public function getPolymorphicRelation()
    {
        if ($this->_cached !== null) {
            return $this->_cached;
        }
        $className = $this->owner->getAttribute($this->classAttribute);
        if ($className == "") {
            return null;
        }
        if (!class_exists($className)) {
            Yii::error("Underlying object class " . $className . " not found!");
            return null;
        }
        $tableName = $className::tableName();
        $object = $className::find()->where([$tableName . '.id' => $this->owner->getAttribute($this->pkAttribute)])->one();
        if ($object !== null && $this->validateUnderlyingObjectType($object)) {
            $this->_cached = $object;
            return $object;
        }
        return null;
    }