Returning an `Enum` from a `SerializerMethod`

[johnthagen]

Is it possible to express this:

class Item(Model):
    name = TextField()

@unique
class Color(Enum):
    Red = "red"
    Green = "green"
    Blue = "blue"


class ItemSerializer(ModelSerializer):
    color = SerializerMethodField()

    def get_color(self, instance) -> Color:
        return Color.Red.value

    class Meta:
        model = Item
        fields = "__all__"

We've been able to use Enums directly within Models, using https://github.com/akx/django-enumfields2 and that translates properly into an OpenAPI enum.

Is there a way to expose similar functionality through a SerializerMethod in a way drf-spectacular can process?

[johnthagen]

Interesting, this does seem to somewhat work, even though from looking at the code and they type hints on @extend_schema_field, I didn't see Enum so I was expecting this to not work?

_KnownPythonTypes = typing.Type[typing.Union[
    str, float, bool, bytes, int, dict, UUID, Decimal, datetime, date, time,
    timedelta, IPv4Address, IPv6Address,
]]

I guess I'd like to check that this is intended behavior 😄 .

Edit: This only partially seems to work.

[johnthagen]

So this seems to generate:

    Item:
      type: object
      properties:
        id:
          type: integer
          readOnly: true
        color:
          allOf:
          - $ref: '#/components/schemas/ColorEnum'
          readOnly: true
        name:
          type: string
      required:
      - color
      - id
      - name

... 

    ColorEnum:
      enum:
      - red
      - green
      - blue

But something is not correct because the Swagger UI shows:

And "ENUM_NAME_OVERRIDES" does not seem to work within drf-spectacular.

[johnthagen]

Switching to @extend_schema_field seems to produce the same result.

    @extend_schema_field(Color)
    def get_color(self, instance) -> Any:
        return Color.Red.value

[johnthagen]

I think what's causing the error is the

allOf:

line. My other EnumFields that work properly don't have that wrapping the $ref in the generated OpenAPI spec.

[johnthagen]

@tfranzel If there is a proper way to do this, I'm also happy to add a FAQ entry about it. 😃

[johnthagen]

Okay, not sure why I didn't think of this at first, but using an EnumField does make this work:

from enumfields.drf import EnumField

class Item(Model):
    name = TextField()

@unique
class Color(Enum):
    Red = "red"
    Green = "green"
    Blue = "blue"


class ItemSerializer(ModelSerializer):
    color = SerializerMethodField()

    @extend_schema_field(EnumField(Color))
    def get_color(self, instance) -> str:
        return Color.Red.value

    class Meta:
        model = Item
        fields = "__all__"

If this is indeed the proper way to do this, I'm happy to make an FAQ. Also, I could potentially see someone who doesn't use https://github.com/akx/django-enumfields2 wanting to export a simple Enum from a SerializerMethodField, so perhaps it's still worth a more generic solution within drf-spectacular?

Maybe natively supporting the StrEnum as one of the _KnownPythonTypes?

[johnthagen]

@tfranzel Any thoughts on this issue? I'm happy to open a PR describing whatever we think is the best solution (documenting that we support django-enumfields etc.). I wanted to make sure you didn't already have some "choices/enum-like" feature that exists for SerializerMethods.

[rvinzent]

@johnthagen I've got the same issue with the allOf wrapper on read only enums (and any other ref'd component), and ended up figuring out this is actually a correct schema for OpenAPI 3.0.x (source). In OpenAPI v3.1.x, we can apparently use JSON schema here which doesn't have these arbitrary restrictions. I don't think there's a bug here and what we'd really like is support for OpenAPI v3.1.x style referenced schemas because the generated clients choke on the allOf wrapper.

Turns out OpenAPI v3.1.0 is already supported. You just need to set OAS_VERSION: "3.1.0" in your settings. I've just tested against the latest python generated client and it seems to be working correctly