First create a method in common under application. Here we take the department data table department as an example.

The database table structure is as follows:

1. Find the following sub-departments and output them in tree form. The code in common is:

   function GetMenuID($pid){
   $list = \think\Db::table("department")
   ->where("pid",$pid)
   -->select();
   return $list;
   }
   

2. #The code in the controller is:

   $list = Db::table('bumen')->where('pid',0)->select();//Find the parent column
   $ this->assign("list",$list);
   return $this->fetch();
   

3. The code in the view is

   <select class="layui-select" name="dpid" id="dpid" required="required" lay-verify="dpid" autocomplete="off">
   {volist name="list" id="vo "}
                                                                                                                                               ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ##" id="po"}
                                                                                                                                                                                                                name="$po['id']|GetMenuID=
   " id="co"}
                                                                                                                                                                                                                    ; |——{$co.dp_name}</option>
   
   
   ##Only three levels are written here. If there are more levels, and so on, the output results are as follows: