public function hasVisitor($visitor_id)
    {
        if ($this->visitor !== null) {
            return true;
        }
        /**
         * @var Visitor $model
         */
        $model = Yii::$container->get($this->modelMap['Visitor']['class']);
        $this->visitor = $model->find()
            ->where(['id' => $visitor_id])
            ->one();
        return $this->visitor !== null;
    }