medusa-store/www/apps/book/app/advanced-development/api-routes/additional-data/page.mdx

import { Details } from "docs-ui"

export const metadata = {
  title: `${pageNumber} Pass Additional Data to Medusa's API Route`,
}

# {metadata.title}

In this chapter, you'll learn how to pass additional data in requests to Medusa's API Route.

## Why Pass Additional Data?

Some of Medusa's API Routes accept an `additional_data` parameter whose type is an object. The API Route passes the `additional_data` to the workflow, which in turn passes it to its hooks.

This is useful when you have a link from your custom module to a commerce module, and you want to perform an additional action when a request is sent to an existing API route.

For example, the [Create Product API Route](!api!/admin#products_postproducts) accepts an `additional_data` parameter. If you have a data model linked to it, you consume the `productsCreated` hook to create a record of the data model using the custom data and link it to the product.

### API Routes Accepting Additional Data

<Details summaryContent="API Routes List">

- Campaigns
    - [Create Campaign](!api!/admin#campaigns_postcampaigns)
    - [Update Campaign](!api!/admin#campaigns_postcampaignsid)
- Cart
    - [Create Cart](!api!/store#carts_postcarts)
    - [Update Cart](!api!/store#carts_postcartsid)
- Customers
    - [Create Customer](!api!/admin#customers_postcustomers)
    - [Update Customer](!api!/admin#customers_postcustomersid)
    - [Create Address](!api!/admin#customers_postcustomersidaddresses)
    - [Update Address](!api!/admin#customers_postcustomersidaddressesaddress_id)
- Draft Orders
    - [Create Draft Order](!api!/admin#draft-orders_postdraftorders)
- Orders
    - [Complete Orders](!api!/admin#orders_postordersidcomplete)
    - [Cancel Order's Fulfillment](!api!/admin#orders_postordersidfulfillmentsfulfillment_idcancel)
    - [Create Shipment](!api!/admin#orders_postordersidfulfillmentsfulfillment_idshipments)
    - [Create Fulfillment](!api!/admin#orders_postordersidfulfillments)
- Products
    - [Create Product](!api!/admin#products_postproducts)
    - [Update Product](!api!/admin#products_postproductsid)
    - [Create Product Variant](!api!/admin#products_postproductsidvariants)
    - [Update Product Variant](!api!/admin#products_postproductsidvariantsvariant_id)
    - [Create Product Option](!api!/admin#products_postproductsidoptions)
    - [Update Product Option](!api!/admin#products_postproductsidoptionsoption_id)
- Promotions
    - [Create Promotion](!api!/admin#promotions_postpromotions)
    - [Update Promotion](!api!/admin#promotions_postpromotionsid)

</Details>

---

## How to Pass Additional Data

### 1. Specify Validation of Additional Data

Before passing custom data in the `additional_data` object parameter, you must specify validation rules for the allowed properties in the object.

To do that, use the middleware route object defined in `src/api/middlewares.ts`.

For example, create the file `src/api/middlewares.ts` with the following content:

```ts title="src/api/middlewares.ts"
import { defineMiddlewares } from "@medusajs/medusa"
import { z } from "zod"

export default defineMiddlewares({
  routes: [
    {
      method: "POST",
      matcher: "/admin/products",
      additionalDataValidator: {
        brand: z.string().optional(),
      },
    },
  ],
})
```

The middleware route object accepts an optional parameter `additionalDataValidator` whose value is an object of key-value pairs. The keys indicate the name of accepted properties in the `additional_data` parameter, and the value is [Zod](https://zod.dev/) validation rules of the property.

In this example, you indicate that the `additional_data` parameter accepts a `brand` property whose value is an optional string.

<Note>

Refer to [Zod's documentation](https://zod.dev) for all available validation rules.

</Note>

### 2. Pass the Additional Data in a Request

You can now pass a `brand` property in the `additional_data` parameter of a request to the Create Product API Route.

For example:

```bash
curl -X POST 'http://localhost:9000/admin/products' \
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer {token}' \
--data '{
    "title": "Product 1",
    "additional_data": {
        "brand": "Acme"
    }
}'
```

<Note title="Tip">

Make sure to replace the `{token}` in the authorization header with an admin user's authentication token.

</Note>

In this request, you pass in the `additional_data` parameter a `brand` property and set its value to `Acme`.

The `additional_data` is then passed to hooks in the `createProductsWorkflow` used by the API route.

---

## Use Additional Data in a Hook

<Note>

Learn about workflow hooks in [this guide](../../workflows/workflow-hooks/page.mdx).

</Note>

Step functions consuming the workflow hook can access the `additional_data` in the first parameter.

For example, consider you want to store the data passed in `additional_data` in the product's `metadata` property.

To do that, create the file `src/workflows/hooks/product-created.ts` with the following content:

```ts title="src/workflows/hooks/product-created.ts"
import { StepResponse } from "@medusajs/framework/workflows-sdk"
import { createProductsWorkflow } from "@medusajs/medusa/core-flows"
import { Modules } from "@medusajs/framework/utils"

createProductsWorkflow.hooks.productsCreated(
  async ({ products, additional_data }, { container }) => {
    if (!additional_data.brand) {
      return
    }

    const productModuleService = container.resolve(
      Modules.PRODUCT
    )

    await productModuleService.upsertProducts(
      products.map((product) => ({
        ...product,
        metadata: {
          ...product.metadata,
          brand: additional_data.brand,
        },
      }))
    )

    return new StepResponse(products, {
      products,
      additional_data,
    })
  }
)
```

This consumes the `productsCreated` hook, which runs after the products are created.

If `brand` is passed in `additional_data`, you resolve the Product Module's main service and use its `upsertProducts` method to update the products, adding the brand to the `metadata` property.

### Compensation Function

Hooks also accept a compensation function as a second parameter to undo the actions made by the step function.

For example, pass the following second parameter to the `productsCreated` hook:

```ts title="src/workflows/hooks/product-created.ts"
createProductsWorkflow.hooks.productsCreated(
  async ({ products, additional_data }, { container }) => {
    // ...
  },
  async ({ products, additional_data }, { container }) => {
    if (!additional_data.brand) {
      return
    }

    const productModuleService = container.resolve(
      Modules.PRODUCT
    )

    await productModuleService.upsertProducts(
      products
    )
  }
)
```

This updates the product to their original state before adding the brand to their `metadata` property.