QueryHelper::prepareFolderTreeQuery

static function prepareFolderTreeQuery($parentId): string
{
	$subQuery = new Query(ObjectPathTable::getEntity());
	$subQuery
		->registerRuntimeField('folder', [
			'data_type' => DiskInternalsObjectTable::class,
			'reference' => [
				'=this.OBJECT_ID' => 'ref.ID',
			],
			'join_type' => 'INNER',
		])
		->addSelect('OBJECT_ID')
		->addFilter('=folder.TYPE', ObjectTable::TYPE_FOLDER)// type folder
		->addFilter('=folder.ID', new BitrixMainDBSqlExpression('disk_internals_object_path_folder.REAL_OBJECT_ID'))// not link
		->addFilter('=PARENT_ID', $parentId)
	;

	return $subQuery->getQuery();
}