public static function setDriver($driver, $env = null)
    {
        $file = realpath(dirname(__FILE__)."/../drivers/$driver.php");
        if (!file_exists($file)) {
            Log::log("ERROR: Driver file $file does not exists");
            return null;
        }
        self::$_driver[self::selectEnvironment($env)] = $driver;
        include_once $file;
    }