think-orm如何动态切换数据库连接

function db($name)
{
    try {
        $con = Db::connect($name);
    } catch (InvalidArgumentException $e) {
        $config = Db::getConfig();
        $config[$name] = [
            //...
        ];
        Db::setConfig($config);
        $con = Db::connect($name);
    }
    return $con;
}