c# - 如何从 linq 查询中检索聚合值？

Question

我有以下查询：

from spl in SpeciesLists 
         join ar in Areas on spl.Station.Area equals ar.Id 
         join ground  in Grounds on ar.Ground equals ground.Id 
         join re in Regions on ground.Region  equals re.Id 
         where spl.Station.Trip.year ==2013
         select new 
           {
              SpciesCommonName = slp.Description,
              Are = ar.description,
              Ground = ground.Code,
              NumberOfTripsInProtectedAreas = "To be calculated",
           }

“行程”可以包括一个或多个站点。保护区字段位于 Trip 表中，可以是 1 或 0。一个站点有一个或多个物种。

如何计算保护区的出行次数？

提前谢谢了

Answer 1

您需要在 where 子句中添加 ProtectedArea == 1 的条件。

同样如您的评论中所述，该组将由：slp.Description、ar.description 和 ground.Code

这是代码：

from spl in SpeciesLists 
             join ar in Areas on spl.Station.Area equals ar.Id 
             join ground  in Grounds on ar.Ground equals ground.Id 
             join re in Regions on ground.Region  equals re.Id 
             where spl.Station.Trip.year ==2013
             && spl.Station.Trip.ProtectedArea == 1
             group spl by new { slp.Description, ar.description, ground.Code } into Result
             select new 
               {
                  SpciesCommonName = Result.Key.Description,
                  Are = Result.Key.description,
                  Ground = Result.Key.Code,
                  NumberOfTripsInProtectedAreas = Result.Count()
               }