variable in openapi 3.0 response schema

I have a legacy REST endpoint, which I would like to adress using openapi 3.0.

The Endpoint uses a path variable:

path: action/{action}s/

and also uses this path variable in the response schema like:

response in json:

{
  "name": "someName",
  "{action}": "someActionName",
  "{action}Id": 5
}

I couldn't find a explaination about this in the openapi guide. Is it possible to generate an openapi 3.0 spec with such a request? If yes, how would this example look like?

with this:

openapi: 3.0.0
info:
  title: My API
  version: 1.0.0
paths:
  /myaction/{action}s:
    get:
      summary: Get information for a specific action
      operationId: getActionInfo
      parameters:
        - name: action
          in: path
          required: true
          description: The name of the action
          schema:
            type: string
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  name:
                    type: string
                    description: The name of the response object
                  {action}:
                    type: string
                    description: The name of the action
                  {action}Id:
                    type: integer
                    description: The ID of the action
                required:
                  - name
                  - {action}
                  - {action}Id

in editor.swagger.io, I get a parser error in line 31. (The line with "{action}Id:")

It looks like you are trying to define logic within your schema. Openapi does not support the ability to define a key based upon a user defined parameter. At most, you could use openapi polymorphic responses to define a potential response based upon the user's input. For example:

openapi: 3.0.0
info:
  title: My API
  version: 1.0.0
paths:
  /myaction/{action}s:
    get:
      summary: Get information for a specific action
      operationId: getActionInfo
      parameters:
        - name: action
          in: path
          required: true
          description: The name of the action
          schema:
            type: string
            enum:
              - create
              - delete
              - update
              - get
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  name:
                    type: string
                    description: The name of the response object
                oneOf:
                  - $ref: '#/components/schemas/CreateAction'
                  - $ref: '#/components/schemas/DeleteAction'
                  - $ref: '#/components/schemas/UpdateAction'
                  - $ref: '#/components/schemas/GetAction'
                required:
                  - name
components:
  schemas:
    CreateAction:
      type: object
      required:
        - create
        - createId
      properties:
        create:
          type: string
          description: The name of the action
        createId:
          type: integer
          description: The ID of the action
    DeleteAction:
      required:
        - delete
        - deleteId
      type: object
      properties:
        delete:
          type: string
          description: The name of the action
        deleteId:
          type: integer
          description: The ID of the action
    UpdateAction:
      type: object
      required:
        - update
        - updateId
      properties:
        update:
          type: string
          description: The name of the action
        updateId:
          type: integer
          description: The ID of the action
    GetAction:
      type: object
      required:
        - get
        - getId
      properties:
        get:
          type: string
          description: The name of the action
        getId:
          type: integer
          description: The ID of the action

This will allow you to define the response based upon the request. If going this route, I highly suggest using an enum as the action, to ensure only the proper response can be sent back.

However, another option would be to change the response altogether. You could do something like this, and it would look cleaner and be more scalable.

openapi: 3.0.0
info:
  title: My API
  version: 1.0.0
paths:
  /myaction/{action}s:
    get:
      summary: Get information for a specific action
      operationId: getActionInfo
      parameters:
        - name: action
          in: path
          required: true
          description: The name of the action
          schema:
            $ref: '#/components/schemas/Actions'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  name:
                    type: string
                    description: The name of the response object
                  action:
                    type: object
                    required:
                      - name
                      - type
                      - id
                    properties:
                      type:
                        $ref: '#/components/schemas/Actions'
                      name:
                        type: string
                        description:  The name of the action
                      id:
                        type: integer
                        description: The ID of the action
components:
  schemas:
    Actions:
      type: string
      description: The action to perform
      enum:
        - push
        - pull
        - punch
        - kick

One thing of note here is that this is just an example. I don't recommend using enums in responses, as a change to your response could break any consumers of your api.

Yes, partial segment path templates are supported by all versions of the OpenAPI specification.