Test optimizer with polymorphic relay node

strawberry_django/optimizer.py

@@ -843,7 +843,7 @@ def _get_model_hints_from_connection(
             schema,
             get_object_definition(e_type, strict=True),
         )
-        assert isinstance(e_gql_definition, GraphQLObjectType)
+        assert isinstance(e_gql_definition, (GraphQLObjectType, GraphQLInterfaceType))
         e_info = _generate_selection_resolve_info(
             info,
             edges,
@@ -856,7 +856,10 @@ def _get_model_hints_from_connection(
                 continue
 
             n_gql_definition = _get_gql_definition(schema, n_definition)
-            assert isinstance(n_gql_definition, GraphQLObjectType)
+            assert isinstance(
+                n_gql_definition,
+                (GraphQLObjectType, GraphQLInterfaceType),
+            )
             n_info = _generate_selection_resolve_info(
                 info,
                 nodes,

tests/node_polymorphism/models.py

@@ -0,0 +1,14 @@
+from django.db import models
+from polymorphic.models import PolymorphicModel
+
+
+class Project(PolymorphicModel):
+    topic = models.CharField(max_length=30)
+
+
+class ArtProject(Project):
+    artist = models.CharField(max_length=30)
+
+
+class ResearchProject(Project):
+    supervisor = models.CharField(max_length=30)

tests/node_polymorphism/schema.py

@@ -0,0 +1,35 @@
+
+import strawberry
+from strawberry.relay import ListConnection
+
+import strawberry_django
+from strawberry_django.optimizer import DjangoOptimizerExtension
+
+from .models import ArtProject, Project, ResearchProject
+
+
+@strawberry_django.interface(Project)
+class ProjectType(strawberry.relay.Node):
+    topic: strawberry.auto
+
+
+@strawberry_django.type(ArtProject)
+class ArtProjectType(ProjectType):
+    artist: strawberry.auto
+
+
+@strawberry_django.type(ResearchProject)
+class ResearchProjectType(ProjectType):
+    supervisor: strawberry.auto
+
+
+@strawberry.type
+class Query:
+    projects: ListConnection[ProjectType] = strawberry_django.connection()
+
+
+schema = strawberry.Schema(
+    query=Query,
+    types=[ArtProjectType, ResearchProjectType],
+    extensions=[DjangoOptimizerExtension],
+)

tests/node_polymorphism/test_optimizer.py

@@ -0,0 +1,52 @@
+import pytest
+
+from .models import ArtProject, ResearchProject
+from .schema import schema
+
+
+@pytest.mark.django_db(transaction=True)
+def test_polymorphic_interface_query():
+    ap = ArtProject.objects.create(topic="Art", artist="Artist")
+    rp = ResearchProject.objects.create(topic="Research", supervisor="Supervisor")
+
+    query = """\
+    query {
+      projects {
+        edges {
+          node {
+            __typename
+            topic
+            ... on ArtProjectType {
+              artist
+            }
+            ... on ResearchProjectType {
+              supervisor
+            }
+          }
+        }
+      }
+    }
+    """
+
+    result = schema.execute_sync(query)
+    assert not result.errors
+    assert result.data == {
+        "projects": {
+            "edges": [
+                {
+                    "node": {
+                        "__typename": "ArtProjectType",
+                        "topic": ap.topic,
+                        "artist": ap.artist,
+                    }
+                },
+                {
+                    "node": {
+                        "__typename": "ResearchProjectType",
+                        "topic": rp.topic,
+                        "supervisor": rp.supervisor,
+                    }
+                },
+            ]
+        }
+    }