_update_record

# File activerecord/lib/active_record/persistence.rb, line 1227
    def _update_record(attribute_names = self.attribute_names)
      attribute_names = attributes_for_update(attribute_names)

      if attribute_names.empty?
        affected_rows = 0
        @_trigger_update_callback = true
      else
        affected_rows = _update_row(attribute_names)
        @_trigger_update_callback = affected_rows == 1
      end

      @previously_new_record = false

      yield(self) if block_given?

      affected_rows
    end