Asp.net mvc 控制器中的ObjectStateManager错误中已存在具有相同密钥的对象

我的控制器中有以下ActionResults（为简单起见，已截断）。当我发布时，我得到了一个错误：ObjectStateManager中已经存在一个具有相同键的对象。我认为这是因为我正在GET ActionResult中加载一个实体：

var t = iEquipmentTaskRepository.GetSingle(taskID);

然后在帖子中再次加载并尝试编辑/保存它。我需要向数据库中添加一个新的维护实体，并更新（现有）EquipmentTask实体中的一个值。如何获取ObjectStateManager中已存在的设备任务的引用？或者，在MaintenanceViewModel中将EquipmentTask实体添加为属性会更好吗？我只想更新EquipmentTask实体中的一个属性/列

// GET
public ActionResult Create(int taskID = 0)
{
    if (taskID == 0)
    {
        return RedirectToAction("SelectEquipmentTask", "Maintenance");
    }
    else
    {
        var t = iEquipmentTaskRepository.GetSingle(taskID);

        var maintenanceViewModel = new MaintenanceViewModel
        {
            DueDate = t.MaintenanceDueDate
        };
        return View(maintenanceViewModel);
    }
}

// POST
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(MaintenanceViewModel maintenanceViewModel)
{
    if (maintenanceViewModel.DueDate != null)
        nextDueDate = maintenanceViewModel.DueDate.AddDays(7);

    Maintenance maintenance = new Maintenance();
    maintenance.RowId = maintenanceViewModel.RowId;

    // this appears to be my problem. I am loading the same EquipmentTask as the GET method does

    var t = iEquipmentTaskRepository.GetSingle(maintenanceViewModel.TaskId);
    EquipmentTask equipmentTask = new EquipmentTask();
    equipmentTask.TaskId = maintenanceViewModel.TaskId;
    equipmentTask.MaintenanceDueDate = nextDueDate;

    try
    {
        if (ModelState.IsValid)
        {
            iMaintenanceyRepository.Add(maintenance);
            iMaintenanceyRepository.Save();

            iEquipmentTaskRepository.Edit(equipmentTask);
            iEquipmentTaskRepository.Save();

            // redirect to the Details view
            return RedirectToAction("Details", "Maintenance", new { id = maintenance.RowId });
        }
    }
    catch (DataException)
    {
        //Log the error (add a variable name after DataException)
        ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
    }
    return View(maintenanceViewModel);
}

---

我知道发生了什么事。我不需要创建EquipmentTask（Duh）的新实例：

var t = iEquipmentTaskRepository.GetSingle(maintenanceViewModel.TaskId);

EquipmentTask equipmentTask = new EquipmentTask(); // <-- this line was not necessary

equipmentTask.TaskId = maintenanceViewModel.TaskId;
equipmentTask.MaintenanceDueDate = nextDueDate;

var equipmentTask = iEquipmentTaskRepository.GetSingle(maintenanceViewModel.TaskId);
equipmentTask.TaskId = maintenanceViewModel.TaskId;
equipmentTask.MaintenanceDueDate = maintenanceViewModel.NextDueDate;