Optimize submissions frontend queries

backend/api/context.py

@@ -4,15 +4,12 @@
 from django.http.request import HttpRequest
 from strawberry.types import Info as StrawberryInfo
 
-from voting.models.vote import Vote
-
 
 @dataclass
 class Context:
     request: HttpRequest
     response: Any
     _user_can_vote: bool | None = None
-    _my_votes: dict[int, Vote] | None = None
 
 
 type Info = StrawberryInfo[Context, Any]

backend/api/submissions/schema.py

@@ -2,14 +2,14 @@
 
 import strawberry
 import strawberry_django
+from django.db.models import Case, IntegerField, When
 
 from api.context import Info
 from api.permissions import CanSeeSubmissions, IsAuthenticated
 from api.submissions.permissions import CanSeeSubmissionRestrictedFields
 from api.types import Paginated
 from conferences import models as conference_models
 from submissions import models as submission_models
-from voting import models as voting_models
 from voting.helpers import check_if_user_can_vote
 
 from .types import Submission, SubmissionTag
@@ -72,14 +72,7 @@ def submissions(
         ):
             raise PermissionError("You need to have a ticket to see submissions")
 
-        qs = conference.submissions.prefetch_related(
-            "type",
-            "duration",
-            "schedule_items",
-            "languages",
-            "audience_level",
-            "tags",
-        )
+        qs = conference.submissions.all()
 
         if only_accepted:
             qs = qs.filter(status=submission_models.Submission.STATUS.accepted)
@@ -103,21 +96,31 @@ def submissions(
         if audience_levels:
             qs = qs.filter(audience_level__id__in=audience_levels)
 
-        qs = qs.order_by("id").distinct()
-
-        all_submissions = list(qs)
-        random.Random(user.id).shuffle(all_submissions)
-
-        total_items = len(all_submissions)
-        submissions = list(all_submissions[(page - 1) * page_size : page * page_size])
-
-        info.context._my_votes = {
-            vote.submission_id: vote
-            for vote in voting_models.Vote.objects.filter(
-                user_id=user.id,
-                submission__in=submissions,
+        submission_ids = list(
+            qs.order_by("id").distinct().values_list("id", flat=True)
+        )
+        random.Random(user.id).shuffle(submission_ids)
+
+        total_items = len(submission_ids)
+        page_submission_ids = submission_ids[
+            (page - 1) * page_size : page * page_size
+        ]
+        submissions = conference.submissions.filter(id__in=page_submission_ids)
+        if not only_accepted:
+            # This relation is used by a permission check, so it is invisible to
+            # Strawberry Django's selection-based optimizer.
+            submissions = submissions.prefetch_related("schedule_items")
+
+        if page_submission_ids:
+            submissions = submissions.order_by(
+                Case(
+                    *(
+                        When(id=submission_id, then=position)
+                        for position, submission_id in enumerate(page_submission_ids)
+                    ),
+                    output_field=IntegerField(),
+                )
             )
-        }
 
         return Paginated.paginate_list(
             items=submissions,

backend/api/submissions/tests/test_frontend_queries.py

@@ -113,7 +113,7 @@
 
 @pytest.mark.parametrize(
     ("submission_count", "expected_queries"),
-    [(1, 16), (4, 19)],
+    [(1, 14), (4, 14)],
 )
 def test_voting_submissions_frontend_query(
     graphql_client,
@@ -148,7 +148,7 @@ def test_voting_submissions_frontend_query(
 
 @pytest.mark.parametrize(
     ("submission_count", "expected_queries"),
-    [(1, 12), (4, 21)],
+    [(1, 6), (4, 6)],
 )
 def test_dynamic_content_proposals_frontend_query(
     graphql_client,

backend/api/submissions/types.py

@@ -2,6 +2,7 @@
 
 import strawberry
 import strawberry_django
+from django.db.models import Prefetch
 from strawberry.types import Info
 from strawberry.types.field import StrawberryField
 
@@ -181,28 +182,34 @@ def id(self, info: Info) -> strawberry.ID:
     def can_edit(self, info: Info) -> bool:
         return self.can_edit(info.context.request)
 
-    @strawberry.field
+    @strawberry_django.field(
+        prefetch_related=lambda info: Prefetch(
+            "votes",
+            queryset=(
+                voting_models.Vote.objects.filter(
+                    user_id=info.context.request.user.id,
+                )
+                if info.context.request.user.is_authenticated
+                else voting_models.Vote.objects.none()
+            ),
+        )
+    )
     def my_vote(self, info: Info) -> VoteType | None:
         request = info.context.request
 
         if not request.user.is_authenticated:
             return None
 
-        if info.context._my_votes is not None:
-            return info.context._my_votes.get(self.id)
-
-        try:
-            return self.votes.get(user_id=request.user.id)
-        except voting_models.Vote.DoesNotExist:
-            return None
+        return next(
+            (vote for vote in self.votes.all() if vote.user_id == request.user.id),
+            None,
+        )
 
     @strawberry_django.field(prefetch_related=["languages"])
     def languages(self, info: Info) -> list[Language] | None:
         return list(self.languages.all())
 
-    @strawberry_django.field
-    def tags(self, info: Info) -> list[SubmissionTag] | None:
-        return self.tags.all()
+    tags: list[SubmissionTag] | None = strawberry_django.field()
 
     @strawberry_django.field
     def materials(self) -> list[ProposalMaterial]:

backend/schema.graphql

@@ -1459,6 +1459,7 @@ type Submission {
   notes: String
   doNotRecord: Boolean
   scheduleItems: [ScheduleItem!]!
+  tags: [SubmissionTag!]
   multilingualElevatorPitch: MultiLingualString
   multilingualAbstract: MultiLingualString
   multilingualTitle: MultiLingualString
@@ -1469,7 +1470,6 @@ type Submission {
   canEdit: Boolean!
   myVote: VoteType
   languages: [Language!]
-  tags: [SubmissionTag!]
   materials: [ProposalMaterial!]!
 }