TYPO3 Core

After I create new domain object, set all properties values, then persist, field where i assigned child domain object doesn't get updated.
Example code:

$userAnswer = $this->objectManager->get(UserAnswer::class);
$question = $this->objectManager->get(QuestionRepository::class)->findByUid(1);

$userAnswer->setQuestion($question);
$userAnswer->setPid($question->getPid());

$this->objectManager->get(PersistenceManager::class)->persistAll();

And my "question" object is not attached to "user answer", field in DB remains to be zero.

In my TCA configuration file "tx_pxasurvey_domain_model_useranswer.php" i have field configuration:

'question' => [
    'exclude' => true,
    'label' => $ll . 'tx_pxasurvey_domain_model_useranswer.question',
    'config' => [
        'type' => 'select',
        'renderType' => 'selectSingle',
        'foreign_table' => 'tx_pxasurvey_domain_model_question',
        'foreign_table_where' => 'AND tx_pxasurvey_domain_model_question.deleted=0',
        'size' => 1,
        'maxitems' => 1
    ],
],

In "ext_tables.sql" "question int(11) unsigned DEFAULT '0'"

In model "UserAnswer.php"

/**
 * question
 *
 * @var \Pixelant\PxaSurvey\Domain\Model\Question
 */
protected $question = null;

After investigation, I find out that this might be caused by "_isDirty()" check in "\TYPO3\CMS\Extbase\Persistence\Generic\Backend" on line "397", where it returns "false".
Does it missing check with property name "$object->_isDirty($propertyName)"?