groupby multiple columns in a F# 3.0 query

Question

Just trying out F# 3.0 and hit a bit of a wall when it comes to grouping by multiple columns. The obvious thing to try was

query {
    for d in context.table         


        

Answer 1

//in F# 3.0
open Microsoft.FSharp.Linq.RuntimeHelpers
open Microsoft.FSharp.Linq.RuntimeHelpers.LeafExpressionConverter
open System.Linq

//[<CLIMutable>]
//type MyRecord = { Column1 : int; Column2 : int }
// require constructor in F#
// groupBy is not valid

type T(column1 : int, column2 : int)
    member val Colum1=colum1 with get,set
    membre val Colum2=colum2 with get,set

query {
    for d in context.table do
    groupValBy d (NewAnonymousObjectHelper(T(d.Colum1,d.Colume2))) into g
    select (g.Key)
    }

Answer 2

When using groupBy you need to select an aggregating function (e.g. count, sum, avg...).