private static function connect()
 {
     if (self::$cnt == false) {
         if (!isset($GLOBALS['database_host'])) {
             self::$conn = new MongoClient('localhost');
         } else {
             self::$conn = new MongoClient("mongodb://" . $GLOBALS['database_user'] . ":" . $GLOBALS['database_password'] . "@" . $GLOBALS['database_host']);
         }
         self::$cnt = true;
     } else {
         return false;
     }
 }