Hi,

I'm writing a facebook style messaging system for a Rails App and I'm having trouble selecting the Messages for the inbox (with will_paginate).

The messages are organized in threads, in the inbox the most recent message of a thread will appear with a link to it's thread. The thread is organized via a parent_id 1-n relationship with itself.

So far I'm using something like this:

class Message < ActiveRecord::Base
  belongs_to :sender, :class_name => 'User', :foreign_key => "sender_id"
  belongs_to :recipient, :class_name => 'User', :foreign_key => "recipient_id"
  has_many :children, :class_name => "Message", :foreign_key => "parent_id"
  belongs_to :thread, :class_name => "Message", :foreign_key => "parent_id"
end

class MessagesController < ApplicationController

  def inbox
    @messages = current_user.received_messages.paginate :page => params[:page], :per_page => 10, :order => "created_at DESC"
  end
end

That gives me all the messages, but for one thread the thread itself and the most recent message will appear (and not only the most recent message). I can also not use the GROUP BY clause, because for the thread itself (the parent so to say) the parent_id = nil of course.

Anyone got an idea on how to solve this in an elegant way? I already thought about adding the parent_id to the parent itself and then group by parent_id, but I'm not sure if that works.

Thanks