PHP致命错误：找不到类mysqli

When I try to connect using mysqli I get the following error below

Fatal error: class panda\mysqli not found and the line is where it says "new mysqli" when it connects

protected $db = null;

public function __construct()
{
    $this->connect();
}

public function connect()
{
    global $config;

    //it errors below here on the "new mysqli"
    $this->db = new mysqli($config['mysqli.host'], $config['mysqli.user'], $config['mysqli.pass'], $config['mysqli.name']);

    if ($this->db->connect_errno) 
    {
        echo 'Failed to connect to MySQLi: (';
        echo $db->connect_errno; 
        echo ') ';
        echo $db->connect_error;
        exit();
    }

    $db->set_charset("utf8");
}

You are working with namespaces and PHP is - by default - trying to resolve mysqli relative from the panda namespace. A general rule is to prepend core-PHP classes with a \ as they reside in the "global space".