1. I have just come into contact with TP5, and I am confused about the correlation model in the manual. I am here to ask for help~~ I hope you can get some answers. First post the error screenshot

#2. The model code is as follows

namespace app\index\model;
use think\Model;
class User extends Model{
    public function group(){
        //用户表 belongsToMany 用户组表(关联模型，中间表，关联id1，关联id2)
                return $this->belongsToMany('Group','auth_group_access','uid','group_id');
        }
}

3. The controller code is as follows

namespace app\index\controller;
use think\Controller;
use think\Db;
use think\Request;
use app\index\model\User as Usermodel;

class User extends Controller{
     //用户列表
    public function index(){
        $user = new Usermodel();
        $data = $user->group;
        p($data);die;
        $this->assign('v',$data);
        return $this -> fetch();
    }
｝