[Question]: Ref handling in discriminator mappings doesn't allow different discriminator keys to map to the same entity?

[IgorMaj]

Question

Hello, I'm using your library as part of the following component (openapi-generator), and I've already posted an issue here. In the snippet below, you can see what I'm trying to do. I'm trying to map different discriminator property values to the same entity. However, it results in an error.

Affected Version

2.0.30 (at least), seems to be introduced here.

I'm using 2.0.30

Context

      responses:
        '200':
          description: "List of all the objects."
          content:
            application/json:
              schema:
                type: array
                items:
                  oneOf:
                    - $ref: '#/components/schemas/TypeA'
                    - $ref: '#/components/schemas/TypeB'
                  discriminator:
                    propertyName: discriminatorProperty
                    mapping:
                      ONE: '#/components/schemas/TypeA'
                      TWO: '#/components/schemas/TypeB'
                      THREE: '#/components/schemas/TypeB'
                      FOUR: '#/components/schemas/TypeB'
                      FIVE: '#/components/schemas/TypeB'

Additional Details

This is the error:
java.lang.IllegalStateException: Duplicate key #/components/schemas/TypeB (attempted merging values TWO and THREE)

Checklist

• [ y] I have searched the existing issues and documentation before asking.
• [ y] I have provided enough information for others to understand my question.

[ewaostrowska]

Hi @IgorMaj,
Thanks for pointing the issue!
I have changed the status here to Bug since the Discriminator Object should not require the mapping's values to be unique.

The java.util.stream.Collectors.duplicateKeyException implies that the keys and values have been inverted and this is confirmed by the attached commit.

We encourage you to provide a pull request for this issue :)

[IgorMaj]

Small update: Unable to reproduce on my local machine, even though the relevant class hasn't changed. Can't get it to run the buggy code path even with external files for schemas. The problematic code block seems to be unreachable:

I expected the following test to fail:

@Test
    public void testIssue2222() {
        SwaggerParseResult result = new OpenAPIParser().readLocation("issue-2222/openapi.yaml", null, null);

        assertNotNull(result.getOpenAPI());
    }

However, it passes and ExternalRefProcessor::processSchema doesn't get called.

openapi.yaml:

openapi: 3.0.1
info:
  title: Example API
  version: 1.0.0
  description: Example API demonstrating polymorphic response with external schemas.

paths:
  /objects:
    get:
      summary: Get all objects
      operationId: getObjects
      responses:
        '200':
          description: "List of all the objects."
          content:
            application/json:
              schema:
                type: array
                items:
                  oneOf:
                    - $ref: './schemas.yaml#/components/schemas/TypeA'
                    - $ref: './schemas.yaml#/components/schemas/TypeB'
                  discriminator:
                    propertyName: discriminatorProperty
                    mapping:
                      ONE: './schemas.yaml#/components/schemas/TypeA'
                      TWO: './schemas.yaml#/components/schemas/TypeB'
                      THREE: './schemas.yaml#/components/schemas/TypeB'
                      FOUR: './schemas.yaml#/components/schemas/TypeB'
                      FIVE: './schemas.yaml#/components/schemas/TypeB'

schemas.yaml:

info:
  title: Shared Schemas
  version: 1.0.0

components:
  schemas:
    BaseType:
      type: object
      required:
        - discriminatorProperty
      properties:
        discriminatorProperty:
          type: string
          description: A property used to determine the concrete object type.
          enum: [ONE, TWO, THREE, FOUR, FIVE]
        id:
          type: string
          description: Unique identifier for the object.

    TypeA:
      allOf:
        - $ref: '#/components/schemas/BaseType'
        - type: object
          properties:
            discriminatorProperty:
              type: string
              enum: [ONE]
            name:
              type: string
              description: A name specific to TypeA.

    TypeB:
      allOf:
        - $ref: '#/components/schemas/BaseType'
        - type: object
          properties:
            discriminatorProperty:
              type: string
              enum: [TWO, THREE, FOUR, FIVE]
            value:
              type: number
              description: A numeric value specific to TypeB.

Could be missing something.

[ewaostrowska]

I have manged to reproduce the error here

The issue seems to be that the error appears in the logical path for the reference paths as can be seen in the OpenAPITools/openapi-generator#21766

   at io.swagger.v3.parser.processors.ExternalRefProcessor.processSchema (ExternalRefProcessor.java:253)
    at io.swagger.v3.parser.processors.ExternalRefProcessor.processSchema (ExternalRefProcessor.java:244)
    at io.swagger.v3.parser.processors.ExternalRefProcessor.processRefSchemaObject (ExternalRefProcessor.java:1009)
    at io.swagger.v3.parser.processors.ExternalRefProcessor.processPathItem (ExternalRefProcessor.java:350)
    at io.swagger.v3.parser.processors.ExternalRefProcessor.processRefToExternalPathItem (ExternalRefProcessor.java:325)
    at io.swagger.v3.parser.processors.PathsProcessor.processReferencePath (PathsProcessor.java:346)
    at io.swagger.v3.parser.processors.PathsProcessor.processPaths (PathsProcessor.java:68)

[IgorMaj]

Thanks. You can take a look at the PR here:
#2249

Let me know what you think, or whether I need to do additional updates. Thanks for the help.