C# 使用Linq for Entities lambda在联接表上具有顶部选择的GroupJoin

我有一个具有多->多关系的表，尽管在数据库模式中没有这样分类

我有以下SQL，我想用等效的lambda进行复制

SELECT S1.ServiceId, S1.ServiceDate, S1.TrainNumber, S1.SourceMessageRef, 

S2.SourceMessageRef, S1.Created, S2.Created, S1.vehicles, S1.grossWeight, S1.NettWeight, S1.Tare, S1.Nominal, S2.ConsignmentNoteNum, S2.NumOfWagons, S2.GrossWeight, S2.NettWeight, S2.NominalTonnes
FROM (select c.ServiceId, c.ServiceDate, c.TrainNumber, c.SourceMessageRef, c.Created, COUNT(1) as vehicles, SUM(c.GrossWeight) AS GrossWeight, SUM(c.NettWeight) as NettWeight, sum(c.TareWeight) as Tare, sum(c.NominalWeight) as Nominal
        from [Staging].[Consists] c
        GROUP BY [ServiceId],[ServiceDate],[TrainNumber],[SourceMessageRef],[Created]
        ) AS S1
LEFT OUTER JOIN (SELECT c.Created, c.SourceMessageRef, c.ServiceId, 
                        c.ServiceDate, c.ConsignmentNoteNum, c.GrossWeight, 
                        c.NettWeight, c.NominalTonnes, c.NumOfWagons,
                        row_number() over (partition by c.ServiceId, c.ServiceDate order by c.Created DESC) as rn
                   FROM [Staging].[Consignment] c ) S2 
        ON S2.ServiceId = S1.ServiceId AND S2.ServiceDate = S1.ServiceDate AND S2.rn = 1
ORDER BY S2.ServiceDate DESC, S1.Created DESC, S2.SourceMessageRef DESC, S1.SourceMessageRef DESC

到目前为止，我能做到的最好的事情是：

    var consists = db.Consists
        .GroupBy(c => new { c.ServiceId, c.ServiceDate, c.SourceMessageRef })
        .GroupJoin(db.Consignments,
            a => new { a.Key.ServiceId, a.Key.ServiceDate },
            b => new { b.ServiceId, b.ServiceDate },
            (a, b) => new ConsistOverviewDto() 
                {
                    ServiceId = a.Key.ServiceId,
                    ServiceDate = a.Key.ServiceDate,
                    TrainNumber = a.FirstOrDefault().TrainNumber,
                    ConsistVehicleCount = a.Count(),
                    ConsistGrossWeight = a.Sum(a1 => a1.GrossWeight ?? 0m),
                    ConsistNettWeight = a.Sum(a1 => a1.NettWeight ?? 0m),
                    ConsistTareWeight = a.Sum(a1 => a1.TareWeight ?? 0m),
                    ConsistNominalWeight = a.Sum(a1 => a1.NominalWeight ?? 0),

                    ConsignmentVehicleCount = b.Count(),
                    ConsignmentGrossWeight = b.Sum(b1 => b1.GrossWeight ?? 0m),
                    ConsigmentNettWeight = b.Sum(b1 => b1.NettWeight ?? 0m),
                    ConsignmentNominalWeight = b.Sum(b1 => b1.NominalTonnes ?? 0)
                })
        .OrderByDescending(c => c.ServiceDate);

这似乎不是很接近，尤其是只想匹配第一个外部连接条目（如果有的话）的概念

是否有人可以帮助演示实现与所附SQL类似的功能所需的lambda