Yii provides a concept of flash data. Flash data is a session data which −

• Is set in one request.
• Will only be available on the next request.
• Will be automatically deleted afterwards.

Step 1 − Add an actionShowFlash method to the SiteController.

public function actionShowFlash() {
   $session = Yii::$app->session;
   // set a flash message named as "greeting"
   $session->setFlash(''greeting'', ''Hello user!'');
   return $this->render(''showflash'');
}

Step 2 − Inside the views/site folder, create a View file called showflash.php.

<?php
   use yiibootstrapAlert;
   echo Alert::widget([
      ''options'' => [''class'' => ''alert-info''],
      ''body'' => Yii::$app->session->getFlash(''greeting''),
   ]);
?>

Step 3 − When you type http://localhost:8080/index.php?r=site/show-flash in the address bar of the web browser, you will see the following.

Yii also provides the following session classes −

• yiiwebCacheSession − Stores session information in a cache.

• yiiwebDbSession − Stores session information in a database.

• yiimongodbSession − Stores session information in a MongoDB.

• yiiredisSession − Stores session information using redis database.