# Links between Payment Module and Other Modules

This document showcases the module links defined between the Payment Module and other Commerce Modules.

## Summary

The Payment Module has the following links to other modules:

|First Data Model|Second Data Model|Type|Description|
|---|---|---|---|
|Cart|PaymentCollection|Stored - one-to-one|Learn more|
|Customer|AccountHolder|Stored - many-to-many|Learn more|
|Order|PaymentCollection|Stored - one-to-many|Learn more|
|OrderClaim|PaymentCollection|Stored - one-to-many|Learn more|
|OrderExchange|PaymentCollection|Stored - one-to-many|Learn more|
|Region|PaymentProvider|Stored - many-to-many|Learn more|

***

## Cart Module

The Cart Module provides cart-related features, but not payment processing.

Medusa defines a link between the `Cart` and `PaymentCollection` data models. A cart has a payment collection which holds all the authorized payment sessions and payments made related to the cart.

Learn more about this relation in [this documentation](https://docs.medusajs.com/commerce-modules/payment/payment-collection#usage-with-the-cart-module).

### Retrieve with Query

To retrieve the cart associated with the payment collection with [Query](https://docs.medusajs.com/learn/fundamentals/module-links/query), pass `cart.*` in `fields`:

### query.graph

```ts
const { data: paymentCollections } = await query.graph({
  entity: "payment_collection",
  fields: [
    "cart.*",
  ],
})

// paymentCollections[0].cart
```

### useQueryGraphStep

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

// ...

const { data: paymentCollections } = useQueryGraphStep({
  entity: "payment_collection",
  fields: [
    "cart.*",
  ],
})

// paymentCollections[0].cart
```

### Manage with Link

To manage the payment collection of a cart, use [Link](https://docs.medusajs.com/learn/fundamentals/module-links/link):

### link.create

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

// ...

await link.create({
  [Modules.CART]: {
    cart_id: "cart_123",
  },
  [Modules.PAYMENT]: {
    payment_collection_id: "paycol_123",
  },
})
```

### createRemoteLinkStep

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

// ...

createRemoteLinkStep({
  [Modules.CART]: {
    cart_id: "cart_123",
  },
  [Modules.PAYMENT]: {
    payment_collection_id: "paycol_123",
  },
})
```

***

## Customer 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.

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

### Retrieve with Query

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

### query.graph

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

// accountHolders[0].customer
```

### useQueryGraphStep

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

// ...

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

// accountHolders[0].customer
```

### Manage with Link

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

### link.create

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

// ...

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

### createRemoteLinkStep

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

// ...

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

***

## Order Module

An order's payment details are stored in a payment collection. This also applies for claims and exchanges.

So, Medusa defines links between the `PaymentCollection` data model and the `Order`, `OrderClaim`, and `OrderExchange` data models.

![A diagram showcasing an example of how data models from the Order and Payment modules are linked](https://res.cloudinary.com/dza7lstvk/image/upload/v1716554726/Medusa%20Resources/order-payment_ubdwok.jpg)

### Retrieve with Query

To retrieve the order of a payment collection with [Query](https://docs.medusajs.com/learn/fundamentals/module-links/query), pass `order.*` in `fields`:

### query.graph

```ts
const { data: paymentCollections } = await query.graph({
  entity: "payment_collection",
  fields: [
    "order.*",
  ],
})

// paymentCollections[0].order
```

### useQueryGraphStep

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

// ...

const { data: paymentCollections } = useQueryGraphStep({
  entity: "payment_collection",
  fields: [
    "order.*",
  ],
})

// paymentCollections[0].order
```

### Manage with Link

To manage the payment collections of an order, use [Link](https://docs.medusajs.com/learn/fundamentals/module-links/link):

### link.create

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

// ...

await link.create({
  [Modules.ORDER]: {
    order_id: "order_123",
  },
  [Modules.PAYMENT]: {
    payment_collection_id: "paycol_123",
  },
})
```

### createRemoteLinkStep

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

// ...

createRemoteLinkStep({
  [Modules.ORDER]: {
    order_id: "order_123",
  },
  [Modules.PAYMENT]: {
    payment_collection_id: "paycol_123",
  },
})
```

***

## Region Module

You can specify for each region which payment providers are available. The Medusa application defines a link between the `PaymentProvider` and the `Region` data models.

![A diagram showcasing an example of how resources from the Payment and Region modules are linked](https://res.cloudinary.com/dza7lstvk/image/upload/v1711569520/Medusa%20Resources/payment-region_jyo2dz.jpg)

This increases the flexibility of your store. For example, you only show during checkout the payment providers associated with the cart's region.

### Retrieve with Query

To retrieve the regions of a payment provider with [Query](https://docs.medusajs.com/learn/fundamentals/module-links/query), pass `regions.*` in `fields`:

### query.graph

```ts
const { data: paymentProviders } = await query.graph({
  entity: "payment_provider",
  fields: [
    "regions.*",
  ],
})

// paymentProviders[0].regions
```

### useQueryGraphStep

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

// ...

const { data: paymentProviders } = useQueryGraphStep({
  entity: "payment_provider",
  fields: [
    "regions.*",
  ],
})

// paymentProviders[0].regions
```

### Manage with Link

To manage the payment providers in a region, use [Link](https://docs.medusajs.com/learn/fundamentals/module-links/link):

### link.create

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

// ...

await link.create({
  [Modules.REGION]: {
    region_id: "reg_123",
  },
  [Modules.PAYMENT]: {
    payment_provider_id: "pp_stripe_stripe",
  },
})
```

### createRemoteLinkStep

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

// ...

createRemoteLinkStep({
  [Modules.REGION]: {
    region_id: "reg_123",
  },
  [Modules.PAYMENT]: {
    payment_provider_id: "pp_stripe_stripe",
  },
})
```