code: protected function _fetchOne($id)
      {
  
          /** @var ActiveRecord $model */
          $model = $this->query->andWhere([$this->tableName. '.id' => $id])->one();
  
          if (!$model)
              throw new NotFoundHttpException(Yii::t('wavecms/main', 'Element not found'));
  
          if ($this->controller->scenario) {
              $model->scenario = $this->controller->scenario;
          }
  
          return $model;
      }
docs: Function to get one model by id. Using in crete/update/page action
  @param $id
  @return ActiveRecord
  @throws \yii\web\NotFoundHttpException
  @throws InvalidConfigException