Optional bool in query string always True when parameter not present

[LKay]

Describe the bug

When query parameter of type Optional[bool] is declared using Query class parameter value is not correctly mapped and instead of None it maps to instance of Schema which when type casted to bool returns True.

To Reproduce

Sample code:

class QueryParams(BaseModel):
	foo: Optional[bool] = None

async def query_params(foo: Optional[bool] = Query(None, description="Some parameter")):
	return QueryParams(foo=foo)

@api.get("/foo")
async def get(data: QueryParams = Depends(query_params)):
	# When '/foo' is called (without any parameters) the 'foo' parameter 
  # inside 'data' has value of 'True' instead of 'None'.
	return None

It however works fine if declared as just:

async def query_params(foo: Optional[bool] = None):
	return QueryParams(foo=foo)

Expected behavior
Value should be assigned only if parameter is present in query string, None otherwise.

Environment:

• OS: macOS
• FastAPI Version: 0.35
• Python version: 3.7.3

[dmontagu]

@LKay
I can't reproduce this; the following test passes for me on the current version:

from typing import Optional

from pydantic import BaseModel
from starlette.testclient import TestClient

from fastapi import FastAPI, Depends, Query

app = FastAPI()


class QueryParams(BaseModel):
    foo: Optional[bool] = None


async def query_params(foo: Optional[bool] = Query(None, description="Some parameter")):
    return QueryParams(foo=foo)


@app.get("/foo")
async def get(data: QueryParams = Depends(query_params)):
    # When '/foo' is called (without any parameters) the 'foo' parameter
    # inside 'data' has value of 'True' instead of 'None'.
    return data.foo


def test_optional_bool():
    assert TestClient(app).get("/foo").content == b"null"

Did I miss something?

[LKay]

Oh, sorry I missed one more part. It happens when there is another wrapping function for parameters ie. for admin and non-admin parameters, such as:

class QueryParams(BaseModel):
    foo: Optional[bool] = None
    bar: Optional[bool] = None # ie. only admin param

async def query_params_admin(foo: Optional[bool] = Query(None, description="Some parameter"), bar: Optional[bool] = Query(None, description="Some parameter")):
    return QueryParams(foo=foo, bar=bar)

async def query_params(foo: Optional[bool] = Query(None, description="Some parameter")):
    return await query_params_admin(foo)

[dmontagu]

The problem in your example is that you are calling query_params_admin directly -- FastAPI can only perform dependency injection if the function is called as a result of Depends. (Note: this is not a bug in fastapi.)

If you make a self-contained example like the one I posted above that isn't working the way you'd expect, I can show you options for how to refactor it into something that works.

[LKay]

I got it. I refactored my code so I now have two function, both returning instance of my parameters models class.

[tiangolo]

Thanks for the help @dmontagu ! 🙇‍♂️ 🚀

Thanks for reporting back and closing the issue @LKay 🎉