How to Create Totals Query in LightSwitch?

I did already, and I posted another post with the details ... but I waited so long for answers with no success.

Well, I have tried the following code:

Private Sub Query3_PreprocessQuery(ByRef query As System.Linq.IQueryable(Of LightSwitchApplication.Stock))
query = From n In query _
Group n By n.Order_Date.year, n.Order_Date.month, n.Product_Name Into g=Group _
Select year,month,Product_Name,Quantity = g.sum(Function(n) n.Quantity)
End Sub

My code causes the screen based on Query3 not to load any data...

Please help me, I need to get each product quantites (grouped per month and per product name).

Thanks is advance