public static function getInstance()
 {
     if (!isset(self::$instance)) {
         $classname = __CLASS__;
         self::$instance = new $classname();
     }
     return self::$instance;
 }
 public function __construct()
 {
     $this->db = iDBConnectionFactory::getInstance();
     $this->error = ErrorCodeHandler::getInstance();
     $base = TRACE_LOG_ROOT;
     if (!defined('TRACE_LOG_ROOT') || !is_writable(TRACE_LOG_ROOT)) {
         $base = '/var/log/';
     }
     $this->dblog = TRACE_LOG_ROOT . '/dbmodel_' . Date("Y") . '.log';
 }