yii\rbac\DbManager::getRolesByUser PHP Method

    public function getRolesByUser($userId)
    {
        if (!isset($userId) || $userId === '') {
            return [];
        }
        $query = (new Query())->select('b.*')->from(['a' => $this->assignmentTable, 'b' => $this->itemTable])->where('{{a}}.[[item_name]]={{b}}.[[name]]')->andWhere(['a.user_id' => (string) $userId])->andWhere(['b.type' => Item::TYPE_ROLE]);
        $roles = [];
        foreach ($query->all($this->db) as $row) {
            $roles[$row['name']] = $this->populateItem($row);
        }
        return $roles;
    }

 /**
  * when user login in backend , it should be 'Administrator' or ,'Merchant'
  */
 public static function beforeLogin()
 {
     Event::on(\yii\web\User::className(), \yii\web\User::EVENT_BEFORE_LOGIN, function ($event) {
         $user = $event->identity;
         $auth = new DbManager();
         $auth->init();
         $role = $auth->getRolesByUser($user->id);
         $event->isValid = in_array(current($role)->name, ['Administrator', 'Merchant']);
     });
 }