public function connectPDO($selectDb = true)
    {
        if (null !== self::$_linkId) {
            return true;
        }
        try {
            self::$_linkId = new PDO(
                'mysql:host=' . $this->_server,
                $this->_user,
                $this->_pass,
                array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES \'UTF8\'')
            );
            self::$_linkId->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            if ($selectDb) {
                self::$_linkId->query('USE ' . $this->_database);
            }
        } catch (PDOException $e) {
            $this->_error = $e->getMessage();
            return false;
        }
        return true;
    }