id_for_database

# File activerecord/lib/active_record/attribute_methods/primary_key.rb, line 83
      def id_for_database # :nodoc:
        if self.class.composite_primary_key?
          @primary_key.map { |col| @attributes[col].value_for_database }
        else
          @attributes[@primary_key].value_for_database
        end
      end