public function actionDeleteAll()
 {
     $passModel = new ChangePasswordForm();
     if (Yii::app()->request->isPostRequest) {
         $pass = $_POST["pass"];
         $model = new Examen();
         if ($passModel->isPasswordCorrect($pass)) {
             $model->deleteAll();
             echo "true";
         } else {
             echo "false";
         }
         // we only allow deletion via POST request
     } else {
         throw new CHttpException(400, 'Solicitud de página inválida.');
     }
 }