yii\db\Connection::beginTransaction PHP Method

    public function beginTransaction($isolationLevel = null)
    {
        $this->open();
        if (($transaction = $this->getTransaction()) === null) {
            $transaction = $this->_transaction = new Transaction(['db' => $this]);
        }
        $transaction->begin($isolationLevel);
        return $transaction;
    }

 /**
  * @throws \yii\base\InvalidConfigException
  * @throws \yii\db\Exception
  */
 public function actionUpdate()
 {
     $assignments = $this->getAllAssignments();
     $useTransaction = $this->authManager instanceof \yii\rbac\DbManager && $this->useTransaction === true;
     $transaction = null;
     if ($useTransaction) {
         $transaction = $this->db->beginTransaction();
     }
     try {
         $this->authManager->removeAll();
         $this->updateRules();
         $this->updateRoles();
         $this->updatePermission();
         $this->updateInheritanceRoles();
         $this->updateInheritancePermissions();
         if (!empty($assignments)) {
             $this->restoreAssignments($assignments);
         }
         if ($transaction !== null) {
             $transaction->commit();
         }
     } catch (\Exception $e) {
         $this->stderr($e->getMessage() . PHP_EOL);
         if ($transaction !== null) {
             $transaction->rollBack();
         }
     }
     if ($this->authManager instanceof \yii\rbac\DbManager) {
         $this->authManager->invalidateCache();
     }
 }