[BUG] [Python-Fastapi] Enum parameters typed as string instead of enum

Bug Report Checklist

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

Description

When generating a FastAPI endpoint that receives an enum parameter, the value is not properly validated before being passed to the implementation. Currently, the parameter is typed as a string instead of using an enum class, and the enum class is not generated.

openapi-generator version

v7.9.0

OpenAPI declaration file content or url

https://gist.github.com/reyescabello/6cd965708fd0b03e8eadb9f3c0c0a899#file-query_param_example-yml

Generation Details

Generated with jar:

java -jar openapi-generator-cli.jar generate -i openapi.yml -g python-fastapi -o openapi_server

Steps to reproduce

The generated code is:

@router.get(
    "/example",
    responses={
        200: {"model": QuizPaged, "description": "OK"},
        400: {"description": ""},
        401: {"description": ""},
        403: {"description": ""},
        500: {"description": ""},
    },
    tags=["Example"],
    summary="Example endpoint",
    response_model_by_alias=True,
)
async def example_get(
    status: str = Query(None, description="", alias="status"),
) -> QuizPaged:
    
    return await BaseExampleApi.subclasses[0]().example_get(status)

The expected code is something like this:

class StatusEnum(str, Enum):
    CANDIDATE = 'CANDIDATE'
    DRAFT = 'DRAFT'
    COMPLETED = 'COMPLETED'
    REVIEW_REQUIRED = 'REVIEW_REQUIRED'
    WITHDRAWN = 'WITHDRAWN'

@router.get(
    "/example",
    responses={
        200: {"model": QuizPaged, "description": "OK"},
        400: {"description": ""},
        401: {"description": ""},
        403: {"description": ""},
        500: {"description": ""},
    },
    tags=["Example"],
    summary="Example endpoint",
    response_model_by_alias=True,
)
async def example_get(
    status: StatusEnum = Query(None, description="", alias="status"),
) -> QuizPaged:
    
    return await BaseExampleApi.subclasses[0]().example_get(status)

Related issues/PRs

I think this may be related to this other issue about query params typing:

https://github.com/OpenAPITools/openapi-generator/issues/20115

Suggest a fix

Start by using the OpenAPI declaration at the linked gist and the shown Java generation command to reproduce the python-fastapi output. Compare the generated endpoint with the expected StatusEnum example; done means the enum class is generated and the endpoint parameter uses it so FastAPI validates enum values.