How to add a single gift with purchase using the cart transform API?

Functions
1

I’m trying to build a function so that if a customer adds a product with a specific tag, that will add a free gift to their cart. I’m using the expand operation to add the gift and set it’s price to 0 - this works fine.

expandedCartItems: [
  {
    merchandiseId: line.merchandise.id,
    quantity: 1,
    price: {
      adjustment: {
        fixedPricePerUnit: {
          amount: (line.cost.totalAmount.amount / line.quantity).toFixed(2),
        }
      }
    }
  },
  {
    merchandiseId: FREE_GIFT_VARIANT_ID,
    quantity: 1,
    price: {
      adjustment: {
        fixedPricePerUnit: {
          amount: 0,
        }
      }
    }
  },
]

The issue is, if the customer increases the quantity, the gift also increases. I want to limit the gift to a maximum of 1 in their cart, is this not possible using expand? If so, what is the alternative?

I’m ripping my hair out with 100 tabs open, and a hateful conversation with chat GPT - any help would be much appreciated, thanks!

2

You’ll need to also have a ‘Cart/Checkout validation function’ that ensures the quantity of that cart line is never > 1.

3

@bkspace Ok, does that mean that in order to limit the gift to 1, the qualifying product will also have to be limited to 1? I was kinda hoping the customer could buy 2x main product, and just receive 1x gift. Thank you!

4

It would be possible, but the UX is an open question. Let’s say you determined the cart line to expand via a line attribute. You could use that same line attribute and ensure there’s only 1 in the cart.

Because this all happens at the cart line level, you can definitely add another of the same item, but without the attribute.