Possible bug in Shopify Function Discount API

[DevAOC]

Hello,

I have run into what I think is a Shopify Cart API bug in Shopify Functions (Product Discount). I am trying to write a function that discounts items depending on a matching zip code and product variant sku. I have noticed that my function works as expected when viewing the cart, however, once I continue to the checkout page my discounts are no longer applied to the cart.

I have noticed a few things here. When I view the logs for the function run while on the cart page, the cart.deliveryGroups has values in the array. Once I navigate to the checkout, the array is empty. This is where I think the bug lies.

My input.graphql code is as follows:
```

query Input {

  cart {

    cost {

      subtotalAmount {

        amount

      }

      totalAmount {

        amount

      }

    }

    deliveryGroups {

      deliveryAddress {

        zip

      }

    }

    lines {

      quantity

      merchandise {

        __typename

        ... on ProductVariant {

          id

          sku

        }

      }

      cost {

        subtotalAmount {

          amount

        }

        totalAmount {

          amount

        }

        amountPerQuantity {

          amount

        }

        compareAtAmountPerQuantity {

          amount

        }

      }

    }

  }

  discountNode {

    metafield(namespace: "postalCodes", key: "codes") {

      value

    }

  }

}

```

My function code is as follows:

```

// @TS-check

import { DiscountApplicationStrategy } from "../generated/api";

/**

* @typedef {import("../generated/api").InputQuery} InputQuery

* @typedef {import("../generated/api").FunctionResult} FunctionResult

* @typedef {import("../generated/api").Target} Target

* @typedef {import("../generated/api").ProductVariant} ProductVariant

*/

/**

* @type {FunctionResult}

*/

const EMPTY_DISCOUNT = {

  discountApplicationStrategy: DiscountApplicationStrategy.Maximum,

  discounts: [],

};

export default /**

* @param {InputQuery} input

* @returns {FunctionResult}

*/

(input) => {

/**

* @type {[{

* code: string

* skuDiscountPairs: {[key: string]: number}

* }]}

*/

const postalCodes = JSON.parse(input?.discountNode?.metafield?.value ?? "{}");

if (!postalCodes) {

  return EMPTY_DISCOUNT;

}

if (!input.cart.deliveryGroups[0]) {

  return EMPTY_DISCOUNT;

}

const cartPostalCode = input.cart.deliveryGroups[0].deliveryAddress?.zip;

let found;

for (const postalCode of postalCodes) {

  if (postalCode.code === cartPostalCode) {

    found = postalCode;

    break;

  }

}

if (!found) {

  return EMPTY_DISCOUNT;

}

const discounts = input.cart.lines

.filter((line) => {

  if (line.merchandise.__typename == "ProductVariant") {

    const variant = /** @type {ProductVariant} */ (line.merchandise);

    if (variant.sku && found.skuDiscountPairs[variant.sku]) {

      return true;

    } else {

      return false;

    }

  }

})

.map((line) => {

  const variant = /** @type {ProductVariant} */ (line.merchandise);

  return {

    targets: [

      {

        productVariant: {

          id: variant.id,

        },

      },

    ],

    value: {

      percentage: {

        // @TS-ignore

        value: found.skuDiscountPairs[variant.sku].toString(),

      },

    },

  };

});

console.log(discounts, "DISCOUNTS");

if (!discounts.length) {

  console.error("No cart lines qualify for volume discount.");

  return EMPTY_DISCOUNT;

}

return {

  discounts,

  discountApplicationStrategy: DiscountApplicationStrategy.Maximum,

  };

};

```

Here is the deliverGroups array and function output while on the cart page:

"deliveryGroups": [      {
        "deliveryAddress": {          "zip": "K4P 0E4"
        }
      }
    ],

{  "discounts": [    {
      "targets": [        {
          "productVariant": {            "id": "gid://shopify/ProductVariant/45022386159917"
          }
        }
      ],
      "value": {        "percentage": {          "value": "10"
        }
      }
    }
  ],
  "discountApplicationStrategy": "MAXIMUM"
}

Here are the deliveryGroups array and output on the checkout page:

"deliveryGroups": [],

{  "discountApplicationStrategy": "MAXIMUM",  "discounts": []}

Please let me know if you have any questions about this bug report.

[ijam]

Hi, I was wondering if you found a solution, because I have a similar issue.

I am calculating my discount based on cart attributes. These attributes are passed just fine to function's Input on cart page. Once I proceed to checkout page, the function is called 3 times, and in the last two calls, attributes on cart are all null, which removes the discount.

I am using the typescript template for product discount 

[DevAOC]

Hey, I have been in contact with support and they have made a ticket to fix
this bug. The delivery groups should definitely be a part of the checkout
page

[Andrew-W]

Did you get a reply about this issue? I'm having a similar thing where I'm trying to create a product discount based on country code but `deliveryGroups` is always empty.

[DevAOC]

I unfortunately have not gotten any information after submitting a bug
report. They said they would look into it but no news yet!

[Andrew-W]

Thanks for the reply! I've submitted a similar post with my issue too. Nearly three months without a reply doesn't look promising though. 😓

[adoshi]

@DevAOC just curious what your postalCodes metafield definition looks like.

[DevAOC]

Its an object with objects in it.