linq to sql的修改报错
try
{
DepotDataContext dataContxt = CommentParameter.DepotContext;
var vardate = from a in dataContxt.S_MessMessageFeedback
where a.DJH == InLnqMess.DJH
select a;
if (vardate.Count() == 1)
{
S_MessMessageFeedback lnqMess = vardate.Single();

lnqMess.SQEvalidateMessage = InLnqMess.SQEvalidateMessage;
lnqMess.SQEYZRY = BasicInfo.UserName;
lnqMess.SQEYZRQ = InLnqMess.SQEYZRQ;
lnqMess.DJZT = "等待质管部确认";
break;

default:
break;
}

dataContxt.SubmitChanges();
}
}
catch (Exception ex)
{
m_err = ex.Message;
return false;
throw;
}
然后报错：无法附加已存在的实体！
才开始学习linq to sql，所以请各位帮忙看一下，是不是还有什么没有写？？

[解决办法]
break;

default:
break;

写这些是什么意思？
[解决办法]

C# code

try  {  DepotDataContext dataContxt = CommentParameter.DepotContext;  var vardate = dataContxt.S_MessMessageFeedback.SingleOrDefault(a=>a.DJH == InLnqMess.DJH);    if vardate !=null)  {        vardate .SQEvalidateMessage = InLnqMess.SQEvalidateMessage;  vardate .SQEYZRY = BasicInfo.UserName;  vardate .SQEYZRQ = InLnqMess.SQEYZRQ;  vardate .DJZT = "等待质管部确认";    dataContxt.SubmitChanges();  }         }  catch (Exception ex)  {  m_err = ex.Message;  return false;  throw;  }
[解决办法]
探讨

try
            {
                DepotDataContext dataContxt = CommentParameter.DepotContext;
                var vardate = from a in dataContxt.S_MessMessageFeedback
                            ……

[解决办法]
用 FirstOrDefault