thinkphp-无限分类下根据任意部门获取顶级部门ID

根据所得到的部门编号获取顶级部门ID：

参数 - department_id

表格组织架构:

tab_departments

department_id parent_id name

1　　1　　顶级　　

2　　1 　　第一级

.......

函数:

function getDepartmentId($department_id){
    $departments = M('tab_departments')->getField('department_id,parent_id');

    while($departments[$department_id]>1){
            $department_id = $departments[$department_id];
    }
}

调用方法:

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