Question

正如标题所说，我的目标是在几个列上加入两个表（目标和事务），然后对该连接的结果进行分组，并对来自BOTH表的列的值求和。以下查询仅允许访问join中的FIRST表中的列！

 var actualsVsTargets = (from target in ObjectContext.PipelineTargets
                 join transaction in ObjectContext.Transactions on
                    new
                    {
                        target.Year,
                        target.Quarter,
                        target.StateID,
                        target.ProductGroup.TeamId
                    } equals new
                    {
                        transaction.Year,
                        transaction.Quarter,
                        transaction.StateID,
                        transaction.Product.ProductGroup.TeamId
                    }   
                 where target.Year == year && target.ProductGroup.TeamId == teamId
                 group target by new
                                     {
                                         target.ProductGroupID,
                                         target.StateID,
                                         target.Year
                                     }
                 into targetGroup
                 select new
                            {
                                // this works fine (accessing target column)
                                TargetL1 = targetGroup.Sum(target => target.Level1_Target,
                                // this doesn't work (accessing transaction column)
                                ActualL1 = targetGroup.Sum(trans => trans.Level1_Total)
                            }).SingleOrDefault();

如下所示，在T-SQL中实现这一点很简单，（大致）：

   SELECT
    targets.Year, 
    targets.StateID, 
    SUM(targets.Level1_Target) L1_Target, -- get the sum of targets
    SUM(transactions.Level1_Total) L1_Total -- get the sum of transactions
  FROM PipelineTargets targets 
  JOIN Transactions transactions 
    JOIN Products prods ON 
        transactions.ProductID = prods.ProductID 
    ON 
        targets.Year = transactions.Year and 
        targets.Quarter = transactions.Quarter and 
        targets.StateID = transactions.StateID and 
        prods.ProductGroupID = targets.ProductGroupID
  WHERE targets.Year = '2010' and targets.StateID = 1
  GROUP BY targets.Year, targets.StateID, targets.ProductGroupID

如何在LINQ中执行此操作？

Answer 1

事务变量超出范围。如果将其包含在分组结果中，则可以使用它。

将group by子句改为：

group new
        {
            target,
            transaction
        }
        by new
        {
            target.ProductGroupID,
            target.StateID,
            target.Year
        } into grouped

然后你的select子句可以这样做：

select new
        {
            TargetL1 = grouped.Sum(groupedThing => groupedThing.target.Level1_Target,
            ActualL1 = grouped.Sum(trans => groupedThing.transaction.Level1_Total)
        }).SingleOrDefault();

Answer 2

首先，您应该为相关外键设置导航属性（例如，1：N目标与事务的关系，以及从事务到产品的关系）。如果设置正确，数据库设计/ EF模式应该从您手中完成大部分工作。之后你可以去：

(from target in targets
  where target.Year == year && target.ProductGroup.TeamId == teamId
  group target by new 
                      { 
                        target.ProductGroupID, 
                        target.StateID, 
                        target.Year 
                      } into targetGroup
  select new { Key = targetGroup.Key,
               TargetL1 = targetGroup.Sum(target => target.Level1_Target),
               ActualL1 = targetGroup.SelectMany(tg => tg.Transactions)
                                     .Sum(trans => trans.Level1_Total)
             });

但是，我无法测试它，因此可能存在错误。

LINQ to Entities，连接两个表，然后分组并从两个表中获取列的总和

2 个答案: