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Example Code

from fastapi import Form
from typing import Annotated

from fastapi import FastAPI

app = FastAPI()


@app.post("/")
def read_root(
        form_session_id: Annotated[str | None, Form(alias="sessionid")] = None,
):
    return form_session_id

Description

Sending a request with sessionid in the form data to this root endpoint returns null:

> curl  --form sessionid=123qwe http://127.0.0.1:8000/
null

With fastapi==0.112.2 it returns 123qwe.

Interestingly with 0.113.0 and a "blind" declaration of sessionid as form value it also works.

@app.post("/")
def read_root(
        form_session_id: Annotated[str | None, Form(alias="sessionid")] = None,
        sessionid: Annotated[str | None, Form()] = None,
):
    return form_session_id

(note that im not returning the blind sessionid but the form_session_id, anyhow this makes the difference).

Operating System

Linux, macOS

Operating System Details

No response

FastAPI Version

0.113.0

Pydantic Version

2.9.0

Python Version

3.12.1

Additional Context

No response