Fix AttributeError when using optimizer and prefetch_related (#533)

* Add a test capturing the failure

* Short-circuit when a queryset has been sliced

There are several places in the codebase where qs._result_cache is evaluated.

If a QuerySet has been sliced (e.g., prefetched with pagination in DjangoOptimizerExtension), it has been evaluated as a list and will not have the `_result_cache` attrib.

* Update test to verify short-circuiting works as expected

strawberry_django/optimizer.py

@@ -694,6 +694,10 @@ def optimize(
  if isinstance(qs, BaseManager):
  qs = cast(QuerySet[_M], qs.all())
 
+ if isinstance(qs, list):
+ # return sliced queryset as-is
+ return qs
+
  # Avoid optimizing twice and also modify an already resolved queryset
  if (
  get_queryset_config(qs).optimized or qs._result_cache is not None # type: ignore

strawberry_django/permissions.py

@@ -108,6 +108,10 @@ def filter_with_perms(qs: QuerySet[_M], info: Info) -> QuerySet[_M]:
  if not context.checkers or context.is_safe:
  return qs
 
+ if isinstance(qs, list):
+ # return sliced queryset as-is
+ return qs
+
  # Do not do anything is results are cached
  if qs._result_cache is not None: # type: ignore
  set_perm_safe(False)

strawberry_django/resolvers.py

@@ -27,6 +27,10 @@
 
 
 def default_qs_hook(qs: models.QuerySet[_M]) -> models.QuerySet[_M]:
+ if isinstance(qs, list):
+ # return sliced queryset as-is
+ return qs
+
  # FIXME: We probably won't need this anymore when we can use graphql-core 3.3.0+
  # as its `complete_list_value` gives a preference to async iteration it if is
  # provided by the object.

tests/test_optimizer.py

@@ -1025,3 +1025,82 @@ def test_query_nested_connection_with_filter(db, gql_client: GraphQLTestClient):
  assert {
  edge["node"]["id"] for edge in result["issuesWithFilters"]["edges"]
  } == expected
+
+
+@pytest.mark.django_db(transaction=True)
+def test_query_with_optimizer_paginated_prefetch():
+ @strawberry_django.type(Milestone, pagination=True)
+ class MilestoneTypeWithNestedPrefetch:
+ @strawberry_django.field()
+ def name(self, info) -> str:
+ return self.name
+
+ @strawberry_django.type(
+ Project,
+ )
+ class ProjectTypeWithPrefetch:
+ @strawberry_django.field()
+ def name(self, info) -> str:
+ return self.name
+
+ milestones: List[MilestoneTypeWithNestedPrefetch]
+
+ milestone1 = MilestoneFactory.create()
+ project = milestone1.project
+ MilestoneFactory.create(project=project)
+
+ @strawberry.type
+ class Query:
+ projects: List[ProjectTypeWithPrefetch] = strawberry_django.field()
+
+ query1 = utils.generate_query(Query, enable_optimizer=False)
+ query_str = """
+ query TestQuery {
+ projects {
+ name
+ milestones (pagination: {limit: 1}) {
+ name
+ }
+ }
+ }
+ """
+
+ # NOTE: The following assertion doesn't work because the
+ # DjangoOptimizerExtension instance is not the one within the
+ # generate_query wrapper
+ """
+ assert DjangoOptimizerExtension.enabled.get()
+ """
+ result1 = query1(query_str)
+
+ assert isinstance(result1, ExecutionResult)
+ assert not result1.errors
+ assert result1.data == {
+ "projects": [
+ {
+ "name": project.name,
+ "milestones": [
+ {
+ "name": milestone1.name,
+ },
+ ],
+ },
+ ],
+ }
+
+ query2 = utils.generate_query(Query, enable_optimizer=True)
+ result2 = query2(query_str)
+
+ assert isinstance(result2, ExecutionResult)
+ assert result2.data == {
+ "projects": [
+ {
+ "name": project.name,
+ "milestones": [
+ {
+ "name": milestone1.name,
+ },
+ ],
+ },
+ ],
+ }