c# - LINQ 查询到 Group 并获得 Sum

Question

我有以下查询，它加入了由 StationId 加入的 RailwayStation 对象和 ExpenditureData 对象的集合，我正在尝试获取前 10 个 StationCargoCodes(Station 对象的一个​​属性)，并选择顶部的 ExpenditureCost 的总和10 但我无法获得正确的语法:

var data = (from s in stations join e in expenditureData on s.stationId 
equals e.StationId 
orderby e.expenditureAmount descending 
select s)
.Sum(e => e.expenditureAmount)
.GroupBy(n => n.StationCargoCode)
.Take(10);

为此，我需要什么 LINQ 来进行分组和求和？

Answer 1

var query = from s in stations
            join e in expenditureData
                on s.stationId equals e.StationId into se
            group se by new
            {
                s.StationCargoCode, ExpenditureCostSum = se.Sum(x => x.ExpenditureCost)
            } into g
            orderby g.Key.ExpenditureCostSum descending
            select g.Key;

var top10 = query.Take(10).ToList();