属性“LatheNo”是对象的关键信息的一部分，无法修改

Question

您好我正在尝试更新具有多个主键的对象

public class Sublots
{
    public Int64 ID { get; set; }
    public string SubLot { get; set; }
    [ForeignKey("Lathe"), Column(Order = 1)]
    public int LatheNo { get; set; }
    [ForeignKey("Lathe"), Column(Order = 0)]
    public int? LineID { get; set; }

    public virtual Lathe Lathe { get; set; }
}

public class Lathe
{
    [Key, Column(Order = 0)]
    public int LineID { get; set; }
    [Key, Column(Order = 1)]
    public int LatheNo { get; set; }
    public string Name { get; set; }
}

如果我尝试将LatheNo更改为另一个有效的LatheNo：

objSublot.LatheNo = 99;
_dbContext.SaveChanges();

我收到以下错误：

  

System.InvalidOperationException：'属性'LatheNo'是对象密钥信息的一部分，无法修改。 “

我在保存之前尝试将Lathe指定为null，但是我得到了相同的错误

查看型号：

 private Sublots _objSublot;

 public Sublots objSublot
    {
        get { return _objSublot; }
        set { _objSublot = value; RaisePropertyChanged(nameof(objSublot)); }
    }

public PuckViewModel(IPuckDataService dataService, IDialogCoordinator dialogCoordinator)
    {
        _dataService = dataService;
        objSublot = _dataService.GetSublotFromPuckRFID("E004015045D5B5BE"); // To simplify code  
    }

的DataService：

public Sublots GetSublotFromPuckRFID(string strRfid)
    {
        Puck puck = _dbContext.Pucks.Where(p => p.RFID == strRfid).FirstOrDefault();

        if(puck != null && puck.ID > 0)
        {
            return _dbContext.Sublots.Where(s => s.PuckID == puck.ID).OrderByDescending(p => p.ID).FirstOrDefault();
        }
        else
        {
            return null;
        }
    }

 public bool SaveSublot(Sublots objSublot)
    {
        bool answer = false;
        if (objSublot != null)
        {
            objSublot.LatheNo = 13; // Change here to simplify code 
            _dbContext.SaveChanges(); //Error here
            answer = true;
        }
        return answer;
    }