FileFieldAssembler::getPropertyColumnsIds

private function getPropertyColumnsIds(): array
{
	$result = [];

	$rows = PropertyTable::getList([
		'select' => [
			'ID',
		],
		'filter' => [
			'=IBLOCK_ID' => $this->iblockId,
			'=PROPERTY_TYPE' => PropertyTable::TYPE_FILE,
			'USER_TYPE' => null,
		],
	]);
	foreach ($rows as $row)
	{
		$result[] = ElementPropertyProvider::getColumnIdByPropertyId((int)$row['ID']);
	}

	return $result;
}