Question

我有一个包含多个列的表：HarvestID，HarvestDate，UserID以提及主要的列。对于每个日期，每天将有几个HarvestID。

到目前为止，我有以下linq查询：

TheUserID和TheMonth作为int和DateTime

传入

var MyQuery = from h in MyDC.HarvestTable
              where h.UserID == TheUserID
              where h.HarvestDate.Month == TheMonth.Month
              where h.HarvestDate.Year == TheMonth.Year
              group h by h.HarvestDate.Day into TheDays
              from d in TheDays
              select new
              {
                  TheDay = d.HarvestDate.Date,
                  TheDayCount = (from c in TheDay
                                 select c.HarvestID).Count()
              };

我希望输出是每天的计数列表。查询不会出错，但问题是查询当前没有为每一天返回唯一的行。分组不起作用，我找不到原因。这段代码出了什么问题？

感谢。

Answer 1

var MyQuery = from h in MyDC.HarvestTable
              where h.UserID == TheUserID
              && h.HarvestDate.Month == TheMonth.Month
              && h.HarvestDate.Year == TheMonth.Year
              group h by h.HarvestDate.Day into g
              select new
              {
                  TheDay = g.Key,
                  TheDayCount = g.Count()
              };

在没有数据的日子里，这不会给你零 - 但应该给你一个计数。

http://msdn.microsoft.com/en-us/vcsharp/aa336746是LINQ示例的首页。

Answer 2

它认为您的查询应该是

var MyQuery = from h in MyDC.HarvestTable
              where h.UserID == TheUserID
              where h.HarvestDate.Month == TheMonth.Month
              where h.HarvestDate.Year == TheMonth.Year
              group h by h.HarvestDate.Day into TheDays
              select new
              {
                  TheDay = TheDays.Key,
                  TheDayCount = TheDays.Count()
              };

以上是对上述分组http://msdn.microsoft.com/en-us/vcsharp/aa336754.aspx#simple1

的非常好的参考

linq groupby问题

2 个答案: