# File lib/mongoid/contexts/mongo.rb, line 224
      def last
        opts = options_with_default_sorting
        opts[:sort] = opts[:sort].map{ |option| [ option[0], option[1].invert ] }.uniq
        attributes = klass.collection.find_one(selector, opts)
        attributes ? Mongoid::Factory.from_db(klass, attributes) : nil
      end