/**
  * Поиск модели
  *
  * @param $id
  * @return array|null|\yii\db\ActiveRecord
  * @throws NotFoundHttpException
  */
 protected function findModel($id)
 {
     $model = Book::findById($id);
     if (!$model) {
         throw new NotFoundHttpException();
     }
     return $model;
 }