linq after groupby無法獲得列值

Question

我通過加入從多個表中獲取數據，並且我想將特定列值的數據分組，但是在group by語句後，我可以訪問我的別名及其屬性。我正在犯什麼錯誤？

public List<PatientHistory> GetPatientHistory(long prid) 
{ 
    using(var db = new bc_limsEntities()) 
    { 
     List<PatientHistory> result = 
      (from r in db.dc_tresult 
      join t in db.dc_tp_test on r.testid equals t.TestId into x 
      from t in x.DefaultIfEmpty() 
      join a in db.dc_tp_attributes on r.attributeid equals a.AttributeId into y 
      from a in y.DefaultIfEmpty() 
      where r.prid == prid 
      group new {r,t,a} by new {r.testid} into g 
      select new PatientHistory 
      { 
       resultid = r.resultid, 
       bookingid = r.bookingid, 
       testid = r.testid, 
       prid = r.prid, 
       attributeid = r.attributeid, 
       result = r.result, 
       Test_Name = t.Test_Name, 
       Attribute_Name = a.Attribute_Name, 
       enteredon = r.enteredon, 
       Attribute_Type = a.Attribute_Type 
      }).ToList(); 
     return result; 
    } 
} 

Answer 1

你這樣做是錯誤的。正如Jon在將序列用別名r，t，a分組後所說不存在。分組後，您將收到g的各個元素中的r,t,a的順序g的各個元素。如果你想從每個組中獲得一個對象（例如最近的），你應該試試這個：

List<PatientHistory> result = 
    (from r in db.dc_tresult 
    join t in db.dc_tp_test on r.testid equals t.TestId into x 
    from t in x.DefaultIfEmpty() 
    join a in db.dc_tp_attributes on r.attributeid equals a.AttributeId into y 
    from a in y.DefaultIfEmpty() 
    where r.prid == prid 
    group new {r,t,a} by new {r.testid} into g 
    select new PatientHistory 
    { 
     resultid = g.Select(x => x.r.resultid).Last(), // if you expect single value get it with Single() 
     // .... here add the rest properties 
     Attribute_Type = g.Select(x => x.a.Attribute_Type).Last() 
    }).ToList();