src/Model.php
static function Db() : Connection {
        if (!isset(self::$_connection)) {
            [$host, $port, $user, $password, $db_name, $charset] = self::$_config;
            self::$_connection = new Connection($host, $port, $user, $password, $db_name, $charset);
        }
        return self::$_connection;
    }
static function Db() : Connection {
        if (!isset(self::$_connection)) {
            [$host, $port, $user, $password, $db_name, $charset] = self::$_config;
            self::$_connection = new Connection($host, $port, $user, $password, $db_name, $charset);
        }
        return self::$_connection;
    }
获取当前实例的数据库连接

@return Connection