## notifications_controller.rb

class NotificationsController < ApplicationController

  def create
    notification = Notification.create :user_id => current_user.id, :discussion_id => params[:discussion_id],
                        :discussion_type => params[:discussion_type]
    @discussion = notification.discussion
    render :partial => 'form'
  end

  def destroy
    notification = Notification.find(params[:id])
    @discussion = notification.discussion
    notification.destroy
    render :partial => 'form'
  end
end

## notificaton.rb

class Notification < ActiveRecord::Base
  belongs_to :user
  belongs_to :discussion, :polymorphic => true
  belongs_to :forum, :class_name => 'Forum', :foreign_key => 'discussion_id'
  belongs_to :topic, :class_name => 'Topic', :foreign_key => 'discussion_id'
end


## _form.rhtml

<% if logged_in? -%>
  Notify on update?
  <% discussion = @discussion if @discussion
     notification = discussion.notifications.find_by_user_id(current_user.id)
     if notification -%>
  Yes | <%= link_to_remote 'No',
              :url => { :controller => 'notifications', :action => 'destroy', :_method => :delete, :id => notification },
              :update => { :success => 'notifications' } %>
  <% else -%>
  <%= link_to_remote 'Yes',
              :url => { :controller => 'notifications', :action => 'create',
                        :discussion_id => discussion.id, :discussion_type => discussion.class },
              :update => { :success => 'notifications' } %> | No
  <% end -%>
<% end -%>


## 031_create_notifications.rb

class CreateNotifications < ActiveRecord::Migration
  def self.up
    create_table :notifications do |t|
      # t.column :name, :string
      t.column :user_id, :integer
      t.column :discussion_id, :integer
      t.column :discussion_type, :string
    end
  end

  def self.down
    drop_table :notifications
  end
end


## notification_test.rb

require File.dirname(__FILE__) + '/../test_helper'

class NotificationTest < Test::Unit::TestCase
  all_fixtures

  def test_create_user_watching_forum
    rails = forums(:rails)
    rails.observers<<users(:sam)
    assert_equal 1, Notification.count
  end

  def test_create_user_watching_topic
    sticky = topics(:sticky)
    sticky.observers<<users(:sam)
    assert_equal 1, Notification.count
  end

  def test_remove_user_watching_forum
    test_create_user_watching_forum
    rails = Forum.find(forums(:rails).id)
    rails.notifications.find_by_user_id(users(:sam).id).destroy
    assert_equal 0, Notification.count
  end

  def test_remove_user_watching_topic
    test_create_user_watching_topic
    sticky = Topic.find(topics(:sticky).id)
    sticky.notifications.find_by_user_id(users(:sam).id).destroy
    assert_equal 0, Notification.count
  end

end