不正确的结果,我做错什么了?

我有以下简单的LINQ to SQL语句:

string strUserID = Eval("whoInsert").ToString();

insLusHmoobDataContext userDataContext = new insLusHmoobDataContext();

var userName = from usr in userDataContext.Users
               where usr.UserId.Equals(strUserID)       
               select usr.UserName;

return userName.ToString();

而不是给我看 UserName 从 aspnet_Users 表中,它显示了SQL select语句。知道吗?