按多列分组，然后投影

Question

在下面的代码中，我试图从原始序列返回一个按 ProductName、Size 和 Packaging 属性分组的新序列类型，但我得到了一个未分组的新类型序列。我在这里错过了什么？

query{
        for row in allDeliveries do
        let key = AnonymousObject<_,_,_>(row.ProductName,row.Size,row.Packaging)
        groupValBy row key into g
        select g
    }
    |> Seq.map (fun (del) -> 
    {
        POFD = del;
        ProductName = del.Key.Item1;
        Size = del.Key.Item2;
        Packaging = del.Key.Item3;
        Quantity = del.Count()
    })

Answer 1

这是我的解决方案：

query{
        for row in allDeliveries do
        groupValBy row (row.ProductName, row.Size, row.Packaging) into g
        select {
            POFD = g;
            ProductName = query{
                for row2 in g do
                select row2.ProductName
                headOrDefault
            }

            Size = query{
                for row2 in g do
                select row2.Size
                headOrDefault
            }
            Packaging = query{
                for row2 in g do
                select row2.Packaging
                headOrDefault
            }
            Quantity = g.Count()
        }
    }