[BUG] [Python] Discriminator Not Generated or Used When Subtypes Have Duplicate Property Names or No Unique Properties

[MaxHuber03]

Description

When generating client code from an OpenAPI 3.0 specification using openapi-generator (version 7.13.0), the generator fails to generate or use the discriminator for polymorphic deserialization if:

• Two or more subtypes define properties with the same name (e.g., both have a property called value or data).
• Some subtypes have no unique properties at all.

openapi-generator version

7.13.0

OpenAPI declaration file content

This is a minimal example

components:
  schemas:
    BaseType:
      type: object
      discriminator:
        propertyName: "@type"
      properties:
        id:
          type: integer
        "@type":
          type: string
    SubTypeA:
      allOf:
        - $ref: '#/components/schemas/BaseType'
        - type: object
          properties:
            value:
              type: string
    SubTypeB:
      allOf:
        - $ref: '#/components/schemas/BaseType'
        - type: object
          properties:
            value:
              type: string
  

Generation Details

In the config file I added:

"useOneOfDiscriminatorLookup": true,

Result

The generator does not generate code that uses the discriminator for deserialization.
In Python, deserialization fails with a "multiple matches found" exception.

Suggest a fix

The generator should either emit a clear error/warning during generation or support discriminator-based deserialization as long as the discriminator property is present in the payload, regardless of duplicate property names.
At minimum, this limitation should be clearly documented.

Workaround

Ensure that all subtypes have at least one unique property name, or use the discriminator property with a unique value for each subtype.