From 1481111dca41875410e21545bcddab3be299bdc0 Mon Sep 17 00:00:00 2001
From: "T. Franzel" <tfranzel@users.noreply.github.com>
Date: Fri, 21 Jul 2023 21:14:00 +0200
Subject: [PATCH] fix django-polymorphic empty serializer case #1029 #542

---
 drf_spectacular/contrib/rest_polymorphic.py | 29 ++++++++++++---------
 tests/contrib/test_rest_polymorphic.py      |  7 +++++
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/drf_spectacular/contrib/rest_polymorphic.py b/drf_spectacular/contrib/rest_polymorphic.py
index 3505ffc3..431fb974 100644
--- a/drf_spectacular/contrib/rest_polymorphic.py
+++ b/drf_spectacular/contrib/rest_polymorphic.py
@@ -20,7 +20,12 @@ def map_serializer(self, auto_schema, direction):
             resource_type = serializer.to_resource_type(sub_model)
             component = auto_schema.resolve_serializer(sub_serializer, direction)
             if not component:
-                continue
+                # rebuild a virtual schema-less component to model empty serializers
+                component = ResolvedComponent(
+                    name=auto_schema._get_serializer_name(sub_serializer, direction),
+                    type=ResolvedComponent.SCHEMA,
+                    object='virtual'
+                )
             typed_component = self.build_typed_component(
                 auto_schema=auto_schema,
                 component=component,
@@ -49,21 +54,21 @@ def build_typed_component(self, auto_schema, component, resource_type_field_name
         else:
             typed_component_name = f'{component.name}Typed'
 
+        resource_type_schema = build_object_type(
+            properties={resource_type_field_name: build_basic_type(OpenApiTypes.STR)},
+            required=None if patched else [resource_type_field_name]
+        )
+        # if sub-serializer has an empty schema, only expose the resource_type field part
+        if component.schema:
+            schema = {'allOf': [resource_type_schema, component.ref]}
+        else:
+            schema = resource_type_schema
+
         component_typed = ResolvedComponent(
             name=typed_component_name,
             type=ResolvedComponent.SCHEMA,
             object=component.object,
-            schema={
-                'allOf': [
-                    build_object_type(
-                        properties={
-                            resource_type_field_name: build_basic_type(OpenApiTypes.STR)
-                        },
-                        required=None if patched else [resource_type_field_name]
-                    ),
-                    component.ref,
-                ]
-            }
+            schema=schema,
         )
         auto_schema.registry.register_on_missing(component_typed)
         return component_typed
diff --git a/tests/contrib/test_rest_polymorphic.py b/tests/contrib/test_rest_polymorphic.py
index 0d35433f..4c5221a6 100644
--- a/tests/contrib/test_rest_polymorphic.py
+++ b/tests/contrib/test_rest_polymorphic.py
@@ -113,10 +113,17 @@ def test_rest_polymorphic_split_request_with_ro_serializer(no_warnings):
     assert components['PersonRequest']['oneOf'] == [
         {'$ref': '#/components/schemas/LegalPersonTypedRequest'},
         {'$ref': '#/components/schemas/NaturalPersonTypedRequest'},
+        {'$ref': '#/components/schemas/NomadicPersonTypedRequest'},
     ]
     assert components['PersonRequest']['discriminator']['mapping'] == {
         'legal': '#/components/schemas/LegalPersonTypedRequest',
         'natural': '#/components/schemas/NaturalPersonTypedRequest',
+        'nomadic': '#/components/schemas/NomadicPersonTypedRequest',
+    }
+    assert components['NomadicPersonTypedRequest'] == {
+        'properties': {'resourcetype': {'type': 'string'}},
+        'required': ['resourcetype'],
+        'type': 'object',
     }