entity framework 5 更新指定字段

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;