在 Master 中对记录进行分组，但希望对 Details 进行计数

Posted 2023-02-16

【中文标题】在 Master 中对记录进行分组，但希望对 Details 进行计数

【英文标题】：Group records in Master but want count for Details

【发布时间】：2021-09-09 11:25:21

【问题描述】：

请考虑这些表格：

大师：

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

详情：

 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

将Master 视为我的记录生命周期的开始，将Details 视为在季节中显示CurrentFlag。现在我想要一个Linq 查询，为(Year == 2010 and Season == 1) 带来这个结果：

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用m 对记录进行分组，所以我不能计算明细表的期望记录。我该怎么做？

谢谢

【参考方案1】：

稍后在查询中进行分组

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();

【讨论】：

谢谢，但是Count_Details_Below_8000 呢？

会是这样的：Count_Details_All = grp.Where(d => d.CurrentFlag