Display Enum drop-down when I use Depends

[vicente23]

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Example Code

from enum import Enum

from fastapi import  Depends, FastAPI, HTTPException

app = FastAPI()

class Names(str, Enum):
    Bob = "Bob"
    Jack = "Jack"

async def name_parameter(name: str) -> Names:
    try:
        return Names(name)
    except ValueError:
        raise HTTPException(detail="wrong name", status_code=422)

@app.get("/")
async def root(name_valid_representation: Names,
               name_wrong_representation: Names = Depends(name_parameter)
):
    return {"message": f"Hello"}

Description

For my application, I use several Enum.

I need to customize the error messages automatically returned by pydantic.

For this, I use a parameter of type Enum and the Depends method which allows me to customize the error message using the HTTPException method.

This works, but I noticed that when using Depends, the dropdown list with the allowed values no longer appears.

Is there a way to display this dropdown list while customizing the error message?

I also explored Literal typing as well, same result.

Thanks in advance for your answers

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.94.0

Python Version

3.10.6

Additional Context

No response

[jgould22]

The reason is because your dependency isnt taking an Enum any more it is taking a string so the openapi generator reflects that.

A better approach might be to write a custom exception handler to handle the exception from pydantic to return what you would prefer.

You can read some in the docs here https://fastapi.tiangolo.com/tutorial/handling-errors/#override-request-validation-exceptions

Then you wont need the dependency and your endpoint can simply list the enum type like you do with name_valid_representation.

[vicente23]

Thanks for the explanation @jgould22.

I try to implement the example of the documentation, it works. I can easily customize the error message. To extract the first parameter that is invalid, I use the exc.errors()[0]['loc'][1]. Do you know a more efficient method ?

Here is the method that allows me to identify the invalid parameter:

@app.exception_handler(RequestValidationError)
async def validation_exception_handler(_request, exc):
    return PlainTextResponse(json.dumps({"message": f"The parameter {exc.errors()[0]['loc'][1]} is invalid"}), status_code=400)

Another way is to override the openapi documentation when starting the API by specifying the enum property for my parameter in the openapi.Json file. I get the expected result in the Swagger documentation. However, this is not ideal because I want to use pydantic and it is more difficult to maintain in my opinion.

Thanks!

[smarie]

I have the same issue than you, with all kind of usages of Enums. The Swagger UI autodoc always sets the dropdown menu as "disabled".

For example this :

from fastapi import FastAPI
from enum import Enum

app = FastAPI()

class Country(str, Enum):
    eu = "eu"
    us = "us"

@app.get("/")
def get_something(country: Country = Country.eu):
    return {"country": country.value}

This is the screenshot. You cannot see it but hovering over the dropdown leads my mouse icon to turn into a "forbidden" icon.

The same happens for the example in the doc : https://fastapi.tiangolo.com/tutorial/path-params/?h=enum#working-with-python-enumerations

I tried to do the same with an explicit Form(enum=...) but same result.

My versions:

• FastAPI: 0.94.1
• Uvicorn: 0.21.1
• Python: 3.9.6

[jgould22]

I have the same issue than you, with all kind of usages of Enums. The Swagger UI autodoc always sets the dropdown menu as "disabled".

It is not really the same issue, that is the behavior of swagger doc.

Just click "try it out" button the right side of that panel and it will unlock the field.

[smarie]

Indeed ! Oh, sorry for annoying you with such an obvious "problem". Thanks for the quick support !