# parameters-unique

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

This rule checks whether the parameter lists of a Swagger 2.0 document contain
duplicates.

## Rule Details

The Swagger 2.0 specification requires a parameter list not to contain
duplicate parameters, where a parameter is identified by the combination of
its `name` and its location (`in`). With duplicates it is unclear which
definition applies.

The `parameters-unique` rule checks the `parameters` of every path item and of
every operation separately, and reports `Duplicate parameter name '<name>' in
location '<location>'` for every parameter that repeats the name and location
of an earlier parameter of the same list. Parameter references (`$ref`) are
compared by the parameter they point to; unresolved references are ignored. A
parameter with the same name in a different location (for example a query
parameter and a header both named `id`) is not a duplicate.

## Configuration

None.

## Examples

**Good**. The parameters differ by name or location.

```yaml
swagger: '2.0'
info:
  title: Pet Store
  version: 1.0.0
paths:
  /pets:
    get:
      parameters:
        - name: id
          in: query
          type: string
        - name: id
          in: header
          type: string
      responses:
        '200':
          description: A list of pets.
```

**Bad**. The inline `limit` parameter duplicates the referenced one.

```yaml
swagger: '2.0'
info:
  title: Pet Store
  version: 1.0.0
paths:
  /pets:
    get:
      parameters:
        - $ref: '#/parameters/limit'
        - name: limit
          in: query
          type: string
      responses:
        '200':
          description: A list of pets.
parameters:
  limit:
    name: limit
    in: query
    type: integer
```

## Automatic fixes

When invoked with `--fix`, this rule removes a duplicate parameter from its
list when it is structurally identical to the first parameter with the same
name and location (references are compared by their targets). Duplicates that
differ from the first parameter are reported but not fixed, since the rule
cannot tell which definition is the right one.

## When Not to Use It

We recommend to always enable this rule, since duplicate parameters 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.