Query default value cannot be set in Annotated when using APIRouter

[tlinhart]

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Example Code

# main.py

from fastapi import FastAPI
from router import router

app = FastAPI()
app.include_router(router)

# router.py

from typing import Annotated
from fastapi import APIRouter, Query

router = APIRouter()

@router.get("/")
async def root(*, n: Annotated[float, Query()] = 50):
    return {"n": n}

Description

When starting the Uvicorn server using uvicorn main:app, I receive:

Traceback (most recent call last):
  File "/home/pasmen/tmp/x-annotated-query-router/./venv/bin/uvicorn", line 8, in <module>
    sys.exit(main())
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/uvicorn/main.py", line 403, in main
    run(
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/uvicorn/main.py", line 568, in run
    server.run()
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/uvicorn/server.py", line 59, in run
    return asyncio.run(self.serve(sockets=sockets))
  File "/usr/lib/python3.10/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/uvicorn/server.py", line 66, in serve
    config.load()
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/uvicorn/config.py", line 471, in load
    self.loaded_app = import_from_string(self.app)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/uvicorn/importer.py", line 21, in import_from_string
    module = importlib.import_module(module_str)
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/home/pasmen/tmp/x-annotated-query-router/main.py", line 5, in <module>
    app.include_router(router)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/fastapi/applications.py", line 427, in include_router
    self.router.include_router(
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/fastapi/routing.py", line 782, in include_router
    self.add_api_route(
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/fastapi/routing.py", line 600, in add_api_route
    route = route_class(
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/fastapi/routing.py", line 446, in __init__
    self.dependant = get_dependant(path=self.path_format, call=self.endpoint)
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/fastapi/dependencies/utils.py", line 303, in get_dependant
    type_annotation, depends, param_field = analyze_param(
  File "/home/pasmen/tmp/x-annotated-query-router/venv/lib/python3.10/site-packages/fastapi/dependencies/utils.py", line 387, in analyze_param
    assert field_info.default is Undefined or field_info.default is Required, (
AssertionError: `Query` default value cannot be set in `Annotated` for 'n'. Set the default value with `=` instead.

Operating System

Linux

Operating System Details

lsb_release -a:

No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04.2 LTS
Release:	22.04
Codename:	jammy

FastAPI Version

0.95.0

Python Version

Python 3.10.6

Additional Context

This should work according to the documentation about default values. Also, it works when not using APIRouter but having the path operation directly on app.

[jonra1993]

I have the same problem this happens also when the time is date and enum those endpoints are also in a router. I have this error message in both cases for the moment the solution is not using Annotated:

AssertionError: Querydefault value cannot be set inAnnotated for

Working code

    user_status: IUserStatus = Query(
        default=IUserStatus.active,
        title= "User status",
        description="User status, It is optional. Default is active",
    ),

Failing code

 user_status: Annotated[
        IUserStatus, 
        Query(        
            title= "User status",
            description="User status, It is optional. Default is active",
        )
    ] = IUserStatus.active,

Working code

    start_date: date = Query(default=(datetime.now() - timedelta(days=7)).date()),
    end_date: date = Query(default=datetime.now().date()),

Failing code

    start_date: Annotated[date, Query(title="start date for get data")] = datetime.now() - timedelta(days=7),
    end_date: Annotated[date, Query(title="end date for get data")] = datetime.now().date(),

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[jonra1993]

Thanks @tiangolo it works perfectly :)

[hochstibe]

I have the same problem, it depends on the ordering: If everything is in one file, the router can be added before defining the endpoint.
If the router is in a separate file (like tlinhart), this is not possible. The same error resulted in Header, Path or Query parameters.

from typing import Annotated
from fastapi import FastAPI, Header, APIRouter

app = FastAPI()

@app.get("/app")
async def read_items(user_agent: Annotated[str | None, Header()] = None):
    return {"User-Agent": user_agent}

test_router = APIRouter()


# if the router is added before defining the route, it works fine
# app.include_router(test_router)

@test_router.get("/router")
async def read_items(user_agent: Annotated[str | None, Header()] = None):
    return {"User-Agent": user_agent}

# breaks
app.include_router(test_router)

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[EricHuang0525]

I am facing the same problem here. This only happens when endpoints use APIRouter but not FastAPI.

