c# - EntityFramework.dll 中出现“System.Data.Entity.Infrastructure.DbUpdateException”

Question

我写了一个相当简单的代码(基于 WCF 和 Windows 窗体的客户端服务器)。我试图更新数据库以便测试我的代码，但遇到了上述异常。有什么解决办法吗？

      // For testing 
      public void updateTable() 
      {
        using (var db = new overlayDBEntities())
        {
            var overlaydb = new overlayData
            {
                DeviceId = "1111",
                TimestampUTC = new DateTime(1990, 1, 1, 9, 9, 9),
                OverlayData1 = "Random Text"
            };

            db.overlayData.Add(overlaydb);

            try
            {
                db.SaveChanges();
            }
            catch(Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            var overlaydb1 = new overlayData
            {
                DeviceId = "1111",
                TimestampUTC = new DateTime(2000, 2, 2, 10, 10, 10),
                OverlayData1 = "seconed seconed seconed "
            };

            db.overlayData.Add(overlaydb);

            try
            {
                db.SaveChanges();
            }
            catch (Exception ec) 
            {
                Console.WriteLine(ec.Message);
            }
        }
    }

Answer 1

如果你需要更新数据库中已经存在的行，那么不要使用 context.Add()；你可以按如下方式使用。

    var overlaydb1 = new overlayData
    {
      DeviceId = "1111",
      TimestampUTC = new DateTime(2000, 2, 2, 10, 10, 10),
      OverlayData1 = "seconed seconed seconed "
    };

    try
    {
      db.overlayData.Attach(overlaydb1);
      db.ObjectStateManager.ChangeObjectState(overlaydb1, EntityState.Modified);
      db.SaveChanges();
    }

    catch (Exception ec) 
    {
      Console.WriteLine(ec.Message);
    }