How to perform correctly “group by” in linq on DataTable inside vb code?

Question

Why isn\'t the following group by clause working? The original question was how do I perform group in LINQ inside vb code (dot.net v4.0) with DataTable and sum on the group?

Answer 1

In VB.NET, the syntax for grouping by composite keys is comma-separated keys, not an anonymous type:

                 (From e In table
                  Group e By
                    GroupName = e("GroupName"),
                    ProductName = e("ProductName")
                  Into Group
                  Select New With {
                    .ProductName = ProductName,
                    .QTY = Group.Sum(Function(x) Convert.ToInt32(x("QTY"))),
                    .GroupName = GroupName
                 })

With your syntax, it just uses the default equality comparer on the anonymous objects, which doesn't compare the fields.