public static function getWrapper($link)
 {
     if (empty(self::$wrapper)) {
         self::$wrapper = new DAOWrapper($link);
     }
     return self::$wrapper;
 }
 protected function __construct($link, $tablepre)
 {
     $this->wrapper = DAOWrapper::getWrapper($link);
     $this->tablepre = $tablepre;
 }