如何從linq查詢檢索聚合值？

Question

我有以下查詢：

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」字可以包含一個或多個站。保護區字段位於Trip表中，可以是1或0.一個站有一個或多個物種。

如何計算保護區內的行程次數？

很多感謝

Answer 1

您需要添加ProtectedArea == 1的條件下你的where子句。

而且在你的評論指出，該集團將是：slp.Description，ar.description和 ground.Code

下面是代碼：

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() 
       }