linq重構（可能使用嵌套的group by子句）

Question

我已經寫了一些linq，但是我對此不滿意。 我想將兩個linq語句（可能帶有嵌套的group by子句？）重構為一個子句。

var queryDB = from res in Results
        where res.SeasonYear == 2013
            group res by res.resultDate into g
            orderby g.Key
            select new 
            {
                ResultDate = g.Key
                , ResultList = g.OrderByDescending(r => r.Value)
            };

List<result> finalList = new List<result>();

foreach (var list in queryDB.Select(k=>k.ResultList).ToList())
{
    var query5 = from item in list
        where item.member.classifications.First(c => c.ClassificationYear == 2013).Value != "U"
        group item by item.member.classifications.First(c => c.ClassificationYear == ClassificationYear).Value into g
        orderby g.Key
        select g.ToList().OrderByDescending(r => r.Value).Take(3);

        query5.ToList().ForEach(c => c.ToList().ForEach(r => finalList.Add(r)));

}

涉及的實體有：

public class Member
{    
    public string Surname { get; set; }
    public virtual ICollection<Result> Results { get; set; }
    public virtual ICollection<Classification> Classifications { get; set; }
}
public class Result
{
    public int Value { get; set; }
    public int SeasonYear { get; set; }
    public Member member { get; set; }
}
public class Classification
{
    public string Value { get; set; }
    public int ClassificationYear { get; set; }
    public Member member { get; set; }
}

成員具有許多結果和許多分類（但每個分類年僅一個分類）。

我需要生成特定年份（例如2013）的結果列表，按日期排序。 需要根據分類類別的Value屬性對結果進行分組，然后按結果類別的Value屬性對結果進行排序。

作為一棵樹，結果集/層次結構可能看起來像這樣：

13/04/2013
    classification.Value = A
        Result (Result.Value = 44)
        Result (Result.Value = 41)
        Result (Result.Value = 40)
    classification.Value = B
        Result (Result.Value = 42)
        Result (Result.Value = 39)
        Result (Result.Value = 36)
    classification.Value = C
        Result (Result.Value = 37)
        Result (Result.Value = 35)
        Result (Result.Value = 34)      

11/05/2013
    classification.Value = A
        Result (Result.Value = 40)
        Result (Result.Value = 39)
        Result (Result.Value = 38)
    classification.Value = B
        Result (Result.Value = 39)
        Result (Result.Value = 38)
        Result (Result.Value = 37)
    classification.Value = C
        Result (Result.Value = 38)
        Result (Result.Value = 36)
        Result (Result.Value = 35)  

但是最終，我真正想要的只是結果對象的平面列表：

Result (.Value= 44,.Date= 13/04/2013,.Member.Classification.Value for 2013= A)
Result (.Value= 41,.Date= 13/04/2013,.Member.Classification.Value for 2013= A)
Result (.Value= 40,.Date= 13/04/2013,.Member.Classification.Value for 2013= A)
Result (.Value= 42,.Date= 13/04/2013,.Member.Classification.Value for 2013= B)
Result (.Value= 39,.Date= 13/04/2013,.Member.Classification.Value for 2013= B)
Result (.Value= 36,.Date= 13/04/2013,.Member.Classification.Value for 2013= B)
Result (.Value= 37,.Date= 13/04/2013,.Member.Classification.Value for 2013= C)
Result (.Value= 35,.Date= 13/04/2013,.Member.Classification.Value for 2013= C)
Result (.Value= 34,.Date= 13/04/2013,.Member.Classification.Value for 2013= C)
Result (.Value= 40,.Date= 11/05/2013,.Member.Classification.Value for 2013= A)
Result (.Value= 39,.Date= 11/05/2013,.Member.Classification.Value for 2013= A)
Result (.Value= 38,.Date= 11/05/2013,.Member.Classification.Value for 2013= A)
Result (.Value= 39,.Date= 11/05/2013,.Member.Classification.Value for 2013= B)
Result (.Value= 38,.Date= 11/05/2013,.Member.Classification.Value for 2013= B)
Result (.Value= 37,.Date= 11/05/2013,.Member.Classification.Value for 2013= B)
Result (.Value= 38,.Date= 11/05/2013,.Member.Classification.Value for 2013= C)
Result (.Value= 36,.Date= 11/05/2013,.Member.Classification.Value for 2013= C)
Result (.Value= 35,.Date= 11/05/2013,.Member.Classification.Value for 2013= C)

第一個linq語句最初按日期對數據進行分組，然后ResultList包含該日期的所有結果。

然后，循環中的第二個linq語句處理每個ResultList，按分類對數據進行分組（忽略某些分類）並對這些結果進行排序，最后獲得前3個結果。

循環還具有（我認為是）可怕的.ToList（ForEach（.ToList（.ForEach（））））lambda表達式，可以將層次結構展平為結果對象列表。

因此，盡管這確實有效，但它非常可怕。 如何合並兩個linq語句並替換lambda表達式以使結果變平？

Answer 1

好的，所以我想出的最后一個linq是這個，包括最后的SelectMany可以拼湊成一個列表：

var filteredResults = 
   from res in Results
   where res.SeasonYear == 2013
   orderby res.resultDate
   group res by res.resultDate into dateGroup
   select new
   {
      ResultDate = dateGroup.Key,
      ResultList =
         from r in dateGroup
         where r.member.classifications.Single(c => c.year == 2013).Value != "U"
         group r by r.member.classifications.Single(c => c.year == 2013).Value into classifications
         orderby classifications
         select new
         {
            ClassificationGroup = classifications.Key,
            ClassificationList =                                     
               from r2 in classifications.OrderByDescending(r => r.Value).Take(3)
               select r2
         }          
   };       

   finalList = filteredResults.SelectMany(item => item.ResultList)
                              .SelectMany(inner=>inner.ClassificationList)
                              .ToList();