[BUG] Explicit discriminator mappings do not override defaults

[TheMrMilchmann]

Description

Given an object with oneOf and a discriminator mapping, the generator erroneously still allows the schema names as aliases during de-/serialization (even if an explicit mapping for a respective referenced schema exists).

The spec says that only the explicit mappings should be usable. (See https://swagger.io/docs/specification/v3_0/data-models/inheritance-and-polymorphism/#discriminator)

For example:

    Fruit:
      discriminator:
        mapping:
          APPLE: '#/components/schemas/Apple'
          BANANA: '#/components/schemas/Banana'
        propertyName: fruitType
      oneOf:
      - $ref: '#/components/schemas/Apple'
      - $ref: '#/components/schemas/Banana'
      properties:
        fruitType:
          $ref: '#/components/schemas/FruitType'
      required:
      - fruitType
      type: object
      x-one-of-name: Fruit
    Apple:
      properties:
        seeds:
          type: integer
      required:
      - seeds
      type: object
    Banana:
      properties:
        length:
          type: integer
      required:
      - length
      type: object

@JsonSubTypes({
  @JsonSubTypes.Type(value = Apple.class, name = "APPLE"),
  @JsonSubTypes.Type(value = Banana.class, name = "BANANA"),
  @JsonSubTypes.Type(value = Apple.class, name = "Apple"),    // <-- Wrong
  @JsonSubTypes.Type(value = Banana.class, name = "Banana")   // <-- Wrong
})

@Generated(value = "org.openapitools.codegen.languages.SpringCodegen", comments = "Generator version: 7.13.0-SNAPSHOT")
public interface Fruit {

openapi-generator version

This is present on master and affects at least 7.11.0 and 7.12.0. After digging into the code and git history, I have no reason to believe that there are unaffected versions.

OpenAPI declaration file content or URL

https://github.com/OpenAPITools/openapi-generator/blob/f39675b41af49851f05056009ccd4a823770a881/samples/openapi3/server/petstore/spring-boot-oneof/src/main/resources/openapi.yaml

Generation Details

No special set up required. Just use the sample.

Steps to reproduce

Just use the sample.

Related issues/PRs

Suggest a fix

[Mattias-Sehlstedt]

Hi, could you clarify what exact sentence(s) from https://swagger.io/docs/specification/v3_0/data-models/inheritance-and-polymorphism/#discriminator that state

The spec says that only the explicit mappings should be usable.

I am unable to read that from the descriptions present on that page.

[TheMrMilchmann]

Sorry, wrong anchor. The example in https://swagger.io/docs/specification/v3_0/data-models/inheritance-and-polymorphism/#mapping-type-names is pretty clear.

In this example, the obj1 value is mapped to the Object1 model that is defined in the same spec, obj2 – to Object2, and the value system matches the sysObject model that is located in an external file. All these objects must have the objectType property with the value "obj1", "obj2" or "system", respectively.

(Emphasis mine)