[Solved] Cart/CGCommerce question

[Lostwitheal]

On our site we have a single product, but different buttons to purchase this product contained in the Uploads module. When you click the buy button from an item in the Uploads module the uploadid gets piped into the cart as the SKU. I've already succeeded in altering the way the cart behaves to let me insert a reference number instead of the SKU when you add an item into the cart, however it only records the reference for the first item which goes into the cart and when you try adding another it simply increases the quantity since the product id is the same.

All I need to know is where is the code which decides whether an item is unique (and hence creates a separate entry in the cart) or the same as something already in there (and increases the quantity accordingly)?. Any pointers on how to change the code to get it to do what I want would also be greatly appreciated of course, though once I find it I can likely figure this part out.

Thanks guys.