Support the Node interface

example_project/app/schema.py

@@ -43,6 +43,8 @@
 
 
 class Query(graphene.ObjectType):
+    node = relay.Node.Field()
+
     all_postal_codes = DjangoListField(PostalCodeType)
     all_developers = DjangoListField(DeveloperType)
     all_property_managers = DjangoListField(PropertyManagerType)

query_optimizer/ast.py

@@ -7,7 +7,7 @@
 from django.db.models import Field, ForeignKey, Model
 from graphene import Connection, ObjectType, PageInfo
 from graphene.relay.node import AbstractNode
-from graphene.types.definitions import GrapheneObjectType, GrapheneUnionType
+from graphene.types.definitions import GrapheneInterfaceType, GrapheneObjectType, GrapheneUnionType
 from graphene.utils.str_converters import to_snake_case
 from graphene_django import DjangoObjectType
 from graphql import (
@@ -16,6 +16,7 @@
     FragmentSpreadNode,
     GraphQLField,
     GraphQLOutputType,
+    GraphQLSchema,
     InlineFragmentNode,
     SelectionNode,
 )
@@ -182,14 +183,17 @@ def handle_fragment_spread(self, field_type: GrapheneObjectType, fragment_spread
         selections = get_selections(fragment_definition)
         return self.handle_selections(field_type, selections)
 
-    def handle_inline_fragment(self, field_type: GrapheneUnionType, inline_fragment: InlineFragmentNode) -> None:
-        fragment_type = get_fragment_type(field_type, inline_fragment)
+    def handle_inline_fragment(
+        self,
+        field_type: GrapheneUnionType | GrapheneInterfaceType,
+        inline_fragment: InlineFragmentNode,
+    ) -> None:
+        fragment_type = get_fragment_type(field_type, inline_fragment, self.info.schema)
         fragment_model: type[Model] = fragment_type.graphene_type._meta.model
-        if fragment_model != self.model:
-            return None
-
-        selections = get_selections(inline_fragment)
-        return self.handle_selections(fragment_type, selections)
+        if fragment_model == self.model:
+            selections = get_selections(inline_fragment)
+            return self.handle_selections(fragment_type, selections)
+        return None
 
     def get_graphene_type(self, field_type: GrapheneObjectType, field_node: FieldNode) -> GrapheneType:
         graphql_field = get_field_def(self.info.schema, field_type, field_node)
@@ -266,14 +270,27 @@ def is_to_one(field: Field) -> TypeGuard[ToOneField]:
     return bool(field.many_to_one or field.one_to_one)
 
 
-def get_fragment_type(field_type: GrapheneUnionType, inline_fragment: InlineFragmentNode) -> GrapheneObjectType:
+def get_fragment_type(
+    field_type: GrapheneUnionType | GrapheneInterfaceType,
+    inline_fragment: InlineFragmentNode,
+    schema: GraphQLSchema,
+) -> GrapheneObjectType:
     fragment_type_name = inline_fragment.type_condition.name.value
-    gen = (t for t in field_type.types if t.name == fragment_type_name)
-    fragment_type: Optional[GrapheneObjectType] = next(gen, None)
 
-    if fragment_type is None:  # pragma: no cover
-        msg = f"Fragment type '{fragment_type_name}' not found in union '{field_type}'"
-        raise OptimizerError(msg)
+    # For unions, fetch the type from in the union.
+    if isinstance(field_type, GrapheneUnionType):
+        gen = (t for t in field_type.types if t.name == fragment_type_name)
+        fragment_type: Optional[GrapheneObjectType] = next(gen, None)
+        if fragment_type is None:  # pragma: no cover
+            msg = f"Fragment type '{fragment_type_name}' not found in union '{field_type}'"
+            raise OptimizerError(msg)
+
+    # For interfaces, fetch the type from in the schema.
+    else:
+        fragment_type: Optional[GrapheneObjectType] = schema.get_type(fragment_type_name)
+        if fragment_type is None:  # pragma: no cover
+            msg = f"Fragment type '{fragment_type_name}' not found in schema."
+            raise OptimizerError(msg)
 
     return fragment_type
 

tests/test_relay_node.py

@@ -10,6 +10,36 @@
 ]
 
 
+def test_relay__global_node(graphql_client):
+    apartment = ApartmentFactory.create(building__name="1")
+    global_id = to_global_id(str(ApartmentNode), apartment.pk)
+
+    query = """
+        query {
+          node(id: "%s") {
+            ... on ApartmentNode {
+              building {
+                name
+              }
+            }
+          }
+        }
+    """ % (global_id,)
+
+    response = graphql_client(query)
+    assert response.no_errors, response.errors
+
+    # 1 query for fetching apartment and related buildings
+    assert response.queries.count == 1, response.queries.log
+
+    assert response.queries[0] == has(
+        'FROM "app_apartment"',
+        'INNER JOIN "app_building"',
+    )
+
+    assert response.content == {"building": {"name": "1"}}
+
+
 def test_relay__node(graphql_client):
     apartment = ApartmentFactory.create(building__name="1")
     global_id = to_global_id(str(ApartmentNode), apartment.pk)
@@ -32,6 +62,7 @@ def test_relay__node(graphql_client):
 
     assert response.queries[0] == has(
         'FROM "app_apartment"',
+        'INNER JOIN "app_building"',
     )
 
     assert response.content == {"building": {"name": "1"}}