public function actionView($slug)
 {
     $news = News::get($slug);
     if (!$news) {
         throw new \yii\web\NotFoundHttpException('News not found.');
     }
     $news_items = News::last_items(3, $news->model->news_id);
     return $this->render('view', ['news' => $news, 'news_items' => $news_items]);
 }