medusa-store/www/apps/resources/app/commerce-modules/customer/links-to-other-modules/page.mdx

import { CodeTabs, CodeTab } from "docs-ui"

export const metadata = {
  title: `Links between Customer Module and Other Modules`,
}

# {metadata.title}

This document showcases the module links defined between the Customer Module and other commerce modules.

## Summary

The Customer Module has the following links to other modules:

<Note title="Tip">

Read-only links are used to query data across modules, but the relations aren't stored in a pivot table in the database.

</Note>

- [`Customer` data model \<\> `AccountHolder` data model of Payment Module](#payment-module).
- [`Cart` data model of Cart Module \<\> `Customer` data model](#cart-module). (Read-only).
- [`Order` data model of Order Module \<\> `Customer` data model](#order-module). (Read-only).

---

## Payment Module

Medusa defines a link between the `Customer` and `AccountHolder` data models, allowing payment providers to save payment methods for a customer, if the payment provider supports it.

<Note>

This link is available starting from Medusa `v2.5.0`.

</Note>

### Retrieve with Query

To retrieve the account holder associated with a customer with [Query](!docs!/learn/fundamentals/module-links/query), pass `customer.*` in `fields`:

<CodeTabs group="relation-query">
  <CodeTab label="query.graph" value="method">

```ts
const { data: customers } = await query.graph({
  entity: "customer",
  fields: [
    "account_holder.*",
  ],
})

// customers.account_holder
```

  </CodeTab>
  <CodeTab label="useQueryGraphStep" value="step">

```ts
import { useQueryGraphStep } from "@medusajs/medusa/core-flows"

// ...

const { data: customers } = useQueryGraphStep({
  entity: "customer",
  fields: [
    "account_holder.*",
  ],
})

// customers.account_holder
```

  </CodeTab>
</CodeTabs>

### Manage with Link

To manage the account holders of a customer, use [Link](!docs!/learn/fundamentals/module-links/link):

<CodeTabs group="relation-link">
  <CodeTab label="link.create" value="method">

```ts
import { Modules } from "@medusajs/framework/utils"

// ...

await link.create({
  [Modules.CUSTOMER]: {
    customer_id: "cus_123",
  },
  [Modules.PAYMENT]: {
    account_holder_id: "acchld_123",
  },
})
```

  </CodeTab>
  <CodeTab label="createRemoteLinkStep" value="step">

```ts
import { createRemoteLinkStep } from "@medusajs/medusa/core-flows"

// ...

createRemoteLinkStep({
  [Modules.CUSTOMER]: {
    customer_id: "cus_123",
  },
  [Modules.PAYMENT]: {
    account_holder_id: "acchld_123",
  },
})
```

  </CodeTab>
</CodeTabs>

---

## Cart Module

Medusa defines a read-only link between the `Customer` data model and the [Cart Module](../../cart/page.mdx)'s `Cart` data model. This means you can retrieve the details of a customer's carts, but you don't manage the links in a pivot table in the database. The customer of a cart is determined by the `customer_id` property of the `Cart` data model.

### Retrieve with Query

To retrieve a customer's carts with [Query](!docs!/learn/fundamentals/module-links/query), pass `carts.*` in `fields`:

<CodeTabs group="relation-query">
  <CodeTab label="query.graph" value="method">

```ts
const { data: customers } = await query.graph({
  entity: "customer",
  fields: [
    "carts.*",
  ],
})

// customers.carts
```

  </CodeTab>
  <CodeTab label="useQueryGraphStep" value="step">

```ts
import { useQueryGraphStep } from "@medusajs/medusa/core-flows"

// ...

const { data: customers } = useQueryGraphStep({
  entity: "customer",
  fields: [
    "carts.*",
  ],
})

// customers.carts
```

  </CodeTab>
</CodeTabs>

---

## Order Module

Medusa defines a read-only link between the `Customer` data model and the [Order Module](../../order/page.mdx)'s `Order` data model. This means you can retrieve the details of a customer's orders, but you don't manage the links in a pivot table in the database. The customer of an order is determined by the `customer_id` property of the `Order` data model.

### Retrieve with Query

To retrieve a customer's orders with [Query](!docs!/learn/fundamentals/module-links/query), pass `orders.*` in `fields`:

<CodeTabs group="relation-query">
  <CodeTab label="query.graph" value="method">

```ts
const { data: customers } = await query.graph({
  entity: "customer",
  fields: [
    "orders.*",
  ],
})

// customers.orders
```

  </CodeTab>
  <CodeTab label="useQueryGraphStep" value="step">

```ts
import { useQueryGraphStep } from "@medusajs/medusa/core-flows"

// ...

const { data: customers } = useQueryGraphStep({
  entity: "customer",
  fields: [
    "orders.*",
  ],
})

// customers.orders
```

  </CodeTab>
</CodeTabs>