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[AlexanderPodorov]

Just want to put my 2 cents into this topic. Those dependencies don't work either:

# function dependency
def common_parameters(
        q: Annotated[str | None, Query()] = 'asd',
        skip: Annotated[int, Query()] = 4,
        limit: Annotated[int, Query()] = 5
):
    return {"q": q, "skip": skip, "limit": limit}


# class as dependency
class CommonQueryParams:
    def __init__(
            self,
            q: Annotated[str | None, Query()] = None,
            skip: Annotated[int, Query()] = 0,
            limit: Annotated[int, Query()] = 100
    ):
        self.q = q
        self.skip = skip
        self.limit = limit


# dataclass as dependency (in order to get pregenerated __init__)
@dataclass
class CommonQueryParamsDC:
    q: Annotated[str | None, Query()] = None
    skip: Annotated[int, Query()] = 0
    limit: Annotated[int, Query()] = 100

The same error message is returned.

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[AlexanderPodorov]

Could be unrelated issue, I'm using pydantic dataclass for Query dependencies. This way I'm benefiting from automatic aliasing provided by CustomBaseModel (alias_generator is defined there). This code works:

@dataclass(config=CustomBaseModel.Config)
class PaginationGet:
    page: int = Query(1, gt=0)
    per_page: PerPage = Query(PerPage.VALUE_025)
    all_items: bool = Query(False)

This code does not work:

@dataclass(config=CustomBaseModel.Config)
class PaginationGet:
    page: Annotated[int, Query(gt=0)]
    per_page: Annotated[PerPage, Query()]
    all_items: Annotated[bool, Query()]

The error is this:
ValueError: cannot specify Annotated and value Fields together for 'page'

[tiangolo]

Hum, this is actually not currently supported in FastAPI, if it works it's a bit by "accident" 😅

But I want to have a way to support things like this in the future. 🤓

[jonra1993]

Why this is in discussions when it seems a bug on the apirouter of latest fastapi ?

[jack-michaud]

When I searched the issues evaluating the upgrade to FastAPI 0.95.0, I saw a small amount of issues and none of them bugs with the new version. If I saw this thread, I would have re-evaluated since my large project does use APIRouters... It would be helpful to upgrade discussions to Issues more proactively.

[tlinhart]

@jack-michaud agreed. I might be wrong but there seem to be no guidelines for reporting issues. I've gone through https://fastapi.tiangolo.com/contributing but it doesn't talk about reporting bugs. Seeing how most of the issues were transferred into discussions, I thought that would be the way to go.

[hochstibe]

I see the point with only allowing discussions. But then the bug reports should be regularly converted as issues....

[leokhachatorians]

This entire concept of blanket migrating all issues into discussions is ridiculous. It's literally sweeping crap under the couch and pretending your living room is clean.

[tiangolo]

Thanks for the feedback.

Yep, here's the issue: #9387

@leokhachatorians I would appreciate if you tried to be a bit more gentle with your words, you're getting open source free software, for free, please, at least try to be kind.

---

For more context to all, before migrating to Discussions, around 90% of the "issues" were questions. And before that, when it was possible to report "bugs", 90% of the reported "bugs" were actually user errors. So, unfortunately, I can't let the space open to freely create issues and/or mark them as bugs to everyone.

Answering questions (here or in issues) is what consumes most of the time, so I have to try and structure it the best way I can and try to reduce the noise, to also be able to work a bit on the code, docs, etc.

If any of you has the chance, your help by helping others with their questions here in Discussions would be greatly appreciated: https://fastapi.tiangolo.com/help-fastapi/#help-others-with-questions-in-github

[linpan]

this is error issues. @tiangolo

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[sharonyogev]

This should solve it: #9315

[tiangolo]

Thank you for the fix @sharonyogev! 🙇

This was just released in FastAPI version 0.95.1 🎉

[JeroennC]

This issue also affects the non-annotated approach, probably limited to the decorator dependencies. Minimal example:

from typing import Annotated

from fastapi import FastAPI, Header, Depends, APIRouter

app = FastAPI()


router = APIRouter()


def validate_header(x_test: Annotated[str | None, Header()] = None):
    if x_test != "test":
        raise Exception("Error")


@router.get("/", dependencies=[Depends(validate_header)])
async def root():
    return {"message": "Hello World"}


app.include_router(router)

From debugging it is caused by analyze_param being called more than once due to the include_router. analyze_param validates field_info.default in L387, but then may change it in L393. The second time analyze_param comes around is when the assertion on L387 raises an exception.

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[adriangb]

Could this be related to pydantic/pydantic#4067? Maybe it’s worth trying to update Pydantic?

