public static function getLast() {
		
		$class = get_called_class();

		// check about single primary key
		if ($class::hasCompoundKey()) {
			return NULL;
		}
		
		// check if auto-increment key
		$db = Database::getInstance();
		if (!$db->isAutoIncrement($class::TABLE_NAME)) {
			return NULL;
		}
		
		// cast to string
		$tableKey = (is_array($class::TABLE_KEY) and array_key_exists(0, $class::TABLE_KEY)) ? $class::TABLE_KEY[0] : $class::TABLE_KEY;

		$db->setQuery('SELECT * FROM `' . $class::TABLE_NAME . '` ORDER BY `' . $tableKey . '` DESC LIMIT 1');
		$obj = $db->loadObject();

		return (is_a($obj, 'stdClass') ? new $class($obj) : NULL);
		
	}