To create a user interface that merchants can use to configure a delivery customization function, use metafields. Metafields provide flexibility to Shopify Functions by storing settings that merchants can manage directly from their Shopify admin.
## What you'll learn
In this tutorial, you'll learn how to do the following tasks:
- Define what configuration settings will be surfaced to merchants.
- Read and use the merchant-defined values in your function.
> Caution:
> In this tutorial, you'll use a metafield namespace that's accessible to any app so that the metafield namespace can be populated using the GraphiQL app. To make your function ready for production, you should update the metafield namespace to use a [reserved prefix](/docs/apps/build/custom-data/ownership#reserved-prefixes) so that other apps can't use your metafield. You'll make this update in [the next tutorial](/docs/apps/checkout/delivery-shipping/delivery-options/ui).
## Requirements
- You've completed the [Getting started with building delivery customizations](/docs/apps/build/checkout/delivery-shipping/delivery-options/build-function) tutorial.
## Step 1: Configure the function
To make your function reusable, you can replace hardcoded values in your function with metafield values. You can update your [input query](/docs/apps/build/functions/input-output/metafields-for-input-queries) to request a metafield value on the created delivery customization, which is the [function owner](/docs/apps/build/functions/input-output/metafields-for-input-queries#how-it-works) for this function API. You can then use that value in your function logic.
1. Navigate to your function in `extensions/delivery-customization`.
```bash
cd extensions/delivery-customization
```
1. Replace the code in the `src/run.graphql` file with the following code.
This update to the input query adds a metafield from the `deliveryCustomization` object, which is the function owner.
The query differs slightly in Rust and JavaScript due to code generation requirements.
```graphql?title: 'Rust input query', filename: 'src/run.graphql'
query Input {
cart {
deliveryGroups {
deliveryAddress {
provinceCode
}
deliveryOptions {
handle
title
}
}
}
deliveryCustomization {
metafield(namespace: "delivery-customization", key: "function-configuration") {
jsonValue
}
}
}
```
```graphql?title: 'JavaScript input query', filename: 'src/run.graphql'
query RunInput {
cart {
deliveryGroups {
deliveryAddress {
provinceCode
}
deliveryOptions {
handle
title
}
}
}
deliveryCustomization {
metafield(namespace: "delivery-customization", key: "function-configuration") {
jsonValue
}
}
}
```
1. If you're using JavaScript, then run the following command to regenerate types based on your input query:
2. If you're using Rust replace the `src/main.rs` file with the following code that will convert the metafield into a data structure in the Rust program.
```rust?title: 'Rust', filename: 'src/main.rs'
use shopify_function::prelude::*;
use std::process;
pub mod run;
#[typegen("schema.graphql")]
mod schema {
#[query("src/run.graphql",
custom_scalar_overrides = {
"Input.deliveryCustomization.metafield.jsonValue" => super::run::Configuration,
}
)]
pub mod run {}
}
fn main() {
eprintln!("Please invoke a named export.");
process::exit(1);
}
```
1. Replace the `src/run.rs` or `src/run.js` file with the following code.
This update includes parsing the JSON metafield value, and using values from that JSON in the function logic instead of hardcoded values.
This change is automatically reflected as long as you're running `dev`.
