inCollections(ids: $CollectionIds) always returns empty array in Shopify Discount Function (POS)

Functions
1

Hi Shopify Community,

I’m working on a Shopify Discount Function targeting:

cart.lines.discounts.generate.run

and I’m trying to determine whether a cart line’s product belongs to a specific collection.

GraphQL Input Query

query CartInput($CollectionIds: [ID!]) {
  cart {
    lines {
      merchandise {
        ... on ProductVariant {
          id
          product {
            id
            title
            handle
            collectionIds: inCollections(ids: $CollectionIds) {
              collectionId
              isMember
            }
          }
        }
      }
    }
  }
}

Extension Configuration (shopify.extension.toml)

[extensions.input.variables]
namespace = "$app:discount-bogo"
key = "CollectionIds"

Runtime Input (Logged)

"product": {
  "id": "gid://shopify/Product/11007581258046",
  "title": "Check Blazer",
  "handle": "3905-jacket-in-black",
  "vendor": "PERFORMAX",
  "collectionIds": []
}

Issue

Even though the product is definitely part of the collection,
the response always returns:

"collectionIds": []

No isMember, no collectionId, nothing.

This happens specifically when:

  • The function runs in POS

  • Using cart.lines.discounts.generate.run

  • Passing collection IDs via extensions.input.variables

What I Need

I need a reliable way inside a Discount Function to check whether a product belongs to a collection.

So my questions are:

  1. Is inCollections supported in discount function runtime, especially for POS?

  2. Are extensions.input.variables guaranteed to be available for inCollections?

  3. Is this a known limitation of Shopify Functions where collection membership isn’t resolvable?

  4. If inCollections is not supported, what is the recommended alternative to check product–collection relationships inside a discount function?

Any clarification from Shopify staff or anyone who’s solved this would be appreciated.

Thanks.

FULL INFO
cart_lines_discounts_generate_run.graphql

query CartInput($CollectionIds: [ID!]) {

  cart {

posCheck: attribute(key: "discountlyPos") { value }

lines {

id

cost {

amountPerQuantity {

amount

        }

subtotalAmount {

amount

        }

      }

quantity

merchandise {

... on ProductVariant {

id

product {

id

title

handle

vendor

collectionIds: inCollections(ids: $CollectionIds) {

collectionId

isMember

            }

          }

__typename

        }

      }

    }

  }

discount {

discountClasses

  }

shop {

metafield(key: "DiscountlyBogoDiscountPOS", namespace: "ACPTiered") {

jsonValue

    }

subTotalMeta:metafield(key: "NormalTiers", namespace: "ACPTiered") {

jsonValue

    }

localTime{

date

    }

  }

}

shopify.extension.toml

api_version = “2025-10”

[[extensions]]
name = “t:name”
handle = “discount-function-XXXX”
type = “function”
uid = “4811fdbc-7d6b-0de0-6721-XXXXX”
description = “t:description”

[[extensions.targeting]]
target = “cart.lines.discounts.generate.run”
input_query = “src/cart_lines_discounts_generate_run.graphql”
export = “cart-lines-discounts-generate-run”

[[extensions.targeting]]
target = “cart.delivery-options.discounts.generate.run”
input_query = “src/cart_delivery_options_discounts_generate_run.graphql”
export = “cart-delivery-options-discounts-generate-run”

[extensions.build]
command = “”
path = “dist/function.wasm”

[extensions.input.variables]
namespace = “$app:discount-bogo”
key = “CollectionIds”
2

AND THIS IS THE

**Input (STDIN)
**

      {
  "cart": {
    "posCheck": {
      "value": "2026-01-31T04:57:35,test-chekout002.myshopify.com,81839161662"
    },
    "lines": [
      {
        "id": "gid:\/\/shopify\/CartLine\/0",
        "cost": {
          "amountPerQuantity": {
            "amount": "898.0"
          },
          "subtotalAmount": {
            "amount": "19756.0"
          }
        },
        "quantity": 22,
        "merchandise": {
          "id": "gid:\/\/shopify\/ProductVariant\/49379854188862",
          "product": {
            "id": "gid:\/\/shopify\/Product\/11007581258046",
            "title": "Check Blazer",
            "handle": "3905-jacket-in-black",
            "vendor": "PERFORMAX",
            "collectionIds": []
          },
          "__typename": "ProductVariant"
        }
      }
    ]
  },
  "discount": {
    "discountClasses": [
      "PRODUCT",
      "ORDER"
    ]
  },
  "shop": {
    "metafield": {
      "jsonValue": [
        {
          "MyShopifyDomain": "test-chekout002.myshopify.com",
          "discountTitle": "BOGOO",
          "customerBuys": {
            "buyQuantity": "1",
            "basedOn": "Collection",
            "itemData": [
              {
                "id": "gid:\/\/shopify\/Collection\/470089662782",
                "title": "50% OFF on this items",
                "handle": "50-off-on-this-items",
                "image": "https:\/\/cdn.shopify.com\/s\/files\/1\/0750\/8380\/9086\/collections\/2771165.jpg?v=1713350310"
              }
            ]
          },
          "customerGets": {
            "buyQuantity": "1",
            "basedOn": "Collection",
            "itemData": [
              {
                "id": "gid:\/\/shopify\/Collection\/470089662782",
                "title": "50% OFF on this items",
                "handle": "50-off-on-this-items",
                "image": "https:\/\/cdn.shopify.com\/s\/files\/1\/0750\/8380\/9086\/collections\/2771165.jpg?v=1713350310"
              }
            ]
          },
          "combined": {
            "productCombined": false,
            "orderCombined": false,
            "shippingCombined": false
          },
          "created_date": "2026-01-28T10:33:54.034Z",
          "status": true,
          "startDate": null,
          "endDate": null,
          "discountApplied": "Point_of_Sale",
          "LocationIds": [],
          "location_Obj": null,
          "__v": 0
        }
      ]
    },
    "subTotalMeta": null,
    "localTime": {
      "date": "2026-01-31"
    }
  }
}
3

collectionIds being an empty array suggests that $CollectionIds is not populating correctly. If it was, but the collection membership check was incorrect, you’d still see collectionIds populated, but isMember with a value of false.

The problem likely lies in:

[extensions.input.variables]
namespace = “$app:discount-bogo”
key = “CollectionIds”

Your input.variables metafield should be of type json, and CollectionIds should be a property on the that metafield, of type String[].

You can follow the documentation, which explains how input variables work in functions.

4

Thank you :folded_hands: @bkspace for the clarification and guidance. You were right about the issue being with the input variables configuration. After ensuring the metafield is of type json and confirming CollectionIds is defined correctly as a String[], everything works as expected.

Appreciate the help and the clear explanation.

1 Like
5

No problem! Good luck with your project!

1 Like