Optional nullable query parameter raise 422 error

[chbndrhnns]

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Example Code

import fastapi
import httpx
from pydantic import UUID4

app = fastapi.FastAPI()


@app.get("/")
async def get(my_param: UUID4 = fastapi.Query(None, nullable=True)):
    return {"my_param": my_param}


async def test_can_get():
    async with httpx.AsyncClient(app=app, base_url="http://mytesthost.com") as client:
        res = await client.get("/", params={"my_param": None})
        assert res.status_code == 200, res.content

Description

• Run the test and expect it to pass
• The test fails

Error:

{"detail":[{"loc":["query","my_param"],"msg":"value is not a valid uuid","type":"type_error.uuid"}]}

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.74.1

Python Version

3.9.9

Additional Context

No response

[chbndrhnns]

I found a related issue. The reason I'd like to use a UUID type and not just str is to indicate what format is expected.

[ComicShrimp]

You could try to use Optional[] in the parameter. the final code will be something like this:

import fastapi
import httpx
from pydantic import UUID4
from typing import Optional

app = fastapi.FastAPI()


@app.get("/")
async def get(my_param: Optional[UUID4] = fastapi.Query(None, nullable=True)):
    return {"my_param": my_param}


async def test_can_get():
    async with httpx.AsyncClient(app=app, base_url="http://mytesthost.com") as client:
        res = await client.get("/", params={"my_param": None})
        assert res.status_code == 200, res.content

That way not only the query parameter will be optional, but the variable will be optional too.
I hope that it helps !!!

[chbndrhnns]

I thought so, too. But when I run your snippet with FastAPI 0.77, it fails with a 422.

[ComicShrimp]

Well, the other thing that could cause the problem is that you're passing the parameters on the request. If the value is None, you can just omit the parameter.

import fastapi
import httpx
from pydantic import UUID4
from typing import Optional

app = fastapi.FastAPI()


@app.get("/")
async def get(my_param: Optional[UUID4] = fastapi.Query(None, nullable=True)):
    return {"my_param": my_param}


async def test_can_get():
    async with httpx.AsyncClient(app=app, base_url="http://mytesthost.com") as client:
        res = await client.get("/")
        assert res.status_code == 200, res.content

[chbndrhnns]

I intended to capture this null value and perform a special operation in the null case. I dropped this idea after understanding that it's also hard to differentiate between an incoming null and a default None

However, I assumed that setting nullable to True means: This field can be passed as null.

[chbndrhnns]

I understand now that the query parameters are received as a string. Sending "?some_val=null" might also cause problems if "null" is a valid option for "some_val". In this case, it's impossible to distinguish between the valid option and nothing.

[edugmes]

I have the exact same problem (except it's an UUID). Has anybody got a solution for that on Python 3.10 and Fastapi 0.88.0?