Linq To DataTalbe 列X不属于表

项目中遇到一个问题，利用linq to datatable查询得到一个query,截止到红色代码部分时，一切都正常，只要一运行query.where 就会报异常：列“SingDate”不属于列表，查看了半天都不知道是为什么，下面是原来的代码：

    var query = from r in deptName.AsEnumerable()
                             select new
                             {
                                 BizDept = r.Field<string>("DEP_NAME"),
                                 BizDeptNO = r.Field<string>("DEP_NO"),
                                 TotalNum = (from item in dt.AsEnumerable()
                                             where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                             select item).ToList().Count(),
                                 TotalNumEnd = (from item in dt.AsEnumerable()
                                                where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                && item.Field<DateTime>("SingDate").ToString("yyyy-MM") == temEnd
                                                select item).ToList().Count(),
                                 TotalMainAmount = (from item in dt.AsEnumerable()
                                                    where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                    && item.Field<string>("MainID") == null
                                                    select new { tm = item.Field<decimal>("Amount") }).Sum(p => p.tm) * Convert.ToDecimal(0.00001),
                                 TotalMainAmountEnd = (from item in dt.AsEnumerable()
                                                       where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                       && item.Field<string>("MainID") == null && item.Field<DateTime>("SingDate").ToString("yyyy-MM") == temEnd
                                                       select new { tm = item.Field<decimal>("Amount") }).Sum(p => p.tm) * Convert.ToDecimal(0.00001),
                                 TotalSubAmount = (from item in dt.AsEnumerable()
                                                   where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                   && item.Field<string>("MainID") != null
                                                   select new { tm = item.Field<decimal>("Amount") }).Sum(p => p.tm) * Convert.ToDecimal(0.00001),
                                 TotalSubAmountEnd = (from item in dt.AsEnumerable()
                                                      where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                      && item.Field<string>("MainID") != null && item.Field<DateTime>("SingDate").ToString("yyyy-MM") == temEnd
                                                      select new { tm = item.Field<decimal>("Amount") }).Sum(p => p.tm) * Convert.ToDecimal(0.00001),
                                 TotalAmount = (from item in dt.AsEnumerable()
                                                where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                select new { tm = item.Field<decimal>("Amount") }).Sum(p => p.tm) * Convert.ToDecimal(0.00001),
                                 TotalAmountEnd = (from item in dt.AsEnumerable()
                                                   where item.Field<string>("BizDeptNO") == r.Field<string>("DEP_NO")
                                                   && item.Field<DateTime>("SingDate").ToString("yyyy-MM") == temEnd
                                                   select new { tm = item.Field<decimal>("Amount") }).Sum(p => p.tm) * Convert.ToDecimal(0.00001)
                             };
   var tem = query.ToList();
                 dt = DataTableHelper.ToDataTable(tem);
                 if (string.IsNullOrWhiteSpace(dept))
                 {
                     DataRow dr = dt.NewRow();
                     dr["BizDept"] = "合计";
                     dr["BizDeptNO"] = "";
                     dr["TotalNum"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalNum);
                     dr["TotalNumEnd"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalNumEnd);
                     dr["TotalMainAmount"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalMainAmount);
                     dr["TotalMainAmountEnd"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalMainAmountEnd);
                     dr["TotalSubAmount"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalSubAmount);
                     dr["TotalSubAmountEnd"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalSubAmountEnd);
                     dr["TotalAmount"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalAmount);
                     dr["TotalAmountEnd"] = query.Where(p => p.BizDeptNO != "").Sum(p => p.TotalAmountEnd);
                     dt.Rows.InsertAt(dr, dt.Rows.Count - );
                 }

最终，用query.ToList()代替类query，再进行计算，这个错误才消失，即：query.ToList().Where(……）！也就是像下面这样修改代码

   var tem = query.ToList();
                 dt = DataTableHelper.ToDataTable(tem);
                 if (string.IsNullOrWhiteSpace(dept))
                 {
                     DataRow dr = dt.NewRow();
                     dr["BizDept"] = "合计";
                     dr["BizDeptNO"] = "";
                     dr["TotalNum"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalNum);
                     dr["TotalNumEnd"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalNumEnd);
                     dr["TotalMainAmount"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalMainAmount);
                     dr["TotalMainAmountEnd"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalMainAmountEnd);
                     dr["TotalSubAmount"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalSubAmount);
                     dr["TotalSubAmountEnd"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalSubAmountEnd);
                     dr["TotalAmount"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalAmount);
                     dr["TotalAmountEnd"] = tem.Where(p => p.BizDeptNO != "").Sum(p => p.TotalAmountEnd);
                     dt.Rows.InsertAt(dr, dt.Rows.Count - );
                 }

难道说，直接再次调用query.Where，之前的查询（var query=……）,还会默认执行一次么？

为了验证，我把SingDate字段设置成常量，再次运行，果然又报异常了，这次是其他的列不属于表，还真是，再次调用query.where, 原来的查询还会默认执行一遍！但问题又来了，就算再执行一遍，我的数据源不应该一直有数据么，怎么会找不到列了呢？难道数据源也改变了？这个问题，暂时记下，有时间继续研究研究。

如果哪位大哥知道原因，一定告诉小弟，先谢谢了！