protected static function addGuest($ip, $url)
    {
        $activity = static::find()->where(['ip' => $ip, 'user_id' => null])->limit(1)->one();
        if (empty($activity)) {
            $activity = new static;
            $activity->ip = $ip;
        }
        $activity->url = $url;
        return $activity->save();
    }