> Documentation index: [Saleor](/llms.txt) · [This section](/api-usage/llms.txt)
> Source: https://docs.saleor.io/api-usage/external-references

# External References

`externalReference` is a feature designed to link an object to an ID from an external system. This can be particularly useful when incorporating Saleor with other services.

For example, suppose we aim to synchronize Saleor with a CMS. If a product is introduced in Saleor, we would also want to generate a corresponding product in the CMS. Upon creation of a product in the CMS, an ID is assigned. This ID can then be used to update the `externalReference` of the product in Saleor:

```graphql
mutation {
  productUpdate(externalReference: "CMS_ID", input: { name: "New name" }) {
    errors {
      field
      message
    }
  }
}
```

`externalReference` is available in the following types:

-   [Order](/api-reference/orders/objects/order.md#external-reference) - starting from version 3.19, the [MANAGE\_ORDERS](/api-reference/users/enums/permission-enum.md#manage-orders) permission is required to use `externalReference` with [order](/api-reference/orders/queries/order.md#external-reference) query.
-   [Product](/api-reference/products/objects/product.md#external-reference)
-   [ProductVariant](/api-reference/products/objects/product-variant.md#external-reference)
-   [Attribute](/api-reference/attributes/objects/attribute.md#external-reference)
-   [AttributeValue](/api-reference/attributes/objects/attribute-value.md#external-reference)
-   [Warehouse](/api-reference/products/objects/warehouse.md#external-reference)
-   [User](/api-reference/users/objects/user.md#external-reference)

note

The `externalReference` value must be unique across a single type. The maximum length is 250 characters.