core/DB.php
public static function engine()
    {
        if (self::$engine != null) {
            return self::$engine;
        }
        $driver = Config::get('db.db_driver', 'Mysql');
        if ($driver == 'Mysql') {
            self::$engine = Mysql::instance();
            return self::$engine;
        }
        throw new \Exception('不支持的数据库驱动类型');
    }
public static function engine()
    {
        if (self::$engine != null) {
            return self::$engine;
        }
        $driver = Config::get('db.db_driver', 'Mysql');
        if ($driver == 'Mysql') {
            self::$engine = Mysql::instance();
            return self::$engine;
        }
        throw new \Exception('不支持的数据库驱动类型');
    }
获取数据库引擎实例
@return Mysql|null
@throws MysqlException