Type annotating a recursive serializer

[johnthagen]

I'd like to model the following type:

class ItemSerializer(ModelSerializer):
    children = ItemSerializer(many=True)

Due to Python limitations with how classes are defined this is not possible.

I thought about looking at https://github.com/heywbj/django-rest-framework-recursive, but this hasn't been updated for 5 years and there are reports about it not working with modern Django versions:

• Not working in django 4 heywbj/django-rest-framework-recursive#35

Finally, I thought of trying a SerializerMethod like:

class ItemSerializer(ModelSerializer):
    children = SerializerMethodField()

    def get_children(self, instance: Item) -> list[Item]:
        children = instance...
        return ItemSerializer(children, many=True).data

But type hints containing Model subclasses don't seem to be supported, which makes sense.

I was curious if there was some other way to get a nested serializer to be registered/recognized with drf-spectacular.

[johnthagen]

Interesting, using the Serializer as a type hint seems to work:

from __future__ import annotations

class ItemSerializer(ModelSerializer):
    children = SerializerMethodField()

    def get_children(self, instance: Item) -> ItemSerializer:
        children = instance...
        return ItemSerializer(children, many=True).data

Looks like this is documented here:

• https://drf-spectacular.readthedocs.io/en/latest/customization.html#step-3-extend-schema-field-and-type-hints

It takes either basic types or a Serializer as argument. In case of basic types (e.g. str, int, etc.) a type hint is already sufficient.

It might be more discoverable if the opening page that lists SerializerMethodField (https://drf-spectacular.readthedocs.io/en/latest/readme.html) linked to this subsection.