dbSet.Attach(good);
var stateEntry = ((IObjectContextAdapter)context).ObjectContext.
ObjectStateManager.GetObjectStateEntry(good);
stateEntry.SetModified();
stateEntry.SetModifiedProperty("Title");
stateEntry.SetModifiedProperty("UpdateDate");
context.SaveChanges();
如果出现
对一个或多个实体的验证失败。有关详细信息，请参见“EntityValidationErrors”属性 还需在SaveChanges前先关闭验证实体有效性（ValidateOnSaveEnabled）这个开关 最终代码
dbSet.Attach(good);
var stateEntry = ((IObjectContextAdapter)context).ObjectContext.
ObjectStateManager.GetObjectStateEntry(good);
stateEntry.SetModified();
stateEntry.SetModifiedProperty("Title");
stateEntry.SetModifiedProperty("UpdateDate");
context.Configuration.ValidateOnSaveEnabled = false;
context.SaveChanges();
context.Configuration.ValidateOnSaveEnabled = true;