[JAVA] Prioritize mapped discriminators over generated (relates to issue #12777)

[robbertvanwaveren]

This PR introduces a slightly smarter ordering of the discriminators which prioritizes actual non-generated mappings as defined in the original spec above others as suggested here #12777 (comment).

The result is that the correct value is selected to populate the discriminator field during serialization based on the actual discriminator mapping is available in the schema.

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[robbertvanwaveren]

@wing328 Could you have a look at this change?

(the failed check is inherited from the issue in master with the python-nextgen client and is not related)

[Qunit]

Helpful fix

[wing328]

can you please add a line or two explaining the change/code block?

does it aim to maintain the same order in the spec?

[robbertvanwaveren]

I've added the comment and rebased the branch with current master @wing328

[robbertvanwaveren]

rebased branch to deal with removed python samples

[b3nk4n]

Thank you! This is a really helpful fix for us!

[mcleap]

Please merge it before 7.0.1 release, we really like this feature. :) We've just faced with this issue...

[wing328]

Can someone please share a spec to reproduce the issue? I tested with the one in #12777 (comment) but the output remains the same with this patch/PR.

[robbertvanwaveren]

In the original issue different people actually refer to different issues. This PR solves the most generic of those. Namely that objects are serialized using the proper value as per the key in the discriminator spec.

I don't have time to test it right now, but I believe this spec shows the problem

openapi: 3.0.1
info:
  title: Discriminator Test spec
  version: 0.0.1
paths:
  /random-parent:
    get:
      operationId: test
      responses:
        '200':
          description: Successful operation
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Parent'
components:
  schemas:
    Parent:
      type: object
      properties:
        parent:
          type: string
        child:
          oneOf:
            - $ref: '#/components/schemas/Child1'
            - $ref: '#/components/schemas/Child2'              
    Child1:
      allOf:
        - $ref: '#/components/schemas/Child'
        - type: object
          properties:
            problematic:
              type: boolean
              default: true
    Child2:
      allOf:
        - $ref: '#/components/schemas/Child'
        - type: object
          properties:
            sweet:
              type: boolean
              default: true
    Child:
      type: object
      properties:
        name:
          type: string
        type:
          type: string
      discriminator:
        propertyName: 'type'
        mapping:
          # ProblemChild/SweetChildOfMine come alphabetically behind Child1/Child2
          ProblemChild: '#/components/schemas/Child1'
          SweetChildOfMine: '#/components/schemas/Child2'

The resulting interface "ParentChild.java" should look like this with this patch:

@JsonSubTypes({
  @JsonSubTypes.Type(value = Child1.class, name = "ProblemChild"),
  @JsonSubTypes.Type(value = Child2.class, name = "SweetChildOfMine"),
  @JsonSubTypes.Type(value = Child1.class, name = "Child1"),
  @JsonSubTypes.Type(value = Child2.class, name = "Child2"),
})

whereas without it the ordering will be different, resulting in jackson picking the wrong values during serialization.

[wing328]

FYI @OpenAPITools/generator-core-team