[英]linq refactoring (possibly using nested group by clause)
我已经写了一些linq,但是我对此不满意。 我想将两个linq语句(可能带有嵌套的group by子句?)重构为一个子句。
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)));
}
涉及的实体有:
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; }
}
成员具有许多结果和许多分类(但每个分类年仅一个分类)。
我需要生成特定年份(例如2013)的结果列表,按日期排序。 需要根据分类类别的Value属性对结果进行分组,然后按结果类别的Value属性对结果进行排序。
作为一棵树,结果集/层次结构可能看起来像这样:
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)
但是最终,我真正想要的只是结果对象的平面列表:
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)
第一个linq语句最初按日期对数据进行分组,然后ResultList包含该日期的所有结果。
然后,循环中的第二个linq语句处理每个ResultList,按分类对数据进行分组(忽略某些分类)并对这些结果进行排序,最后获得前3个结果。
循环还具有(我认为是)可怕的.ToList(ForEach(.ToList(.ForEach())))lambda表达式,可以将层次结构展平为结果对象列表。
因此,尽管这确实有效,但它非常可怕。 如何合并两个linq语句并替换lambda表达式以使结果变平?
好的,所以我想出的最后一个linq是这个,包括最后的SelectMany可以拼凑成一个列表:
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();
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