> ## 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 Attribute (Product Attribute) domain links to products, categories, and options.

Modules in Mercur never reference each other directly. They're connected through
**module links**. The Product Attribute module links into Medusa's product module
in several ways: to products, to categories, and, for variant axes, to product
options through mirror links. Once a link is defined, you retrieve related records
with `query.graph` using the link alias.

```ts theme={null}
const { data: products } = await query.graph({
  entity: "product",
  fields: ["id", "title", "scoped_attributes.*"],
})
```

## Products

| Link                                          | Table                          | Relationship                                                                                           |
| --------------------------------------------- | ------------------------------ | ------------------------------------------------------------------------------------------------------ |
| **Product → attribute** (`scoped_attributes`) | None                           | Read-only; a product's inline (product-scoped) attributes, resolved from `ProductAttribute.product_id` |
| **Product ↔ attribute value**                 | `product_attribute_value_link` | Many-to-many pivot; the values selected on a product                                                   |

## Categories

| Link                                    | Table                        | Relationship                                                         |
| --------------------------------------- | ---------------------------- | -------------------------------------------------------------------- |
| **Attribute ↔ category** (`categories`) | `product_category_attribute` | Many-to-many; the product categories an attribute is associated with |

## Product options (mirror links)

| Link                     | FK                                              | Relationship                                                           |
| ------------------------ | ----------------------------------------------- | ---------------------------------------------------------------------- |
| **Attribute → option**   | `ProductAttribute.product_option_id`            | Read-only 1:1; the mirror `ProductOption` for a variant-axis attribute |
| **Value → option value** | `ProductAttributeValue.product_option_value_id` | Read-only 1:1; the mirror `ProductOptionValue` for an axis value       |

<Note>
  The mirror links (Attribute → option, Value → option value) and the product
  scope link (`scoped_attributes`) are **read-only**. They're resolved from the
  FK on the owning record and can't be written through the link itself. The
  workflows keep the mirror in sync when axis attributes and values change.
</Note>