单利 pdo 链接数据库

class danli{            public $db;            protected static $ins=null;                protected function __construct(){                                         $servername = "localhost";        $username = "dbname";        $password = "cs.123456789";        try {            $this->db = new PDO("mysql:host=$servername;dbname=kuaijiezou", $username, $password);            //echo "Connected successfully";         }        catch(PDOException $e)        {            echo $e->getMessage();        }                }                public static  function getins(){                    if(self::$ins ==null){                       self::$ins = new self();                    }                    return self::$ins;                }         }        $conn = danli::getins()->db;        

$url = "SELECT id,breakfast,lunch,personal,isdayin FROM my_order";//订单状态已接单   支付状态已支付   订单状态未打印        $res = $conn->query($url)->fetch(PDO::FETCH_ASSOC);        if($res['id']){            $orderid = $res['id'];            $isdayin = $res['isdayin'].$num;            $v='';            if($res['breakfast'] ==34){                $v .= ",breakfast=36";            }            if($res['lunch'] ==34){                $v .= ",lunch=36";            }            if($res['personal'] ==34){                $v .= ",personal=36";            }               $v .= ",status=36";           $sqlup = "UPDATE my_order SET isdayin=$isdayin$v WHERE id=".$res['id'];            $count = $conn->exec($sqlup);