Support for MultiPart fields in OpenAPI docs and parsing

[adriangb]

Not sure if this is a bug report of feature request.

I would like to deserialize and document (in OpenAPI) a multipart request. The docs have an example, but it is not clear if the example is for an application/x-www-form-urlencoded request or a multipart/form-data request. From my testing (using requests, both content types / formats are accepted).

Additionally, the example gives me the following openapi.yaml:

paths:
    /something:
        post:
            responses: {}
            operationId: create_something
            parameters: []
            requestBody:
                content:
                    application/json:
                        schema:
                            nullable: false
                required: true

(side note, the spec requires that there always be at least 1 response documented)

The issue is that the content section incorrectly says application/json; I think it should be multipart/form-data or application/x-www-form-urlencoded.

If I replace SomethingInput with a Pydantic model, it at lest produces the right schema:

paths:
    /something:
        post:
            responses: {}
            operationId: create_something
            parameters: []
            requestBody:
                content:
                    application/json:
                        schema:
                            $ref: '#/components/schemas/SomethingInput'
                required: true

In this case all that would be missing for basic support is that the content type be fixed.

But for more advanced use cases, it would be nice to get:

1. Support for mixed files / json / other fields
2. Support for parsing out fields, e.g. if a field is a Pydantic model
3. Support for documenting the fields (including their content type, etc.) in the OpenAPI docs

For what it's worth, the way I handled this in my toy web framework project is to make the parameter to FromForm be required to be a Pydantic model and each field in the model represents a field in the multipart request. So something like:

class FieldModel(BaseModel):
    foo: str
    bar: int

class MultiPartModel(BaseModel):
    field_one: FromJson[FieldModel]
    field_two: FromFiles  # field_two is a file or files
    field_three: FromForm[...]  # allowing nested multipart/form-data or application/x-www-form-urlencoded


@post("/something")
async def create_something(input: FromForm[MultiPartModel]):
    ...

[RobertoPrevato]

This is definitely a bug - actually two bugs - thank you for reporting this. Just yesterday evening I published version 1.2.1 with several new features, I will add these two problems to the issues list.

[RobertoPrevato]

I just created two issues using the "Create issue from discussion" feature.

[adriangb]

glad to hear these are bugs and not unsupported features 😄

I just created two issues using the "Create issue from discussion" feature.

I didn't know that was a feature, but I see the button! That's cool.

[Franco-from-Owlish]

I am having an issue where the FromFiles field is a text field in the OpenAPI spec. Could an example be added to the OpenAPI section of the documentation for handling file uploads?