acts_as_commentable for ActiveRecord

acts_as_commentable.rb

# ActsAsCommentable
module Commentable #:nodoc:

  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def acts_as_commentable
      has_many :comments, :as => :commentable, :dependent => :destroy, :order => 'created_at ASC'
      include Commentable::InstanceMethods
      extend Commentable::SingletonMethods
    end
  end

  # This module contains class methods
  module SingletonMethods

    # Helper method to lookup for comments for a given object.
    # This method is equivalent to obj.comments.
    def find_comments_for(obj)
      commentable = ActiveRecord::Base.send(:class_name_of_active_record_descendant, self).to_s

      Comment.find(:all,
        :conditions => ["commentable_id = ? and commentable_type = ?", obj.id, commentable],
        :order => "created_at DESC")
    end

    # Helper class method to lookup comments for
    # the mixin commentable type written by a given user.
    # This method is NOT equivalent to Comment.find_comments_for_user
    def find_comments_by_user(user)
      commentable = ActiveRecord::Base.send(:class_name_of_active_record_descendant, self).to_s

      Comment.find(:all,
        :conditions => ["user_id = ? and commentable_type = ?", user.id, commentable],
        :order => "created_at DESC")
    end
    
  end

  # This module contains instance methods
  module InstanceMethods
    
    # Helper method to sort comments by date
    def comments_ordered_by_submitted
      Comment.find(:all,
        :conditions => ["commentable_id = ? and commentable_type = ?", id, self.type.name],
        :order => "created_at DESC")
    end

    # Helper method that defaults the submitted time.
    def add_comment(comment)
      comments << comment
    end
    
  end

end

ActiveRecord::Base.send :include, Commentable # install it in-place