核心数据提取结果未转换NsManaged子类

Question

    class DeviceModel: NSManagedObject {

            @NSManaged var deviceName: String?;
            @NSManaged var devicePrice: String?;

    }

class DeviceListController: UIViewController {

    var deviceList: [Any] = [];

    override func viewDidLoad() {
        super.viewDidLoad();


    }


    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated);

        let appDelegate: AppDelegate = UIApplication.shared.delegate as! AppDelegate;
        let context = appDelegate.persistentContainer.viewContext;
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Device");

        do {
            self.deviceList =  try context.fetch(request);
        } catch  {
            print(error);
        }
    }
}


extension DeviceListController: UITableViewDataSource, UITableViewDelegate {

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.deviceList.count;
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: DeviceItemCell.reuiseIdentifier) as? DeviceItemCell  else {
            fatalError("Error create tableCell")
        }

        guard let item = deviceList[indexPath.row] as? DeviceModel else {
            fatalError("Item not convertable DeviceModel");
        }

        cell.deviceName.text = item.value(forKey: "devicePrice") as! String

        return cell;

    }
}

  

让item = deviceList [indexPath.row]作为？ NSManagedObject是工作，但   当我将NSManagedObject更改为DeviceModel类保护返回时   错误为什么我不将项目转换为DeviceModel类？但是DeviceModel   类是子类NsManagedObject