Return union of Django objects

Hi,

Return an union of Django models isn’t supported at the moment (strawberry-graphql==0.74.1 and strawberry-graphql-django==0.2.5).

This example will fail:

Contributor = strawberry.union("Contributor", types=(Tenant, ShippingCompany))

    @strawberry_django.field
    def contributor(self) -> Optional[Contributor]:
        return getattr(self.contributor, "shippingcompany", self.contributor)

with this error:

The type "<class 'users.models.ShippingCompany'>" cannot be resolved for the field "contributor" , are you using a strawberry.field?

One workaround is to set _type_definition on the retuned type like this:

    @strawberry_django.field
    def contributor(self) -> Optional[Contributor]:
        if hasattr(self.contributor, "shippingcompany"):
            self.contributor.shippingcompany._type_definition = ShippingCompany._type_definition

            return self.contributor.shippingcompany

        self.contributor._type_definition = Tenant._type_definition  # type: ignore [attr-defined]

        return self.contributor

It would be great if we could return the Django objects directly.

[radix]

I’d just like to suggest that I think having a supported, explicit mechanism to choose the variant, unrelated to any Django support, would be useful as the first solution to this problem (I assume _type_definition is a private member). If we can return an object that includes both the value and the chosen variant, then an automatic variant inference could be built on top of that.

[jkimbo]

@patrick91 no, I was thinking that you could implement some logic in the strawberry-django resolver to look up the right StrawberryType from the Django instance. Something like this:

class StrawberryDjangoField(StrawberryField):
	def get_result(self, source, info, arguments):
		if self.resolved_type is Union:
			model_instance = super.get_result(source, info, arguments)
			strawberry_type = get_type_from_instance(model_instance, options=self.resolved_type.types)  # this function will need to be implemented
			return strawberry_type.from_instance(model_instance)
		...

What do you think?