Question

假设我有一张包含运送历史记录的表格。我想编写一个查询来计算每个用户的发货量，并从该表中该用户的最新条目中获取发货名称。

表结构简单： ShipmentID 会员ID ShippingName ShippingDate

如何编写LINQ C＃查询来执行此操作？

Answer 1

听起来可能想要这样的东西：

var query = from shipment in context.ShippingHistory
            group shipment by shipment.MemberID into g
            select new { Count = g.Count(),
                     MemberID = g.Key,
                     MostRecentName = g.OrderByDescending(x => x.ShipmentDate)
                                       .First()
                                       .ShipmentName };

Answer 2

不是真正的LINQ答案，但个人，我会为此而放弃SQL，以确保它没有做任何N + 1等;例如：

select s1.MemberID, COUNT(1) as [Count],
    (select top 1 ShippingName from Shipping s2 where s2.MemberID = s1.MemberID
     order by s2.ShippingDate desc) as [LastShippingName]
from Shipping s1
group by s1.MemberID

你可能会做类似（未经测试）的LINQ：

var qry = from row in data
          group row by row.MemberId into grp
          select new {
               MemberId = grp.Key,
               Count = grp.Count(),
               LastShippingName =
              grp.OrderByDescending(x => x.ShippingDate).First().ShippingName
           };

LINQ：按聚合分组，但仍然从最近一行获取信息？

2 个答案: