From 2828132264afc4131facdc80fc4f5b5b80f862b0 Mon Sep 17 00:00:00 2001
From: Glenn Matthews <glenn.matthews@networktocode.com>
Date: Fri, 3 Mar 2023 09:24:57 -0500
Subject: [PATCH] Add option to provide a callable for
 PolymorphicProxySerializer.serializers

---
 drf_spectacular/utils.py  | 20 +++++++++++++++++++-
 tests/test_polymorphic.py | 21 ++++++++++++++++++++-
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/drf_spectacular/utils.py b/drf_spectacular/utils.py
index 03b52b4b..c795b0f1 100644
--- a/drf_spectacular/utils.py
+++ b/drf_spectacular/utils.py
@@ -64,11 +64,19 @@ def create(self, request, *args, **kwargs):
     *drf-spectacular* processes the serializer. In those cases you can explicitly state
     the mapping with ``{'legal': LegalPersonSerializer, ...}``, but it is then your
     responsibility to have a valid mapping.
+
+    It is also permissible to provide a callable with no parameters for ``serializers``,
+    such as a lambda that will return an appropriate list or dict when evaluated.
     """
     def __init__(
             self,
             component_name: str,
-            serializers: Union[Sequence[_SerializerType], Dict[str, _SerializerType]],
+            serializers: Union[
+                Sequence[_SerializerType],
+                Dict[str, _SerializerType],
+                Callable[[], Sequence[_SerializerType]],
+                Callable[[], Dict[str, _SerializerType]]
+            ],
             resource_type_field_name: Optional[str],
             many: Optional[bool] = None,
     ):
@@ -88,6 +96,16 @@ def __new__(cls, *args, **kwargs):
         instance._many = many
         return instance
 
+    @property
+    def serializers(self):
+        if callable(self._serializers):
+            self._serializers = self._serializers()
+        return self._serializers
+
+    @serializers.setter
+    def serializers(self, value):
+        self._serializers = value
+
     @property
     def data(self):
         self._trap()
diff --git a/tests/test_polymorphic.py b/tests/test_polymorphic.py
index 22e63298..2f5665cf 100644
--- a/tests/test_polymorphic.py
+++ b/tests/test_polymorphic.py
@@ -93,8 +93,27 @@ def create(self, request, *args, **kwargs):
         def partial_update(self, request, *args, **kwargs):
             return Response({})  # pragma: no cover
 
+    lambda_poly_proxy = PolymorphicProxySerializer(
+        component_name='MetaPerson',
+        serializers=lambda: [LegalPersonSerializer, NaturalPersonSerializer],
+        resource_type_field_name='type',
+    )
+
+    class LambdaPersonViewSet(viewsets.GenericViewSet):
+        @extend_schema(request=lambda_poly_proxy, responses=lambda_poly_proxy)
+        def create(self, request, *args, **kwargs):
+            return Response({})  # pragma: no cover
+
+        @extend_schema(
+            request=lambda_poly_proxy,
+            responses=lambda_poly_proxy,
+            parameters=[OpenApiParameter('id', int, OpenApiParameter.PATH)],
+        )
+        def partial_update(self, request, *args, **kwargs):
+            return Response({})  # pragma: no cover
+
 
-@pytest.mark.parametrize('viewset', [ImplicitPersonViewSet, ExplicitPersonViewSet])
+@pytest.mark.parametrize('viewset', [ImplicitPersonViewSet, ExplicitPersonViewSet, LambdaPersonViewSet])
 def test_polymorphic(no_warnings, viewset):
     assert_schema(
         generate_schema('persons', viewset),