💭 python - How to use a Pydantic model with Form data in FastAPI...
Waylon Walker
Learning in Public @_WaylonWalker
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Here's my thought on 💭 python - How to use a Pydantic model with Form data in FastAPI...
I went down the route of leveraging the json-enc extention in
htmx
loading glossary
, but later realized that this completely breaks browsers/users who do not wish to use javascript. While most of the web would feel quite broken with javascript disabled, I don't want to contribute to that without good reason.
Taking a second look into this issue, rather than using json-enc, and using as_form to get form data into a model keeps the nice DX fo everything being a pydantic model, but the site still works without js. with js htmx kicks in, you get a spa like experience by loading partials onto the page, and without, you just get a full page reload.
the implementation
copied from https://stackoverflow.com/questions/60127234/how-to-use-a-pydantic-model-with-form-data-in-fastapi
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
new_parameters.append(
inspect.Parameter(
model_field.alias,
inspect.Parameter.POSITIONAL_ONLY,
default=Form(...) if model_field.required else Form(model_field.default),
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 the usage looks like
@as_form
class Test(BaseModel):
param: str
a: int = 1
b: str = '2342'
c: bool = False
d: Optional[float] = None
@router.post('/me', response_model=Test)
async def me(request: Request, form: Test = Depends(Test.as_form)):
return form
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