LINQ 跨多个表进行聚合

Question

我想在 LINQ to SQL 中复制此查询，但我不太熟悉如何执行此操作。

SELECT A.Recruiter, SUM(O.SaleAmount * I.Commission)  --This sum from fields in two different tables is what I don't know how to replicate
FROM Orders AS O
INNER JOIN Affiliate A ON O.AffiliateID = A.AffiliateID
INNER JOIN Items AS I ON O.ItemID = I.ItemID
GROUP BY A.Recruiter

到目前为止我已经做到了：

from order in ctx.Orders
join item in ctx.Items on order.ItemI == item.ItemID
join affiliate in ctx.Affiliates on order.AffiliateID == affiliate.AffiliateID
group order  //can I only group one table here?
  by affiliate.Recruiter into mygroup
select new { Recruiter = mygroup.Key, Commission = mygroup.Sum(record => record.SaleAmount * ?????) };

Answer 1

group new {order, item} by affiliate.Recruiter into mygroup 
select new {
  Recruiter = mygroup.Key,
  Commission = mygroup
    .Sum(x => x.order.SaleAmount * x.item.Commission)
}; 

以及编写查询的另一种方法：

from aff in ctx.Affiliates
where aff.orders.Any(order => order.Items.Any())
select new {
  Recruiter = aff.Recruiter,
  Commission = (
    from order in aff.orders
    from item in order.Items
    select item.Commission * order.SaleAmount
    ).Sum()
};

Answer 2

试试 linqpad，只需 Google，很棒的工具！