public static function getTable($table_name)
        {
            if (!isset(self::$tables[$table_name])) {
                self::loadNewTable(new $table_name());
            }
            if (!isset(self::$tables[$table_name])) {
                throw new Exception('Table ' . $table_name . ' is not loaded');
            }
            return self::$tables[$table_name];
        }