code: public function actionUpdate($id)
      {
          $model = $this->findModel($id);
          
  		$model->tags = !empty($model->tags)?explode(",",$model->tags):[];
  		
  		$post = Yii::$app->request->post();
  		if (isset($post['Banner']['tags']))
  		{
  			if (is_array($post['Banner']['tags']))
  			{
  				$post['Banner']['tags'] = implode(",",$post['Banner']['tags']);
  			}	
  		}
  		
  		$transaction = Yii::$app->db->beginTransaction();
  		try {				
  			if ($model->load($post) && $model->save()) {
  				$model->updatePosition($model->position);
  				$transaction->commit();
  				return $this->redirect(['view', 'id' => $model->id]);
  			}					
  			else
  			{
  				$transaction->rollBack();	
  			}
  		} catch (Exception $e) {
  			$transaction->rollBack();
  		}
  		        
  		return $this->render('update', [
  			'model' => $model,
  		]);
  	
      }
docs: Updates an existing Banner model.
  If update is successful, the browser will be redirected to the 'view' page.
  @param integer $id
  @return mixed