protected function update( $key, $value ) {

		$columns = static::table()->get_columns();

		$data = array(
			$key => $columns[ $key ]->prepare_for_storage( $value )
		);

		$res = static::make_query_object()->update( $this->get_pk(), $data );

		if ( $res && static::$_cache ) {
			Cache::update( $this );
		}

		return $res;
	}