Not rendering multi-select in API doc while using Pydantic model

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn’t find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google “How to X in FastAPI” and didn’t find any information.
• I already read and followed all the tutorial in the docs and didn’t find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

import typing
from fastapi import FastAPI, Query, Depends
from pydantic import BaseModel
from enum import Enum

app = FastAPI()


class Status(str, Enum):
    SUCCESS = "SUCCESS"
    REFUND = "REFUND"
    FAIL = "FAIL"
    CANCEL = "CANCEL"


@app.get("/working-example/")
async def root_with_normal_query_params(status_in: typing.List[Status] = Query(...)):
    return {"status_inputs": status_in}


class StatusModel(BaseModel):
    status_in: typing.List[Status]


@app.get("/not-working-example/")
async def root_with_pydantic(status_inputs: StatusModel = Depends()):
    return {"status_inputs": status_inputs}

Description

The API docs are not generating the multi-select option while using the Pydantic model for the query/request parser.

without using Pydantic model

with using Pydantic model

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.70.1

Python Version

Python 3.9.11

Additional Context

No response

[iudeen]

You can use dataclass from Pydantic.

import typing
from enum import Enum

from fastapi import FastAPI, Query, Depends
from pydantic.dataclasses import dataclass

app = FastAPI()


class Status(str, Enum):
    SUCCESS = "SUCCESS"
    REFUND = "REFUND"
    FAIL = "FAIL"
    CANCEL = "CANCEL"


@app.get("/working-example/")
async def root_with_normal_query_params(status_in: typing.List[Status] = Query(...)):
    return {"status_inputs": status_in}


@dataclass
class StatusModel:
    status_in: list[Status] = Query(...)


@app.get("/not-working-example/")  # it now works
async def root_with_pydantic(status_inputs: StatusModel = Depends()):
    return {"status_inputs": status_inputs}

[jerinpetergeorge]

@jerinpetergeorge if you are happy with the solution, you can close this and open a ISSUE/BUG to discuss on why the “normal” approach is not working, and probably finding a better solution!

I’m kind of okay with the solution since we’re still not sure “why” FastAPI doesn’t support it - is that on purpose? Or a bug?

Also, I hope this current GH issue considers a bug - or I wrote like that in the first place, which makes me think that it is better not to close this GH issue at the moment.

I would be super happy if someone could change the label of this issue from https://github.com/tiangolo/fastapi/labels/question to https://github.com/tiangolo/fastapi/labels/bug