Populating parameter using Depends() ignores pydantic model config

[dmig-alarstudios]

I use Depends() to populate model from query parameters. Recently noticed, that dependency resolving somehow ignores pydantic model configuration. According to #1474, it may be the same issue.

Environment

• OS: linux
• FastAPI Version [e.g. 0.3.0]: 0.61
• Python version: 3.8.2

Testcase

from pydantic import BaseModel, Field
from fastapi import Depends, FastAPI

app = FastAPI()

class TestParams(BaseModel):
    class Config:
        allow_population_by_field_name = True

    param: bool = Field(False, alias='alias')


@app.get('/')
async def main(params: TestParams = Depends()):
    return params.dict()

Expected results

$ curl "http://127.0.0.1:8000/?param=true"
{"param":true}

$ curl "http://127.0.0.1:8000/?alias=true"
{"param":true}

Actual results

$ curl "http://127.0.0.1:8000/?param=true"
{"param":false}

$ curl "http://127.0.0.1:8000/?alias=true"
{"param":true}

[SirTelemak]

Somehow name param in request validation is equal to alias. I'll try to make PR with fix today

EDIT: I dig inside much better and doubt it will be easy fix:

def get_typed_signature(call: Callable) -> inspect.Signature:
    signature = inspect.signature(call)

That's how FastAPI getting signature of Model on validation so there is no info about real name. I'll continue researching a bit more but now it looks like quite difficult task :)

[dmig-alarstudios]

Yeah, the problem is there by design. I believe the same issue would be with Path/Body model instantiation:

• FastAPI shouldn't pick query string parameters by names -- proper way would be to pass all of them to pydantic model
• that would also solve another minor issue: using exclude_unset=True on models .dict()/.json() has no effect now, because all model fields are being passed by FastAPI

[jrversteegh]

@SirTelemak

Somehow name param in request validation is equal to alias.

That's by design? name is the name in python, alias is the name in the API, whether json body or query string. At least, that is how I understand it.

so there is no info about real name.

Not true, I believe. If you have:

async def f(p: int = Query(..., alias='q')):
    pass

then:

inspect.signature(f).parameters['p'].default.alias == 'q'

[SirTelemak]

@jrversteegh you right that alias and name here is different things but FastAPI (if I remember correctly this case) redefines initial model and creates duplicate where name equal to alias (if exists) or name. And that why i said "there is no info about real name." since we creating new model that knows nothing about initial one

[jrversteegh]

@SirTelemak

redefines initial model and creates duplicate where name equal to alias (if exists) or name

I highly doubt that since I'm able to use aliases that aren't valid python variable names like in

async def f(page_size: int = Query(..., alias='page[size]')):
    pass

[YuriiMotov]

For now there is no option in openapi to specify aliases for parameters.
Seems that for now the only option is to duplicate parameter, make both of them optional and manually handle conflict if both are passed or no one is passed.