thinkphp-无限分类下根据任意部门获取顶级部门ID

1 function getDepartmentId($department_id){
2     $departments = M(‘tab_departments‘)->getField(‘department_id,parent_id‘);
3 
4     while($departments[$department_id]>1){
5             $department_id = $departments[$department_id];
6     }
7 }

$department_id = session(‘department_id‘);//当前用户的岗位ID
$top_id = getDepartmentId($depatment_id);
dump($top_id);