Prevent duplicate line item. Increment Qty instead

[Greg_L]

Here’s my scenario:

I have three tables: Products, Orders, and Order Details

Now consider this. I’m building out an order, adding line items (order details) to an order. For each line item, I select a Product and quantity and when I click Save the line item gets added to the order.

What I want is to prevent the addition of new order details records where that product was already added. So, if I already added an order detail with product “Apples”, then the next time I try to add another order detail record with the same product I’ve already added (Apples), I want the quantity adjusted/incremented on that record rather than adding the new order detail record.

I would love help with this. I have driven myself mad messing with different combinations of actions and workflows. Thank you!!