[BUG] oneOf(List,Object) not correctly working with to_dict

[FrankEssenberger]

Bug Report Checklist

• [x] Have you provided a full/minimal spec to reproduce the issue?
• [x] Have you validated the input using an OpenAPI validator (example)?
• [x] Have you tested with the latest master to confirm the issue still exists?
• [x] Have you searched for related issues/PRs?
• [x] What's the actual output vs expected output? ~~- [ ] [Optional] Sponsorship to speed up the bug fix or feature request (example)~~

Description

When you have a spec containing a oneOf with a list of objects and a single object the generated to_dict looks like:

        if hasattr(self.actual_instance, "to_dict") and callable(self.actual_instance.to_dict):
            return self.actual_instance.to_dict()     
        else:
            # primitive type
            return self.actual_instance

However, the list object does not have a to_dict so the individual elements do not get serialized in case the object is the list type. Something like this should be there:

        if hasattr(self.actual_instance, "to_dict") and callable(self.actual_instance.to_dict):
            return self.actual_instance.to_dict()
        elif isinstance(self.actual_instance, list):
            return [item.to_dict() for item in self.actual_instance]
        else:
            # primitive type
            return self.actual_instance

Actual behavior with the properties not converted: Expected behavior with the dicts:

openapi-generator version

Version 7.4.0 exetued

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Sample API
  version: 0.0.1
servers:
  - url: http://api.example.com/v1
paths:
  /users:
    get:
      responses:
        '200':    # status code
          description: A JSON array of user names
          content:
            application/json:
                schema:
                    $ref: "#/components/schemas/output"

components:
  schemas:
    list_prop:
      type: array
      items:
        $ref: "#/components/schemas/object_prop"

    object_prop:
      type: object
      properties:
        name:
          type: string

    output:
      oneOf:
      - $ref: "#/components/schemas/object_prop"
      - $ref: "#/components/schemas/list_prop"

Generation Details

We use the docker container to run the generator:

docker run --rm -v ${PWD}/src:/src openapitools/openapi-generator-cli:v7.4.0 generate -i /src/spec/minimal.yaml -g python -o /src/tmp --package-name test.v1.generated --additional-properties=generateAliasAsModel=false

Steps to reproduce

Take the spec and generate then execute the following:

import json
from v1.generated.models.output import Output

o = Output.from_json(json.dumps([{"name":'foo'},{"name":'bar'}]))
o.to_dict() #shows the unconverted dict entries

Related issues/PRs

I found an issue for the parsing: https://github.com/OpenAPITools/openapi-generator/issues/14986 but want to use not the from_jsonbut the to_dict.

Suggest a fix

If there is a union type like Union[List[SomeObject],SomeOtherObject] do in the to_dict() method add a check if the current object is of type list. If so loop over the items and call the to_dict() on each individual item (see above). Potentially in the loop one should also check once more if the iten is a primitive type, then one should just put it in the list of course.