> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mercurjs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Links to other modules

> How the Order Group domain links to carts, orders, sellers, and offers.

Modules in Mercur never reference each other directly. They connect through
**module links**. The `OrderGroup` entity (owned by the Seller module) sits at
the center of a completed multi-seller purchase, linking the cart it came from to
the per-seller orders it produced. Once a link is defined, you retrieve related
records with `query.graph` using the link alias.

```ts theme={null}
const { data: groups } = await query.graph({
  entity: "order_group",
  fields: ["id", "display_id", "cart.id", "orders.id", "orders.total"],
})
```

## Group links

| Linked module | Relationship                                                                                                                    |
| ------------- | ------------------------------------------------------------------------------------------------------------------------------- |
| **Cart**      | A group references the one cart it was created from (`order_group.cart_id`, **read-only**). Carts are immutable after checkout. |
| **Order**     | A group has many child orders, one per seller, through the `order_group_order` table.                                           |

## Order links

The child orders produced by the split carry their own marketplace links:

| Linked module | Relationship                                                                                                                                                    |
| ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Seller**    | Each order belongs to one seller (`order_order_seller_seller`); a seller has many orders.                                                                       |
| **Offer**     | Each order line item links to the offer it was purchased from (`order_line_item` → `offer`, list on the line-item side so one offer can back many order lines). |

<Note>
  The `cart_id` link is resolved from the field on the group and can't be written
  through the link itself. The split sets it once, at creation.
</Note>

<Tip>
  To scope a group to a single seller, filter its child orders by
  `orders.seller.id`. The list workflow does exactly this when you pass a
  `sellerId`. See [List order groups](/platform/order-group/guides/list-order-groups).
</Tip>