GroupBy Linq IEnumerable 错误

Question

我正在尝试对 IEnumerable 进行分组。但是，每当我尝试完成时，我都会不断收到错误消息。

Dim query As IEnumerable(Of CreditItem) = _
    From credits In unprocessedCredits _
    Group credits By unprocessedCreditsGrouped = _
           New With {Key .Make = credits.Make, _ 
                     Key .Part = credits.PartNumber, _
                     Key .CustomerNumber = credits.CustomerNumber, _ 
                     Key .OrderNumber = credits.OrderNumber} _
    Into Group _
                    Select New CreditItem With { _
                    .Make = unprocessedCreditsGrouped.Make, _
                    .Part = unprocessedCreditsGrouped.PartNumber, _
                    .CustomerNumber = unprocessedCreditsGrouped.CustomerNumber, _
                    .OrderNumber = unprocessedCreditsGrouped.OrderNumber _
                    })

我需要按多个属性分组，例如按品牌、零件编号、客户编号。 unprocessedCredits 还包含字段“数量”，我需要根据 group by 子句获取数量的总和。选择新 CreditItem 不起作用。获取一些未为指定参数指定的参数。

但是，我不知道我是否真的需要 select 语句，因为我真的想选择这个 ienumerable 中的所有内容。

不只是这些属性，但我认为 group by 不可能？

Answer 1

您可以直接创建CreditItem 作为分组变量：

Dim query As IEnumerable(Of CreditItem) = _
    From credits In unprocessedCredits _
    Group credits By unprocessedCreditsGrouped = _
           New CreditItem With _
                         { _
                             .Make = credits.Make, _ 
                             .Part = credits.PartNumber, _
                             .CustomerNumber = credits.CustomerNumber, _ 
                             .OrderNumber = credits.OrderNumber _
                         } _
    Into Group _
    Select unprocessedCreditsGrouped