将简单的SQL分组转换为LINQ to SQL

我遇到了麻烦。 我无法理解Stack Overflow上现有的答案，对LINQ to SQL来说太新了，无法自己解决问题。

看到这个SQL：

select p.Name as ProductName, SUM(o.NumberOf) as TotalOrdered from [Order] o join [Product] p on o.ProductId = p.Id group by p.Name 

返回一个漂亮的2列表，其左侧是产品名称，右侧列是已订购产品的总数（所有订单）。 如何在LINQ to SQL中复制它？

这是我到目前为止所得到的：

 var ctx = new DataClasses1DataContext(); var totalProducts = (from o in ctx.Orders join p in ctx.Products on o.ProductId equals p.Id select new { p.Name, o.NumberOf }) .GroupBy(t => t.Name) .Select(g => g.Key, ... ); 

什么在…？

Answer 1

它看起来像你想要的：

 .Select(g => new { ProductName = g.Key, TotalOrdered = g.Sum(x => x.NumberOf) }) 

您可以将整个查询作为单个查询表达式执行，也可以根本不使用查询表达式：

 var totalProducts = ctx.Orders .Join(ctx.Products, o => o.ProductId, p => p.Id, (o, p) => new { p.Name, o.NumberOf }) .GroupBy(t => t.Name, pair => pair.Name, // Key selector pair => pair.NumberOf, // Element selector (key, numbers) => new { ProductName = key, TotalOrdered = numbers.Sum()) }); 

要么：

 var totalProdcuts = from o in ctx.Orders join p in ctx.Products on o.ProductId equals p.Id group o.NumberOf by p.Name into g select new { ProductName = g.Key, TotalOrdered = g.Sum() }; 

Answer 2

 TotalOrdered = g.Sum(o => o.NumberOf) 

使用上面的….比声明可能

  select new { ProductName= g.Key, TotalOrdered = g.Sum(o => o.NumberOf) }; var query = from o in ctx.Orders join p in ctx.Products on o.ProductId equals p.Id group o by new { p.Name, o.NumberOf } into g select new { ProductName= g.Key, TotalOrdered = g.Sum(o => o.NumberOf) }; 

Answer 3

只是粘贴这个，以防有助于知道如何通过GroupJoin方法实现这一点：

 var totalProducts = ctx.Products.GroupJoin(ctx.Orders, outerKeySelProduct => outerKeySelProduct.Id, innerKeySelOrder => innerKeySelOrder.ProductId, (outerKeySelProduct, innerKeySelOrder) => new { ProductName = outerKeySelProduct.Name, TotalOrdered = innerKeySelOrder.Select(n => n.NumberOf).Sum() }); 

如果它可以改进，很高兴它被编辑。