[sharonyogev]

I don't think so, take a look at my comment with my PR above, it's in FastAPI, but the bug and the solution is really similar

[adriangb]

thanks for confirming

[javierguzman]

Is there a workaround in the meantime the merge comes? I am having the same issue I believe, specifically I get this error:

Cookie` default value cannot be set in `Annotated` for 'authzAccessToken'. Set the default value with `=` instead.

Thank you in advance and regards

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[brianloss]

I'm seeing this as well. The docs provide an example that causes the error. Just try to run the example here: https://fastapi.tiangolo.com/tutorial/path-params-numeric-validations/#import-path

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[gitpushdashf]

Running into this as well. Definitely seems like a bug.

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[n8sty]

Can you all try your use cases with the fix from #9279 (comment)? If it works, confirm on this thread and if it doesn't note that too

[javierguzman]

I did not know I could install from Github with pip...I am going to give a try as well thanks @fnep

[hochstibe]

The fix solves my issue

[bkis]

Tested it. Same here. #9315 would fix the issue for me, too.

[javierguzman]

Working for me as well

[tiangolo]

Thanks for the idea @n8sty! 🤓 ☕

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[espdev]

I have the same problem in my project structure something like this:

app
  __init__.py
  api
      __init__.py
      routes.py
  main.py

# routes.py

from typing import Annotated
from fastapi import APIRouter, Query

router = APIRouter()

@router.get('/hello')
async def hello(name: Annotated[str | None, Query(description='Your name')] = None):
    return f'Hello {name or "noname"}!'

# main.py

from fastapi import FastAPI
from app import api

app = FastAPI()
app.include_router(api.router)

There is an exception:

AssertionError: `Query` default value cannot be set in `Annotated` for 'name'. Set the default value with `=` instead.

I tried running the code in the debugger and found out that the analyze_param function is called twice for the query parameter.

The first call is correct, and it sets the default value for the query parameter:

And the second call is failed because the default value is already set for the query parameter:

I think this is a bug in FastAPI. Signatures and parameters should not be re-analyzed. This is non-idempotent behavior anyway.

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[mateoradman]

It's been really long now. Is this problem even considered an issue? The docs of v0.95.0 make it seem like this is definitely expected to work but it doesn't. It would be great if either the proposed solution #9315 gets reviewed and merged, or docs get updated explicitly stating this limitation of the "Annotated approach". In case of latter, please remove the tip Prefer to use the Annotated version if possible. which is shown in many sections of the documentation.

[leokhachatorians]

As far as I know he's the only one with write access

[mateoradman]

With so many individuals and companies using and essentially relying on FastAPI nowadays, having a single contributor calling all the shots is suboptimal for a project of this size and importance.

[Kludex]

This problem is considered an issue. @tiangolo is already aware of it.

[mateoradman]

Thanks for letting us know @Kludex 🙂

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

@mateoradman your help would be much appreciated: https://fastapi.tiangolo.com/help-fastapi/

Actually, most of the work that needs to be done is not hitting the "merge" button, but reviewing PRs: https://fastapi.tiangolo.com/help-fastapi/#review-pull-requests

And answering questions: https://fastapi.tiangolo.com/help-fastapi/#help-others-with-questions-in-github

For the next time, you could go to the PR and add a review with a comment explaining how you tested the code and how it solved your problem. 🤓 That would be much appreciated and would help and speed up things a lot! ☕

[jdiaz-lw]

I have been bitten by this as well, worst of all is that I was preparing a POC to introduce FastAPI in my company so that we could adopt it across the whole Python teams :/ I think having the docs with those directions and not working like this can be a put off for tech leads assessing the adoption of the library.

[tiangolo]

This should be fixed in #9315

Just released in FastAPI 0.95.1 🎉

[mateoradman]

Thanks for merging it and letting us know, @tiangolo 🙂

[druidance]

Hey,

It seems this still isn't working. Using this code snippet
v: Annotated[list[str], Query(default=[])]
gives me
AssertionError: 'Query' default value cannot be set in 'Annotated' for 'v'. Set the default value with '=' instead.

I don't want to use current workaround
v: Annotated[list[str], Query()] = []
because I want to use Depends as a default value. But it also doesn't work.

Any suggestions how to solve this issue?

FastAPI Version
0.110.0

Python Version
Python 3.11.6

[sharonyogev]

For this I had this PR:
#9389
But @tiangolo didn't want to merge it

[druidance]

Thank you for the PR. I will have to use another workaround then :-/