c# - LINQ to Sql Left Outer Join 与 Group By 和 Having 子句

Question

我花了一天时间尝试将 sql 查询转换为 LINQ lambda 表达式，但没有成功。

我的 sql 查询:

SELECT a.ID,
       Sum(b.[Value]) AS [Value],
       c.ContractValue
FROM   Contracts a
       LEFT JOIN DepositHistories b
              ON b.ContractID = a.ID
       INNER JOIN LearningPackages c
               ON a.LearningPackageID = c.ID
GROUP  BY a.ID,
          c.ContractValue
HAVING Sum(b.[Value]) < c.ContractValue
        OR Sum(b.[Value]) IS NULL
        OR Sum(b.[Value]) = 0 

这是 LINQ 查询:

var contracts = (
                from a in db.Contracts
                from b in db.LearningPackages.Where(e => e.ID == a.LearningPackageID).DefaultIfEmpty()
                group a by new
                {
                    a.ID,
                    b.ContractValue
                } into g
                from c in db.DepositHistories.Where(e => e.ContractID == g.Key.ID).DefaultIfEmpty()
                where g.Sum(e => c.Value) < g.Key.ContractValue || g.Sum(e => c.Value) == null
                select new
                {
                    ID = g.Key.ID,
                    ContractValue = g.Key.ContractValue,
                    Value = g.Sum(e => c.Value != null ? c.Value : 0)
                }
                ).ToList();

我的结果:

  ID  ContractValue    Value  
  1      6000000      500000  
  1      6000000      500000  
  1      6000000      500000  
  1      6000000      500000  
  1      6000000      500000  
  3      7000000      500000  
  3      7000000      500000  
  3      7000000      500000  
  4      6000000      500000  
  5      6000000      0  
  6      6000000      0 

它不是对值进行分组和求和。

请帮帮我!

谢谢!

Answer 1

你可以这样做:

var result = from b in db.DepositHistories
             join a in db.Contracts on b.CotractID equals a.ID
             join c in db.LearningPackages on a.LearningPackageID equals c.ID
             group b by new{ a.ID,c.COntractValue} into g
             where g.Sum(x=>x.Value) < g.Key.COntractValue 
             || g.Sum(x=>x.Value) == null 
             || g.Sum(x=>x.Value) == 0
            select new 
                  { 
                   ID = g.Key.ID, 
                   Value = g.Sum(x=>x.Value), 
                   ContractValue = g.Key.COntractValue
                  };

我做了一个DEMO FIDDLE更清楚。

更新:

对于左外部连接，您必须将您的条件连接到 somealias 并将它们来自 somealias.DefaultIfEmpty() 中的别名。

这是左外连接的版本，它给出了正确的结果:

var result = from a in Contracts
             join b in DepositHistories on a.ID equals b.CotractID into e
             from f in e.DefaultIfEmpty()
             join c in LearningPackages on a.LearningPackageID equals c.ID
             group f by new 
                       { 
                          a.ID, 
                          c.COntractValue 
                       } into g
             where g.Sum(x => x==null ? 0 : x.Value) < g.Key.COntractValue 
             ||  g.Sum(x => x==null ? 0 : x.Value) == 0
             select new 
                   { 
                      ID = g.Key.ID, 
                      Value = g.Sum(x => x == null ? 0 : x.Value), 
                      ContractValue = g.Key.COntractValue 
                   };

UPDATED FIDDLE DEMO

您还可以检查this SO post about How to do left outer join in LINQ

更新 2:

使用查询方法你必须使用GroupJoin() method用于左外连接。

下面是上面带有方法查询的代码:

var Result = Contracts.GroupJoin(DepositHistories, 
                                    a => a.ID, 
                                    b => b.CotractID, 
                                    (a, b) => new { a = a, b = b })
                                  .Join(LearningPackages, 
                                  a => a.a.LearningPackageID, 
                                  b => b.ID, 
                                  (a, b) => new { a = a, b = b })
                                  .GroupBy(e => new 
                                                    { 
                                                        e.a.a.ID, 
                                                        e.b.COntractValue 
                                                    }, 
                                                    (k, g) => new 
                                                                { 
                                                                    ID = k.ID, 
                                                                    ContractValue = k.COntractValue, 
                                                                    Value =  g.Sum(x => x == null ? 0 : x.a.b.Sum(d=>d.Value)) 
                                                                }
                                            ).Where(x => x.Value < x.ContractValue || x.Value == 0).ToList();

UPDATED FIDDLE WITH METHOD QUERY