> ## 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 change pipeline

> The ProductChange record, its immutability, and the audit trail.

In this document, you'll learn how a product edit is captured and why the
pipeline is built on immutable records.

## Product change

A product change is a single reviewable edit to one product, represented by the
`ProductChange` data model (table `product_change`, id prefix `prodch`). It
references the target product through `product_id`, carries the `status` of the
review, and records who created and resolved it (`created_by`, `confirmed_by`,
`declined_by`, `canceled_by`) with matching timestamps.

```ts theme={null}
const productChangeModuleService = container.resolve(MercurModules.PRODUCT_EDIT)

const change = await productChangeModuleService.retrieveProductChange(id, {
  relations: ["actions"],
})
```

A change owns one or more `ProductChangeAction` records (`actions`). The change
is the reviewable unit; the actions are the individual operations it will apply.
See [Change actions](/platform/product-edit/concepts/change-actions).

<Note>
  A product can have **only one active (pending) change at a time**. Staging a
  new change while one is still pending is rejected. The vendor resolves or
  cancels the open change first.
</Note>

## Immutability & the audit trail

A change is never rewritten in place. It is created, its actions are appended,
and it is resolved by moving `status` forward and stamping the actor and time.
Because nothing is overwritten, the set of `ProductChange` rows on a product is a
durable history of who changed what and who approved it.

Some events aren't vendor edits at all, such as a publish approval or a revision
request. They still belong in the history. Those are recorded as changes created
already `confirmed`, so the audit trail captures them without waiting on review.

```ts theme={null}
await recordProductAuditChangeWorkflow(container).run({
  input: {
    actor_id: "user_123",
    changes: [
      {
        product_id: "prod_123",
        external_note: "Approved for publish",
        actions: [
          { product_id: "prod_123", action: "STATUS_CHANGE", details: { status: "published" } },
        ],
      },
    ],
  },
})
```

<Tip>
  Read a product's full history through the read-only `product.changes` link
  (see the [Links reference](/platform/product-edit/reference/links)) rather than
  querying the module directly. The link keeps the audit trail attached to the
  product.
</Tip>