连接表

Question

使用EntityFramework Core，我想说我有三个表：

Stores
------
StoreId int,
StoreType int,
StoreName varchar(max)

Orders
------
OrderId int,
StoreId int,
TotalCost int,
PaymentType int

OrderItem
---------
ItemId int,
OrderId int,
ItemCost int

让我们说我想要输出以下列：

StoreName  
SumOfTotalWhere(OrderType==1) 
SumOfTotalWhere(OrderType==2) 
SumOfAllOrders
TotalNumOfOrdersForStore
NumberOfAllOrders

有没有办法在没有大量往返的情况下使用EntityFramework Sum / Group机制来实现此输出？我一直无法弄清楚语法。

Answer 1

var answer = (from store in db.stores
             join order in db.orders on store.StoreId equals order.StoreId into subs
             from sub in subs.DefaultIfEmpty()
             group sub by new {store.StoreId, store.StoreName } into gr
             select new 
             {
                 StoreName = gr.Key.StoreName
                 SumOfTotalWhere1 = gr.Where(x => x != null && x.PaymentType == 1).Select(x => x.TotalCost).DefaultIfEmpty().Sum()
                 SumOfTotalWhere2 = gr.Where(x => x != null && x.PaymentType == 2).Select(x => x.TotalCost).DefaultIfEmpty().Sum()
                 SumOfAllOrders = gr.Where(x => x != null).Select(x => x.TotalCost).DefaultIfEmpty().Sum(),
                 TotalNumOfOrdersForStore = gr.Count(x => x != null)
                 NumberOfAllOrders = db.orders.Count()
             }).ToList();