> ## 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 Review domain links to products, sellers, orders, and customers.

Modules in Mercur never reference each other directly. They connect through
**module links**. A review carries no foreign keys to its target on the model
itself. Instead, four links anchor each review to the rest of the marketplace.
Once a link is defined, you retrieve related records with `query.graph` using the
link alias.

```ts theme={null}
const { data: reviews } = await query.graph({
  entity: "review",
  fields: ["id", "rating", "product.*", "seller.*"],
})
```

## Targets

| Linked module | Relationship                                                                                         |
| ------------- | ---------------------------------------------------------------------------------------------------- |
| **Product**   | A product has many reviews (`product_product_review_review`). Written when `reference` is `product`. |
| **Seller**    | A seller has many reviews (`seller_seller_review_review`). Written when `reference` is `seller`.     |

A review is linked to **either** a product or a seller, never both. The
`reference` field on the review decides which link is created.

## Provenance

| Linked module | Relationship                                                                            |
| ------------- | --------------------------------------------------------------------------------------- |
| **Order**     | Each review is linked to the order that earned it (`order_order_review_review`).        |
| **Customer**  | Each review is linked to the customer who wrote it (`customer_customer_review_review`). |

These two links are written for every review and back the validation that a
customer can review a target only once per order.

<Note>
  All four links are list links (`isList: true`) on the owning side. A product,
  seller, order, or customer has many reviews.
</Note>