OpenAPI spec generated for union type with discriminator, generate default value instead of enum to allow using openapi-generator-maven-plugin

[Joachim Van der Auwera (joachimvda)]

I have a union type like this:

@discriminated(#{ envelope: "none", discriminatorPropertyName: "type" })
union Pet {
    CAT: Cat,
    DOG: Dog
}

model Cat {
    type: "CAT";
    meows: boolean;
}

model Dog {
    type: "DOG";
    barks: boolean;
}

This generates the following model

    Pet:
      type: object
      oneOf:
        - $ref: '#/components/schemas/Cat'
        - $ref: '#/components/schemas/Dog'
      discriminator:
        propertyName: type
        mapping:
          CAT: '#/components/schemas/Cat'
          DOG: '#/components/schemas/Dog'
    Cat:
      type: object
      required:
        - type
        - meows
      properties:
        type:
          type: string
          enum:
            - CAT
        meows:
          type: boolean
    Dog:
      type: object
      required:
        - type
        - barks
      properties:
        type:
          type: string
          enum:
            - DOG
        barks:
          type: boolean

which does not work for openapi-generator-maven-plugin. Specifically the enum in the subtypes should be a default value instead. Is there a way to force the type property to be generated with a default string instead to produce

    Cat:
      type: object
      required:
        - type
        - meows
      properties:
        type:
          type: string
          default: "CAT"
        meows:
          type: boolean
    Dog:
      type: object
      required:
        - type
        - barks
      properties:
        type:
          type: string
          default: "DOG"
        barks:
          type: boolean

This does produce working code when using openapi-generator-maven-plugin.

Thanks for the help

[Joachim Van der Auwera (joachimvda)]

In another attempt, I tried using something like

@discriminated(#{ envelope: "none", discriminatorPropertyName: "type" })
union Pet {
    CAT: Cat,
    DOG: Dog
}

model Cat {
    type: string = "CAT";
    meows: boolean;
}

model Dog {
    type: string = "DOG";
    barks: boolean;
}

This does not work as it produces errors

error invalid-discriminated-union-variant: Variant "CAT" explicitly defines the discriminator property "type" but the value "" do not match the variant name "CAT"
error invalid-discriminated-union-variant: Variant "DOG" explicitly defines the discriminator property "type" but the value "" do not match the variant name "DOG"

[Joachim Van der Auwera (joachimvda)]

Found a workaround

@discriminated(#{ envelope: "none", discriminatorPropertyName: "type" })
union Pet {
    CAT: Cat,
    DOG: Dog
}

model PetBase {
  type: string;
}

model Cat extends PetBase {
    meows: boolean;
}

model Dog extends PetBase {
    barks: boolean;
}