent me messages or people I send messages to. current_user should be excluded.

3. If i'm sender_id=5 and send to_id=10 then, the other person would reply as sender=10 to_id=5. This should be considered and understood as the same conversation object.

---

Regarding last point. I'm not sure what's the preferred approach to modeling.

It's preferred to use one Conversation model to handle all messages such as

    attr_accessible :user_id, :friend_id, :message, :read
    belongs_to :user

Or it's preferred to create a Conversation model to handle association and a Message model for messages.

I would like to see sample cases of how to implement this relationship and if there's additional method to implement.

I'm a bit lost here.

Answer 1

A much simpler model is to capture each Message:

class Message < ActiveRecord::Base
  belongs_to :from_user,  :class_name => 'User' # from_user_id field fk Users
  belongs_to :to_user,    :class_name => 'User' # to_user_id field fk Users
  belongs_to :thread, :class_name => 'Message'  # Reference to parent message
  has_many :replies,  :class_name => 'Message', :foreign_key => 'thread_id'

  named_scope :in_reply_to, lambda { |message| :conditions => {:thread => message}, :order => 'created_at' }
end

class User < ActiveRecord::Base
  has_many :messages_received,  :class_name => 'Message', :foreign_key=> 'to_user_id'
  has_many :messages_sent,      :class_name => 'Message', :foreign_key=> 'from_user_id'
end

If you need to capture the message threads, any Message that's a reply can store a reference to the initial message starting the Conversation (aka Thread). For example:

first_msg   = Message.new(:to_user => bob, :from_user => sally, :body => 'Hello!')
sally_reply = first_msg.replies.build(:to_user => bob, :from_user => sally, :body => 'hi back')
bob_reply   = first_msg.replies.build(:to_user => sally, :from_user => bob, :body => 'later')