media type application/problem+json in additional responses

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.
• After submitting this, I commit to:
  • Read open issues with questions until I find 2 issues where I can help someone and add a comment to help there.
  • Or, I already hit the “watch” button in this repository to receive notifications and I commit to help at least 2 people that ask questions in the future.
  • Implement a Pull Request for a confirmed bug.

Example

Here’s a self-contained minimal, reproducible, example with my use case:

from fastapi import FastAPI
from fastapi.responses import JSONResponse
from pydantic import BaseModel

app = FastAPI()

class JsonApiResponse(JSONResponse):
    media_type = "application/vnd.api+json"

class JsonApiError(BaseModel):
    type: str
    title: str
    detail: str

@app.get(
    "/a/{id}",
    response_class=JsonApiResponse,
    responses={422: {
            "model": JsonApiError,
            "media_type": "application/problem+json"
        },
    },
)
async def a(id):
    pass  # pragma: no cover

Description

I would like to use a Pydantic model to specify an error message as conforming to application/problem+json, i.e. setting the media type to application/problem+json.

However, afaik, in the openAPI specification the media type is fixed to “application/json”, unless “response_class” is set with media_type as in the above example. However, this results in all responses having that media type.

The solution you would like

I would like to be able to set the media type individually for each response.

Describe alternatives you’ve considered

I propose that in the response dict’s the key “media_type” should be used to set the media type.

Naturally, if “media_type” is present it should take precedence over response_class which in turn overrides the default “application/json”.

@app.get(
    "/a/{id}",
    response_class=JsonApiResponse,
    responses={422: {
            "model": JsonApiError,
            "media_type": "application/problem+json"
        },
    },
)
async def a(id):
    pass  # pragma: no cover

I have not come up with any other ideas on how to solve this.

In case you find my proposal reasonable, I’d be happy to provide a pull request.

Environment

• OS: macOS
• FastAPI Version: 0.63.0
• Python version: 3.8.7

Additional context

[neveritt]

Such a solution generates the following for me:

"422": {
    "description": "Unprocessable Entity",
    "content": {
         "application/problem+json": {},
         "application/vnd.api+json": {
          "schema": {
              "$ref": "#/components/schemas/JsonApiError"
           }
        }
    }
}

While I am hoping to generate

"422": {
    "description": "Unprocessable Entity",
    "content": {
         "application/problem+json": {
          "schema": {
              "$ref": "#/components/schemas/JsonApiError"
           }
        }
    }
}

I’m pretty sure I could solve my problem by customizing the api as described in the doc though. However I was hoping for a more elegant solution

[github-actions[bot]]

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.