gistfile1.rb

module Rankable
  extend ActiveSupport::Concern

  included do
    field :ratings_value_sum, :type => Integer, :default => 0
    field :ratings_count, :type => Integer, :default => 0
    embeds_many :ratings

  end

  module InstanceMethods
    def rating; ratings_value_sum || 0; end
    def rated?(user)
      user && self.ratings.any?{|r| r.user_id == user.id}
    end
    def can_rate?(user)
      if !user
        false
      elsif self.respond_to?(:user) && self.user == user
        false
      elsif rated?(user)
        false
      else
        true
      end
    end
    def rate(user, value = 1)
      rating = Rating.new(:value => value)
      rating.user = user

      rating_params = {
        '_id' => self.id,
        'ratings' => {'$not' => {'$elemMatch' => {'user_id' => user.id}}}
      }
      rating_attrs = {
        '$push' => 
          {'ratings' => rating.raw_attributes},
        '$inc' => 
          {'ratings_value_sum' => value, 'ratings_count' => 1}
      }

      result = self.class.collection.update(rating_params, rating_attrs, :safe => true, :muti => false)

      result[0][0]['updatedExisting']
    end
  end
end


class Rating
  include Mongoid::Document

  field :value, :type => Integer
  field :created_at, :type => Time, :default => Time.now

  embedded_in :rankable, :inverse_of => :ratings
  belongs_to_related :user
end