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