DepartmentRepository::getDirectParentIdsByDepartmentId

public function getDirectParentIdsByDepartmentId($departmentId)
{
	$this->getDepartmentTreeFlat();
	if (!is_array(self::$depTreeFlat))
	{
		return [];
	}

	$res = [];
	foreach (self::$depTreeFlat as $parentDepId => $depIds)
	{
		foreach ($depIds as $nestedDepId)
		{
			if ((int)$nestedDepId === (int)$departmentId)
			{
				$res[] = (int)$parentDepId;
			}
		}
	}
	return array_unique($res);
}