Bitrix Framework

Events

You can use standard ORM mechanisms to subscribe to iblock entity events:

use Bitrix\Main\ORM\Data\DataManager;
		
// iblock ID
$iblockId = 32;

// iblock object
$iblock = \Bitrix\Iblock\Iblock::wakeUp($iblockId);

// event manager
$em = \Bitrix\Main\ORM\EventManager::getInstance();

$em->registerEventHandler(
    $iblock->getEntityDataClass(),
    DataManager::EVENT_ON_BEFORE_ADD,
    'mymodule',
    'MyClass',
    'method'
);

Custom property types

You need to set an individual callback GetORMFields to add your own fields to entity when describing the property:

public static function GetUserTypeDescription()
{
    return [
        ...
        "GetORMFields" => array(__CLASS__, "GetORMFields"),
    ];
}

/**
 * @param \Bitrix\Main\ORM\Entity $valueEntity
 * @param \Bitrix\Iblock\Property $property
 */
public static function GetORMFields($valueEntity, $property)
{
    $valueEntity->addField(
        ...
    );
}