Support for Polymorphic Lists

[avere001]

I have tried this a few ways, but there seems to be no way to get polymorphic lists. For example, I can't find a way to document the content property of something like this:

{
  "type": "page",
  "content": [
    {
      "type": "article",
      "title": "...",
      "body": "..."
    },
    {
      "type": "image",
      "url": "...",
      "alt_text": "..."
    }
  ]
}

For me, the natural thing was to annotate the field with PolymorphicProxySerialzier(many=True, ...) but that doesn't work.

Is there any way to do this without using django-polymorphic / django-rest-polymorphic?

[tfranzel]

hi!

Is there any way to do this without using django-polymorphic / django-rest-polymorphic?

that is exactly the purpose of PolymorphicProxySerializer. it simulates what those libraries would do without having to use them. as a matter of fact you wouldn't use PolymorphicProxySerializer with those libraries, as instances of PolymorphicSerializer would get picked up automatically.

regarding your question. if the field is readOnly this is the easiest solution:

drf-spectacular/tests/test_polymorphic.py

Line 122 in 1f7cf5d

def test_polymorphic_serializer_as_method_field_via_extend_schema_field(no_warnings):

for read/write, you have to subclass the field and annotate that class. a pass will suffice as you just need something to attach the annotation to.

drf-spectacular/tests/test_polymorphic.py

Line 98 in 1f7cf5d

def test_polymorphic_serializer_as_field_via_extend_schema_field(no_warnings):

sidenote:
maybe we could extend extend_schema_serializer to additionally allow field overrides. that would eliminate that awkward annotation exercise. definitely something to look into.

[avere001]

Hi @tfranzel, thank you for the response.

The example you gave me only works when a single object is being returned, e.g.:

@extend_schema_field(
    PolymorphicProxySerializer(
        component_name='MetaPerson',
        serializers=[LegalPersonSerializer, NaturalPersonSerializer],
        resource_type_field_name='type',
    )
)
def get_field(self, request):
    return LegalPersonSerializer(...).data. # or NaturalPersonSerializer(...).data

What I want is the schema for a list of objects of varying types being returned such as below:

@extend_schema_field(
    PolymorphicProxySerializer(
        component_name='MetaPerson',
        serializers=[LegalPersonSerializer, NaturalPersonSerializer],
        resource_type_field_name='type',
        many=True,  # <--- This doesn't work
    )
)
def get_field(self, request):
    return [
        LegalPersonSerializer(...).data,
        NaturalPersonSerializer(...).data,
        ...
    ]

[greenled]

I'm looking for a solution to this problem too. For me, a PolymorphicProxySerialzier(many=True, ...) field, as mentioned by @avere001, would be the most natural API.

[tfranzel]

@avere001 now i get where you are coming from. this is indeed a missing feature.

now that i think of it there are ways to get PolymorphicProxySerialzier into "many mode" (via annotation of a viewsets's list) but there is currently no way to do it explicitly. certainly an unnecessary limitation.

good catch! i'll figure something out.

[avere001]

Cool, thank you @tfranzel!

[tfranzel]

please test if that fix works for you guys. cheers!

[avere001]

Just tested it and it is exactly what I was looking for. I appreciate your time on this, @tfranzel!

[unrealsolver]

@avere001 , do you have a full example for the usage? I am trying to do something very similar. Spectacular part is clear, but DRF is not.