Using variables in Shopify Function Query

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Imagine you're developing a Shopify application, and you encounter a scenario where you need to dynamically fetch cart line attributes in discount functions. This common challenge often requires a deeper understanding of how to pass dynamic variables within Shopify functions. In this guide, we'll explore a step-by-step approach to achieving this goal, making your Shopify development process more efficient and flexible.

Assign Metafield

To begin, let's assign a metafield, which we can later retrieve in our GraphQL query. During the registration of our function, we'll include the necessary metafield information. For instance, let's consider creating a discount function using the CreateAutomaticDiscount mutation.

mutation CreateAutomaticDiscount($discount: DiscountAutomaticAppInput!) {
    discountCreate: discountAutomaticAppCreate(automaticAppDiscount: $discount) {
        userErrors {

Here, we'll pass variables to the query, including the base discount properties and the dynamically assigned metafield:

discount: {
            metafields: [
                namespace: "$app:namespace",
                key: "cartAttribute",
                type: "json",
                value: JSON.stringify({
                  cartLineKey: "myKey"

Now, with the metafield assigned, we're ready to access it in our GraphQL query.

Configure .toml

Next, let's update the shopify.extension.toml file to include variable information. This step is crucial for specifying the namespace and key of the metafield created for our function.

namespace = "$app:namespace"
key = "cartAttribute"

Replace the placeholders with your specific namespace and key values. This configuration enables us to access the metafield in our GraphQL query.

Writing GraphQL query

With the metafield configured, we can now construct our GraphQL query to dynamically fetch cart line attributes. Here's an example query:

query RunInput($cartLineKey: String) {
  cart {
    lines {
      attribute: attribute(key: $cartLineKey) {
      merchandise {
        ... on ProductVariant {
          product {

In this query, we utilize the dynamically assigned cartLineKey parameter to fetch the cart line attribute specified in the metafield. This approach offers flexibility and scalability in accessing dynamic variables within Shopify functions.


By following these steps, you can effectively pass dynamic variables within Shopify functions, enhancing the functionality and customization options of your applications. Whether you're building discount functions or other features, leveraging metafields and GraphQL queries allows for seamless integration of dynamic data. Implement these strategies in your Shopify development workflow to streamline processes and create more dynamic and personalized user experiences.