c# - 在 Master 中对记录进行分组，但希望对 Details 进行计数

Question

请考虑以下表格：

掌握：

Id              Year               Season                 Flag           City
------------------------------------------------------------------------------
1               2020                 1                    8000           Paris
2               2020                 1                    7000           Paris
3               2020                 1                    9000           London
4               2020                 2                    3000           Tokyo
5               2020                 2                    1000           Paris
6               2020                 3                    2000           Tokyo 
7               2020                 1                    1000           London
8               2019                 4                    8000           Paris
9               2019                 4                    2000           Paris

细节：

 Id              MasterId                Year            Season             CurrentFlag
--------------------------------------------------------------------------------------
 1                   8                   2020              1                    8000   
 2                   9                   2020              1                    2500  
 3                   8                   2020              2                    8100
 4                   1                   2020              2                    8000
 5                   2                   2020              2                    7500
 6                   2                   2020              3                    7500
 7                   3                   2020              2                    6000
 8                   4                   2020              3                    5000
 9                   7                   2020              2                    4000

考虑Master作为我的记录生命周期的开始并在季节Details中显示。CurrentFlag现在我想要一个Linq为以下结果带来此结果的查询(Year == 2010 and Season == 1)：

City      (Count Master All)  (Count Master Flag<8000) (Count Details All)  (Count Details Current Flag<8000)
--------------------------------------------------------------------------------------------------------- 
Paris          2                       1                     2                    1
London         1                       1                     0                    0 

我写了这个查询：

var Records = (from m in master
                    join d in details
                       on m.Id equals d.MasterId into outerJoin
                    from d in outerJoin
                    where (m.Year == year && m.Dore == dore) ||
                          (d.Year == year && d.Dore == dore)
                     group m by new { m.City } into grp            <--------
                     select new
                     {
                            City = grp.Key.City,
                            Count_Master_All = grp.Count(),
                            Count_Master_Below_8000 = grp.Where(o => o.Flag < 8000),
                            Count_Details_All = ???
                            Count_Details_Below_8000 = ???                                       
                      }).ToList();

第一个问题是我只能对记录进行分组m，因此我无法计算详细表的期望记录。我怎么能做到这一点？

谢谢

标签： c#entity-frameworklinqlambdalinq-to-entities

Answer 1

稍后在查询中执行 Group

var Records = (from m in master
               join d in details
                 on m.Id equals d.MasterId into outerJoin
               from d in outerJoin
               where (m.Year == year && m.Dore == dore) ||
                     (d.Year == year && d.Dore == dore)
               select new {m = m, d = d})
               .GroupBy(x => new { x.m.City })
               .Select(grp => new
               {
                  City = grp.Key.City,
                  Count_Master_All = grp.Count(),
                  Count_Master_Below_8000 = grp.Where(o => o.Flag < 8000),
                  Count_Details_All = grp.Count()                                      
               }).ToList();