AssertionError with multiple path params and form depends

[pozsa]

First check

• I used the GitHub search to find a similar issue and didn't find it.
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• I already searched in Google "How to X in FastAPI" and didn't find any information.

Description

Considering the following class and route definition:

class DocumentUpdateForm():
    def __init__(
            self,
            date: datetime.date = fastapi.Form(...),
            file_object: Optional[fastapi.UploadFile] = fastapi.File(None),
            name: str = fastapi.Form(...),
            description: str = fastapi.Form(...),
            category: str = fastapi.Form(...),
    ) -> None:
        self.date = date
        self.file_object = file_object
        self.name = name
        self.description = description
        self.category = category

@router.put('/{date}/{uuid}')
def update_document(
    date: datetime.date,
    uuid: str,
    form_in: schema.DocumentUpdateForm = fastapi.Depends(),
) -> None:
    return

The result is AssertionError.

server_development | Traceback (most recent call last):
server_development |   File "/usr/local/lib/python3.8/multiprocessing/process.py", line 315, in _bootstrap
server_development |     self.run()
server_development |   File "/usr/local/lib/python3.8/multiprocessing/process.py", line 108, in run
server_development |     self._target(*self._args, **self._kwargs)
server_development |   File "/usr/local/lib/python3.8/site-packages/uvicorn/subprocess.py", line 73, in subprocess_started
server_development |     target(sockets=sockets)
server_development |   File "/usr/local/lib/python3.8/site-packages/uvicorn/main.py", line 341, in run
server_development |     loop.run_until_complete(self.serve(sockets=sockets))
server_development |   File "uvloop/loop.pyx", line 1456, in uvloop.loop.Loop.run_until_complete
server_development |   File "/usr/local/lib/python3.8/site-packages/uvicorn/main.py", line 348, in serve
server_development |     config.load()
server_development |   File "/usr/local/lib/python3.8/site-packages/uvicorn/config.py", line 274, in load
server_development |     self.loaded_app = import_from_string(self.app)
server_development |   File "/usr/local/lib/python3.8/site-packages/uvicorn/importer.py", line 20, in import_from_string
server_development |     module = importlib.import_module(module_str)
server_development |   File "/usr/local/lib/python3.8/importlib/__init__.py", line 127, in import_module
server_development |     return _bootstrap._gcd_import(name[level:], package, level)
server_development |   File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
server_development |   File "<frozen importlib._bootstrap>", line 991, in _find_and_load
server_development |   File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
server_development |   File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
server_development |   File "<frozen importlib._bootstrap_external>", line 783, in exec_module
server_development |   File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
server_development |   File "./app/main.py", line 7, in <module>
server_development |     from app.endpoints import country, data, document, login, user
server_development |   File "./app/endpoints/document.py", line 104, in <module>
server_development |     def update_document(
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 464, in decorator
server_development |     self.add_api_route(
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 407, in add_api_route
server_development |     route = route_class(
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 334, in __init__
server_development |     self.dependant = get_dependant(path=self.path_format, call=self.endpoint)
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/dependencies/utils.py", line 267, in get_dependant
server_development |     sub_dependant = get_param_sub_dependant(
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/dependencies/utils.py", line 102, in get_param_sub_dependant
server_development |     return get_sub_dependant(
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/dependencies/utils.py", line 138, in get_sub_dependant
server_development |     sub_dependant = get_dependant(
server_development |   File "/usr/local/lib/python3.8/site-packages/fastapi/dependencies/utils.py", line 280, in get_dependant
server_development |     assert is_scalar_field(
server_development | AssertionError: Path params must be of one of the supported types

Any ideas what is wrong? What am I missing?

If I remove form_in it works.
Similarly if I remove one of the path params (and leave form_in in) it also works.

[tiangolo]

You are declaring the same name date in 2 places, a path parameter and a form.

Consider them all as parameters of the same function, even if they are in a dependency, so one of them ends up overwriting the other.

You can change the form date to be named date_form, and then use an alias to make the form field still be date:

from typing import Union, Optional
import datetime
from fastapi import FastAPI
import fastapi

app = FastAPI()

class DocumentUpdateForm():
    def __init__(
            self,
            date_form: datetime.date = fastapi.Form(..., alias="date"),
            file_object: Optional[fastapi.UploadFile] = fastapi.File(None),
            name: str = fastapi.Form(...),
            description: str = fastapi.Form(...),
            category: str = fastapi.Form(...),
    ) -> None:
        self.date = date
        self.file_object = file_object
        self.name = name
        self.description = description
        self.category = category


@app.put('/{date}/{uuid}')
def update_document(
    date: datetime.date,
    uuid: str,
    form_in: DocumentUpdateForm = fastapi.Depends(),
) -> None:
    return

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