```rust?title: 'Rust', filename: 'src/run.rs'
use crate::schema;
use shopify_function::prelude::*;
use shopify_function::Result;
#[derive(Deserialize, Default, PartialEq)]
#[shopify_function(rename_all = "camelCase")]
pub struct Configuration {
state_province_code: String,
message: String,
}
#[shopify_function]
fn run(input: schema::run::Input) -> Result {
let no_changes = schema::FunctionRunResult { operations: vec![] };
let config: &Configuration = match input.delivery_customization().metafield() {
Some(metafield) => metafield.json_value(),
None => return Ok(no_changes),
};
let to_rename = input
.cart()
.delivery_groups()
.iter()
.filter(|group| {
if let Some(address) = group.delivery_address() {
address.province_code() == Some(&config.state_province_code)
} else {
false
}
})
.flat_map(|group| group.delivery_options())
.map(|option| schema::RenameOperation {
delivery_option_handle: option.handle().to_string(),
title: match option.title() {
Some(title) => format!("{} - {}", title, config.message),
None => config.message.clone(),
},
})
.map(schema::Operation::Rename)
.collect();
Ok(schema::FunctionRunResult {
operations: to_rename,
})
}
```
```javascript?title: 'JavaScript', filename: 'src/run.js'
// @ts-check
/**
* @typedef {import("../generated/api").RunInput} RunInput
* @typedef {import("../generated/api").FunctionRunResult} FunctionRunResult
* @typedef {import("../generated/api").Operation} Operation
*/
/**
* @type {FunctionRunResult}
*/
const NO_CHANGES = {
operations: [],
};
/**
* @param {RunInput} input
* @returns {FunctionRunResult}
*/
export function run(input) {
// Define a type for your configuration, and parse it from the metafield
/**
* @type {{
* stateProvinceCode: string
* message: number
* }}
*/
const configuration = input?.deliveryCustomization?.metafield?.jsonValue ?? {};
if (!configuration.stateProvinceCode || !configuration.message) {
return NO_CHANGES;
}
let toRename = input.cart.deliveryGroups
.filter(group => group.deliveryAddress?.provinceCode &&
// Use the configured province code instead of a hardcoded value
group.deliveryAddress.provinceCode == configuration.stateProvinceCode)
.flatMap(group => group.deliveryOptions)
.map(option => /** @type {Operation} */({
rename: {
deliveryOptionHandle: option.handle,
// Use the configured message instead of a hardcoded value
title: option.title ? `${option.title} - ${configuration.message}` : configuration.message
}
}));
return {
operations: toRename
};
};
```
## Step 2: Populate the delivery customization configuration metafield
To populate the configuration metafield, you'll first use the [`deliveryCustomizations`](/docs/api/admin-graphql/current/queries/deliveryCustomizations) query to confirm the delivery customization ID, and then use the [`metafieldsSet`](/docs/api/admin-graphql/current/mutations/metafieldsSet) mutation to populate the same metafield that you specified in the input query.
1. Open the [Shopify GraphiQL app](https://shopify-graphiql-app.shopifycloud.com/) on your development store.
1. In the GraphiQL app, in the **API Version** field, select the **2023-07** version.
1. Execute the following query, and make note of the `id` value of the delivery customization that you created in the [previous tutorial](/docs/apps/build/checkout/delivery-shipping/delivery-options/build-function). For more information about global IDs, refer to [Global IDs in Shopify APIs](/docs/api/usage/gids).
```graphql
query {
deliveryCustomizations(first: 100) {
edges {
node {
id
}
}
}
}
```
1. Execute the following mutation and replace `YOUR_CUSTOMIZATION_ID_HERE` with the full global ID of your delivery customization.
The value of the metafield specifies that the function should add a message for the `NC` state/province code. You can adjust this to the state/province of your choice.
```graphql
mutation {
metafieldsSet(metafields: [
{
ownerId: "YOUR_CUSTOMIZATION_ID_HERE"
namespace: "delivery-customization"
key: "function-configuration"
value: "{ \"stateProvinceCode\": \"NC\", \"message\": \"May be delayed due to UFO attack\" }"
type: "json"
}
]) {
metafields {
id
}
userErrors {
message
}
}
}
```
You should receive a GraphQL response that includes the ID of the created metafield. If the response includes any messages under `userErrors`, then review the errors, check that your mutation and `ownerId` are correct, and try the request again.
## Step 3: Test the delivery customization
1. Open your development store, build a cart, and proceed to checkout.
1. Enter a delivery address that doesn't use the specified state/province code. You shouldn't see any additional messaging on the delivery options.
1. Change your shipping address to use your chosen state/province code. Your delivery options should now have the additional messaging.
1. Open your terminal where `shopify app dev` is running, and review your function executions.
When [testing functions on development stores](/docs/apps/build/functions/test-debug-functions#test-your-function-on-a-development-store), the output of `dev` includes executions of your functions, any debug logging you have added to them, and a link to a local file with the full function execution details.
1. In a new terminal window, use the Shopify CLI [`app function replay`](/docs/api/shopify-cli/app/app-function-replay) command to [replay a function execution locally](/docs/apps/build/functions/test-debug-functions#execute-the-function-locally-using-shopify-cli), and debug your function without the need to re-trigger the function execution on Shopify.
1. Select the function execution from the top of the list. Press `q` to quit when you are finished debugging.
## Next steps
- Build a [delivery customization user interface](/docs/apps/build/checkout/delivery-shipping/delivery-options/build-ui) with App Bridge.
- Learn how to use [variables](/docs/apps/build/functions/input-output/use-variables-input-queries) in your input query.