Question

我有两个列表

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 }
};

需要输出

StoreName =商店1 | TotalValue = 38.24

~~LINQ to SQL~~ LINQ to Objects

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();

错误：当前上下文中不存在名称“o”。

在这种情况下，如何按顺序过滤？

Answer 1

试试这个：

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)
              });

或者这个

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)
              });

请注意，通常无需调用ToList，因为这需要立即评估查询。大多数情况下，将其保留为IEnumerable<T>就足够了。此外，这还将为“商店2”返回一行TotalValue = 0。如果你也想省略这些行，你可以使用这样的东西。

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 
              });

或者这个

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 
              });

LINQ - Group Join + Where子句

1 个答案: