如何使用 linq lambda 表达式对内部连接进行分组

Question

我正在尝试将 sql 存储过程转换为 linq。我在使用 groupby 和内部联接时遇到问题。

这是我试过的方法：

var r = _context.Table1
    .GroupBy(x => new { x.OptionId, x.Years, x.Strike })
    .Join(_context.Table2,
        oc => oc.OptionId, o => o.OptionId, (oc, o) => new
        {
            OptionsCosts = oc,
            Options = o
        }).Where(x => x.Options.OptionType == 1
                && x.Options.QualifierId != null
                && x.Options.CreditingMethod != "xxx")
    
    .Select(y => new DataModel.Table1()
    {
        Years = y.Select(a => a.OptionsCosts.Years).FirstOrDefault(),
        Strike = y.Select(a => a.OptionsCosts.Strike).FirstOrDefault(),
        Value = y.Select(a => a.OptionsCosts.Value).FirstOrDefault(),
        ChangeUser = y.Select(a => a.OptionsCosts.ChangeUser).FirstOrDefault(),
        ChangeDate = DateTime.Now,
        OptionId = y.Select(a => a.OptionsCosts.OptionId).FirstOrDefault()
    });

这是我要转换的 SQL：

SELECT o2.OptionId, o2.Years, o2.Strike, SUM(d2.Weights) as 'TotalWeight', COUNT(*) as 'Counts'
FROM Table1 o2
INNER JOIN @Dates d2  --this is a temp table that just holds dates. I was thinking just a where statement could do it???
  ON d2.EffectiveDate = o2.EffectiveDate
INNER JOIN Table2 od2
   ON od2.OptionId = o2.OptionId
  AND od2.OptionType = 1
  AND od2.qualifierid is null
  AND od2.CreditingMethod <> 'xxx' --28095
GROUP BY o2.OptionId,o2.Years, o2.Strike

我的数据有问题所以我确定我做错了什么。

Answer 1

小建议，重写SQL查询时，使用接近SQL的LINQ查询语法更有效避免错误。

var dates = new List<DateTime>() { DateTime.Now }; // fill list

var query = 
    from o2 in _context.Table1
    where dates.Contains(o2.EffectiveDate)
    from od2 in _context.Table1.Where(od2 => // another way to join
         od2.OptionId == o2.OptionId
      && od2.OptionType == 1
      && od2.qualifierid == null
      && od2.CreditingMethod != "xxx")
    group o2 by new { o2.OptionId, o2.Years, o2.Strike } into g
    select new 
    {
       g.Key.OptionId, 
       g.Key.Years, 
       g.Key.Strike, 
       Counts = g.Count()
       // SUM(d2.Weights) as 'TotalWeight', -this one is not available because dates in memory
    };

如果您刚开始并尝试在 LINQ 上重写程序 - EF Core 不是个好主意。 IQueryable 支持太有限，通常你会为每个复杂的 LINQ 查询而战。尝试 linq2db which has temporary tables support and your stored proc can be rewritten into identical LINQ queries. Or you can use linq2db.EntityFrameworkCore 扩展 EF Core 功能。

免责声明。我是这个扩展的创建者，也是 linq2db 的创建者之一。

Answer 2

var table1=_context.Table1
.groupBy(o2=> new{
o2.OptionId
, o2.Years
, o2.Strike
})
.select(s=> new{
s.key.OptionId
, s.key.Years
, s.key.Strike
,TotalWeight=s.sum(x=>x.Weights)
,Counts=o2.count(c=>c.OptionId)
}).tolist();
var result=table1
.Join(_context.Table2,oc => oc.OptionId, o => o.OptionId, (oc, o) => new{ OptionsCosts = oc,  Options = o })
.Where(x => x.Options.OptionType == 1
                && x.Options.QualifierId != null
                && x.Options.CreditingMethod != "xxx")
.select(x=> new {
    x.oc.OptionId,  x.oc.Years,  x.oc.Strike,  x.oc.TotalWeight, x.oc.Counts
}).tolist();

如何使用 linq lambda 表达式对内部连接进行分组

How to groupby with inner join using linq lamba expression

c#

linq

lambda

linq-to-sql

entity-framework-core