> ## 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.

# The order group

> The aggregate record over a multi-seller purchase, its display id, and cart link.

This page covers the order group record and how it aggregates the per-seller
orders created from a single cart.

## Order group

An order group is the shopper-facing wrapper over a multi-seller purchase. It is
represented by the `OrderGroup` data model (table `order_group`, id prefix
`og`). When a cart containing offers from more than one seller is completed, the
cart is split into one child order per seller. All of those orders are attached
to a single group.

```ts theme={null}
const OrderGroup = model.define("order_group", {
  id: model.id({ prefix: "og" }).primaryKey(),
  display_id: model.autoincrement(),
  seller_count: model.number().computed(),
  customer_id: model.text().nullable(),
  total: model.bigNumber().computed(),
  cart_id: model.text(),
})
```

The group carries a human-readable `display_id`, an auto-incrementing integer,
so shoppers and operators can reference the purchase without exposing the
internal id. `customer_id` records who placed it. `seller_count` and `total`
are computed at read time. See [Computed totals](/platform/order-group/concepts/computed-totals).

<Note>
  A group is created even for a single-seller cart, so every completed
  marketplace order has exactly one parent group regardless of how many sellers
  it spans.
</Note>

## The cart link

Each group holds a `cart_id` pointing back to the cart it was created from. This
is exposed as a **read-only** link to the Cart module. The cart is frozen
(`completed_at` is set) the moment the split runs, so the reference is a
historical record, not something you write through.

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

<Tip>
  Because the cart is immutable after checkout, the `cart_id` is safe to treat as
  a stable audit pointer to the exact basket the shopper paid for.
</Tip>

## Child orders

The group doesn't store line items itself. Those live on the child `Order`
records, linked through the `order_group_order` table. Loading a group's
`orders.*` gives you each seller's slice, each with its own fulfillment, payment,
returns, and refunds.