Home/ Questions/Q 3607448
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-18T21:22:37+00:00

I have a Linq Group By query that works. Here’s the query: Dim query

  • 0

I have a Linq Group By query that works. Here’s the query:

        Dim query = From fb As Feedback In lst Where fb.Seller.login_name.ToLower = UserName.ToLower
                    Order By fb.transaction_id Descending, fb.creation Descending _
                    Group fb By fb.transaction_id _
                    Into Group

I don’t like working with anonymous types so I’m trying to delare the result and am hitting an InvalidCastException.

Here’s the type information:

Debug.Print(query.GetType.ToString)

Returns:

System.Linq.GroupedEnumerable`4[Feedback,System.Nullable`1[System.Int32],Feedback,VB$AnonymousType_0`2[System.Nullable`1[System.Int32],System.Collections.Generic.IEnumerable`1[Feedback]]]

and the inner type:

Debug.Print(item.GetType.ToString)

Returns:

VB$AnonymousType_0`2[System.Nullable`1[System.Int32],System.Collections.Generic.IEnumerable`1[Feedback]]

So, armed with this information, here’s the declaration used:

Dim query As IEnumerable(Of IGrouping(Of Int32?, IEnumerable(Of Feedback)))

Here’s the error returned:

Unable to cast object of type 'System.Linq.GroupedEnumerable`4[Feedback,System.Nullable`1[System.Int32],Feedback,VB$AnonymousType_0`2[System.Nullable`1[System.Int32],System.Collections.Generic.IEnumerable`1[Feedback]]]' to type 'System.Collections.Generic.IEnumerable`1[System.Linq.IGrouping`2[System.Nullable`1[System.Int32],System.Collections.Generic.IEnumerable`1[Feedback]]]'.

The Ugly solution is to define an object and step through the results as follows:

Class FeedbackDataItem

    Sub New(ByVal transaction_id As Integer)
        _transaction_id = transaction_id
        _feedbacks = New Feedbacks(Of Feedback)
    End Sub

    Private _transaction_id As Integer
    Public Property transaction_id() As Integer
        Get
            Return _transaction_id
        End Get
        Set(ByVal value As Integer)
            _transaction_id = value
        End Set
    End Property

    Private _feedbacks As Feedbacks(Of Feedback)
    Public Property Feedbacks() As Feedbacks(Of Feedback)
        Get
            Return _feedbacks
        End Get
        Set(ByVal value As Feedbacks(Of Feedback))
            _feedbacks = value
        End Set
    End Property

End Class

And to load up the collection:

    Dim FeedbackData As New List(Of FeedbackDataItem)

    For Each item In query
        Dim fbi As New FeedbackDataItem(item.transaction_id)
        fbi.Feedbacks.AddRange(item.Group)
        FeedbackData.Add(fbi)
    Next

I’m stumped as to the reason why I’m getting this error. It would be nicer to just define the results and retrun them rather that man-handle the data. Am I missing something?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    The result of your query is an IEnumerable(Of anonymous type). If you don’t want it to be anonymous, you need to strongly type it.

    One way is to use the extension method syntax for the group by:

        Dim feedbacks As IEnumerable(Of Feedback) = 
        From fb As Feedback In lst Where fb.Seller.login_name.ToLower = username.ToLower
        Order By fb.transaction_id Descending, fb.creation Descending

    Dim grouped As IEnumerable(Of IGrouping(Of Integer?, Feedback)) = 
         feedbacks.GroupBy(Function(fb) fb.transaction_id)
    • 0