OpenAPI 3: How to require one or more properties in PATCH requestBody?

Question

I have a User resource:

I want to define a PATCH /users/{uid} so that the client can update image, bio or both.

An example valid request body would be:

{
  "image": "filename.jpg",
  "bio": "My biography"
}

If the image property is sent alone the existing bio property will remain the same on the server and only the image will be updated. If both are sent (as above) both will change.

In short:

• an empty request body {} is disallowed.

• {"image": "new.jpg"}, {"bio": "new bio" or {"image": "new.jpg", "bio": "new bio" is allowed.

This is what I have so far. I'm using the anyOf object with two separate type: objects within. I've tried this with Swagger hub using the virtserver, but the virtual server always seems to return 200 OK and passes back the example data regardless of whatever is passed, so I have no way to know.

Does my definition do what I intended? If not, what the best practice?

openapi: 3.0.0
    ...
    
    patch:
      summary: update a user
      parameters:
        - in: path
          name: uid
          description: user id
          schema:
            type: string
          required: true
      requestBody:
        description: Update a user's profile
        content:
          application/json:
            schema:
              type: object
              anyOf:
                - type: object
                  properties:
                    image:
                      type: string
                - type: object
                  properties:
                    bio:
                      type: string
              additionalProperties: false
        required: true
      responses:
        '200':
          description: Successfully updated
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/User'