public static function primary_key()
	{
		$id_only = static::get_primary_key_id_only_status();
		$pk_status = static::get_primary_key_status();

		if ($id_only)
		{
			return static::getNonTimestampPks();
		}

		if ($pk_status && ! $id_only)
		{
			return static::$_primary_key;
		}

		return array();
	}