store itemList in session

i have the follwong database structure

catgegory (CatId,CatType,CatName)
Product(ProductId,ProductName,CatId)
Service(ServiceId,ServiceName,CarId)

in the category Table (CatType is either product or services store as "P" OR "S")

im using SortedList to store session of product or service

my problem im using productId as Key in the sortedList however there might be situation where ServiceId and productId as identically i would like to get some adivce how i can redesign or improve this code thank you

code

Private Sub AddToCart(ByVal CartItem As CartItem)

Dim Cart As SortedList = GetCart()
 Dim k As Integer = objTempCart.ProductId
 If Cart.ContainsKey(k) Then
            CartItem = CType(Cart(k), CartItem)
            CartItem.objProduct.OrderQty = CartItem.objProduct.OrderQty + 1
            CartItem.objProduct.Total = CartItem.objProduct.OrderQty * CartItem.objProduct.ProductPrice
        Else
            Cart.Add(k, CartItem)
            CartItem.objProduct.OrderQty = 1
            CartItem.objProd开发者_如何学Cuct.Total = CartItem.objProduct.OrderQty * CartItem.objProduct.ProductPrice

  End Sub

    Private Function GetCart() As SortedList

        If Session("Cart") Is Nothing Then
            Session.Add("Cart", New SortedList)
        End If
        Return CType(Session("Cart"), SortedList)
    End Function

You could concat the CatType and the ID to get a unique string as key for the SortedList(f.e. "P4711" and "S12345").

But normally i would use two SortedList, one for every category. That makes the code less error-prone and more legible.