^{Originally posted by harpaj March 23, 2023}

First Check

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Example Code

from typing import Annotated

from fastapi import FastAPI, Form
from pydantic import Json, BaseModel

app = FastAPI()


class JsonListModel(BaseModel):
    json_list: Json[list[str]]


@app.post("/working")
async def working(json_list: Annotated[str, Form()]) -> list[str]:
    model = JsonListModel(json_list=json_list)
    return model.json_list


@app.post("/broken")
async def broken(json_list: Annotated[Json[list[str]], Form()] ) -> list[str]:
    return json_list

Description

In the example code above, I would expect working and broken to be approximately equivalent.
However, while working returns the parsed json_list as expected, broken fails with

{"detail":[{"loc":["body","json_list"],"msg":"JSON object must be str, bytes or bytearray","type":"type_error.json"}]}

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.95.0

Python Version

Python 3.10.8

Additional Context

sample request that fails with broken and works with working:

import requests
import json

headers = {"Content-Type": "application/x-www-form-urlencoded"}
response = requests.post(
    "http://0.0.0.0:8000/broken",
    data={"json_list": json.dumps(["abc", "def"])},
    headers=headers,
)
```</div>