LINQ - 集團加入+ Where子句

Question

我有兩個列表

var stores = new[] 
{ 
    new { Code = 1, Name = "Store 1" }, 
    new { Code = 2, Name = "Store 2" }  
}; 

var orders = new[] 
{ 
    new { Code = 1, StoreCode = 1, TotalValue = 4.12 }, 
    new { Code = 2, StoreCode = 1, TotalValue = 14.12 }, 
    new { Code = 3, StoreCode = 1, TotalValue = 24.12 } 
}; 

輸出所需

STORENAME =存儲1 |總價值= 38.24

LINQ到SQL LINQ到對象

var result = (from s in stores 
       join o in orders on s.Code equals o.StoreCode into grp 
       where o.TotalValue > 10 // error 
       select new 
       { 
        StoreName = s.Name, 
        TotalValue = grp.Sum(x => x.TotalValue) 
       }).ToList(); 

錯誤： 'O' 不存在於當前上下文存在名稱。

在這種情況下，如何按順序過濾？

Answer 1

試試這個：

var result = (from s in stores 
       join o in orders.Where(x => x.TotalValue > 10) on s.Code equals o.StoreCode into grp 
       select new 
       { 
        StoreName = s.Name, 
        TotalValue = grp.Sum(x => x.TotalValue) 
       }); 

或者這

var result = (from s in stores 
       join o in orders on s.Code equals o.StoreCode into grp 
       select new 
       { 
        StoreName = s.Name, 
        TotalValue = grp.Where(x => x.TotalValue > 10) 
            .Sum(x => x.TotalValue) 
       }); 

注意，它通常沒有必要調用ToList，因爲這需要查詢的立即評估。大多數情況下，將其作爲IEnumerable<T>就足夠了。此外，這也將返回一個'Store 2'的行，TotalValue = 0。如果你想要省略這些行，你可以使用這樣的東西。

var result = (from s in stores 
       join o in orders.Where(x => x.TotalValue > 10) on s.Code equals o.StoreCode into grp 
       let totalValue = grp.Sum(x => x.TotalValue) 
       where totalValue > 0 
       select new 
       { 
        StoreName = s.Name, 
        TotalValue = totalValue 
       }); 

或者這

var result = (from s in stores 
       join o in orders on s.Code equals o.StoreCode into grp 
       let totalValue = grp.Where(x => x.TotalValue > 10) 
            .Sum(x => x.TotalValue) 
       where totalValue > 0 
       select new 
       { 
        StoreName = s.Name, 
        TotalValue = totalValue 
       });