Path parameter became required if it defined via Pydantic model

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Example Code

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

app = FastAPI()

class Foo(BaseModel):
    bar: str = Field(Path('bar'))  # default value is defined

@app.get('/foo')  # always will return 422 because `bar` not represent in path
async def pathless_handler(params: Foo = Depends(Foo)):     
    pass

@app.get('/foo/{bar}')
async def path_aware_handler(params: Foo = Depends(Foo)):
    pass

Description

If the path parameters are defined via Pydantic model, then the path parameters become always required.

curl -v localhost:8000/foo
*   Trying 127.0.0.1:8000...
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET /foo HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.83.1
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 422 Unprocessable Entity
< date: Fri, 10 Jun 2022 11:56:49 GMT
< server: uvicorn
< content-length: 87
< content-type: application/json
<
* Connection #0 to host localhost left intact
{"detail":[{"loc":["path","bar"],"msg":"field required","type":"value_error.missing"}]}% 

The root of evil is in this line (it makes a path parameter always required, even if a default value is specified 😢) https://github.com/tiangolo/fastapi/blob/1876ebc77949a9a254909ec61ea0c09365169ec2/fastapi/params.py#L85

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.78.0

Python Version

3.10.4

Additional Context

No response

[gtors]

As ad-hoc solution:

from typing import Any
from fastapi.params import Path as OrigPath, Undefined

class Path(OrigPath):

    def __init__(self, default: Any = Undefined, *args, **kwargs):
        super().__init__(*args, **kwargs)

        if default is not Undefined:
            self.default = default

[tiangolo]

Ah, yeah @NickVeld , I was focusing on the original post. So, the thing is, I’m not sure I understand what would be the intention of the original question, what would be expected in that case. I’m not sure what would mean to have a default value for a path parameter. I think I’m missing the explanation of what was expected, and what was @gtors intending to achieve.

Now, if you have a specific use case that needs something related to this, please create a new issue, following the template, and please make sure you add what are you intending to solve and what behavior you would have expected.