FastAPI Form handlng that doesn't suck

fa_post.py

# Source https://github.com/fastapi/fastapi/discussions/7268#discussioncomment-6993634
from fastapi import Form


def form_body(cls):
    """
    Converts a Pydantic BaseModel into FastAPI Form Body.

    Usage:

    @form_body
    class OItem(BaseModel):
        name: str
        num: int | None = None

    # or

    Item = form_body(aq.ClientAvailabilityCreate)
    # Do this to not corrupt the original class, or for code generation.

    @router.post('/test', response_model=Item)
    def endpoint(item: Item = Depends(Item)):
        return item
    """
    params = []
    for arg in cls.__signature__.parameters.values():
        arg_type = str(arg).split(":")[1]
        new_arg = arg.replace(default=Form(...))
        if "Optional" in arg_type:  # TODO: make this support new style | None
            new_arg = arg.replace(default=Form(None))
        params.append(new_arg)

    cls.__signature__ = cls.__signature__.replace(parameters=params)

    return cls

TODO: Make it work with modern foo: str | None = None typehints.

This is now supported natively in FastAPI 0.113.0. https://fastapi.tiangolo.com/tutorial/request-form-models/