💭 python - How to use a Pydantic model with Form data in FastAPI...
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!https://stackoverflow.com/questions/60127234/how-to-use-a-pydantic-model-with-form-data-in-fastapi

Date: August 8, 2023

External Link stackoverflow.com

I went down the route of leveraging the json-enc extention in htmx </htmx/>, 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
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copied from https://stackoverflow.com/questions/60127234/how-to-use-a-pydantic-model-with-form-data-in-fastapi

[code]
  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

[code]
  @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

NOTE
│ This post is a thought </thoughts/>. It’s a short note that I make about someone else’s content online #thoughts </tags/thoughts/>