fastapi form data with pydantic model

Question

I am trying to submit data from html forms and on the validate it with pydantic model.
Using this code

from fastapi import FastAPI, Form
from pydantic import BaseModel
from starlette.responses import HTMLResponse


app = FastAPI()

@app.get("/form", response_class=HTMLResponse)
def form_get():
    return '''<form method="post"> 
    <input type="text" name="no" value="1"/> 
    <input type="text" name="nm" value="abcd"/> 
    <input type="submit"/> 
    </form>'''


class SimpleModel(BaseModel):
    no: int
    nm: str = ""

@app.post("/form", response_model=SimpleModel)
def form_post(form_data: SimpleModel = Form(...)):
    return form_data

How ever I get the error with http status 422 Unprocessable Entity

{"detail":[{"loc":["body","form_data"],"msg":"field required","type":"value_error.missing"}]}

Equivalent curl command (generated by firfox) is

curl 'http://localhost:8001/form' -H 'Content-Type: application/x-www-form-urlencoded' --data 'no=1&nm=abcd'

Here the request body contains no=1&nm=abcd

What am i doing wrong?

Answer 1

I found a solution which can help us to use FastAPI forms as pydantic as well :)
My code:

class AnyForm(BaseModel):
    any_param: str
    any_other_param: int = 1

    @classmethod
    def as_form(
        cls,
        any_param: str = Form(...),
        any_other_param: int = Form(1)
    ) -> AnyForm:
        return cls(any_param=any_param, any_other_param=any_other_param)

@router.post('')
async def any_view(form_data: AnyForm = Depends(AnyForm.as_form)):
        ...

It's showed in the swagger as usual form
I think, it can be written more generic, maybe I will return and edit the answer.

[UPDATED]

I've written it more generic as a decorator

import inspect
from typing import Type

from fastapi import Form
from pydantic import BaseModel
from pydantic.fields import ModelField

def as_form(cls: Type[BaseModel]):
    new_parameters = []

    for field_name, model_field in cls.__fields__.items():
        model_field: ModelField  # type: ignore

        if not model_field.required:
            new_parameters.append(
                inspect.Parameter(
                    model_field.alias,
                    inspect.Parameter.POSITIONAL_ONLY,
                    default=Form(model_field.default),
                    annotation=model_field.outer_type_,
                )
            )
        else:
            new_parameters.append(
                inspect.Parameter(
                    model_field.alias,
                    inspect.Parameter.POSITIONAL_ONLY,
                    default=Form(...),
                    annotation=model_field.outer_type_,
                )
            )

    async def as_form_func(**data):
        return cls(**data)

    sig = inspect.signature(as_form_func)
    sig = sig.replace(parameters=new_parameters)
    as_form_func.__signature__ = sig  # type: ignore
    setattr(cls, 'as_form', as_form_func)
    return cls

And usage looks like

class Test1(BaseModel):
    a: str
    b: int


@as_form
class Test(BaseModel):
    param: str
    test: List[Test1]
    test1: Test1
    b: int = 1
    a: str = '2342'


@router.post('/me', response_model=Test)
async def me(request: Request, form: Test = Depends(Test.as_form)):
    return form