I am trying to submit form-data with a Pydantic model.

from dataclasses import dataclass
from typing import Annotated

from fastapi import FastAPI, Form, Depends, Response, status
from pydantic import BaseModel


class SimpleModel(BaseModel):
    title: str = Form(...)
    content: str = Form(...)


@dataclass
class SimpleDataclass:
    title: str = Form(...)
    content: str = Form(...)


app = FastAPI()


@app.post("/post", status_code=status.HTTP_201_CREATED)
def create_post(request: SimpleModel = Depends()):
    return Response(status_code=201)


@app.post("/post2", status_code=status.HTTP_201_CREATED)
def create_post(request: SimpleDataclass = Depends()):
    return Response(status_code=201)

/post takes a Pydantic BaseModel but it treats as query params, not form-data. Then I replace SimpleModel by SimpleDataclass and I got /post2, this works as expected.

The question is why BaseModel doesn’t work for me? I can’t use dataclass so is there a way to make it work with BaseModel?