# operation-id-unique

Source: https://apigenie.pl/docs/linter/swagger/rules/operation-id-unique

This rule checks whether the operation IDs of a Swagger 2.0 document are
unique.

## Rule Details

The Swagger 2.0 specification requires the `operationId` to be unique among
all operations of an API. Duplicate IDs break code generators, which name
methods after them, and make links to operations ambiguous.

The `operation-id-unique` rule reports `Operation ID is not unique <id>` for
every operation that repeats an ID already used by an earlier operation, in
document order. The first occurrence is not reported. Missing and empty IDs
are ignored; the `operation-id-defined` rule reports them.

## Configuration

None.

## Examples

**Good**. Each operation has its own ID.

```yaml
swagger: '2.0'
info:
  title: Users
  version: 1.0.0
paths:
  /users:
    get:
      operationId: getUsers
      responses:
        '200':
          description: A list of users.
  /users/{id}:
    get:
      operationId: getUserById
      parameters:
        - name: id
          in: path
          required: true
          type: string
      responses:
        '200':
          description: A single user.
```

**Bad**. Two operations share the same ID.

```yaml
swagger: '2.0'
info:
  title: Downloads
  version: 1.0.0
paths:
  /downloads/{id}:
    parameters:
      - name: id
        in: path
        required: true
        type: string
    patch:
      operationId: cancelDownload
      responses:
        '200':
          description: The download was updated.
    delete:
      operationId: cancelDownload
      responses:
        '204':
          description: The download was cancelled.
```

## Automatic fixes

When invoked with `--fix`, this rule keeps the first occurrence of an ID and
replaces every later duplicate with an ID generated the same way as by the
`operation-id-defined` rule, from the HTTP method and the path (for example
`getPetsById` for `GET /pets/{id}`). IDs already used in the document are
reserved, and collisions get a numeric suffix starting at 2.

## When Not to Use It

We recommend to always enable this rule, since duplicate operation IDs violate
the Swagger 2.0 specification.

## Compatibility

This rule is compatible with Swagger 2.0 documents. OpenAPI 3.x documents are
linted by the OpenAPI linter, which has a rule of the same name.