递归-实现省市区三级联动

public static function linkage()
{
    //由于数据量太大，只循环了pid=1的数据 (查询省市区的id，区域名称,父级id)
    $data = Address::whereIn('type',[2,3,4])->get(['id','name','pid'])->toArray();
    return self::getTree($data);
}
//递归
public static function getTree($data,$pid =1)
{
    $list = [];
    foreach ($data as $value)
    {
        //第一次遍历，找到父节点为1的
        if ($value['pid'] == $pid){
            //开始递归，查找父id为该节点id的节点
            if (!empty(self::getTree($data, $value['id']))){
                $value['childList'] = self::getTree($data, $value['id']);
            }
            $list[] = $value;
        }
    }
    return $list;