dnscms: prefetch and select related when quering future events

dnscms/events/models.py

@@ -1,7 +1,7 @@
 from django import forms
 from django.core.exceptions import ValidationError
 from django.db import models
-from django.db.models import Min, Q, UniqueConstraint
+from django.db.models import Min, Prefetch, Q, UniqueConstraint
 from django.utils import timezone
 from django.utils.html import mark_safe
 from django.utils.translation import gettext_lazy as _
@@ -45,7 +45,23 @@ class EventIndex(HeadlessMixin, Page):
     subpage_types = ["events.EventPage"]
 
     def future_events(self, info, **kwargs):
-        return EventPage.objects.live().future().order_by("next_occurrence")
+        return (
+            EventPage.objects.live()
+            .future()
+            .order_by("next_occurrence")
+            .select_related("featured_image")
+            .prefetch_related(
+                Prefetch(
+                    "occurrences",
+                    queryset=EventOccurrence.objects.select_related("venue"),
+                ),
+                "categories",
+                Prefetch(
+                    "organizers",
+                    queryset=EventOrganizer.objects.select_related("association"),
+                ),
+            )
+        )
 
     graphql_fields = [
         GraphQLCollection(

dnscms/tests/test_events.py

@@ -2,6 +2,8 @@ from datetime import datetime, timedelta
 
 import pytest
 from django.core.exceptions import ValidationError
+from django.db import connection
+from django.test.utils import CaptureQueriesContext
 from django.utils import timezone
 
 from events.admin import EventDateColumn, OrganizersColumn
@@ -188,6 +190,64 @@ def test_graphql_event_index_future_events_query(event_index, graphql_post):
     assert "Upcoming gig" in titles
 
 
+def test_future_events_does_not_have_n_plus_one_queries(
+    event_index, venue, association_index, graphql_post
+):
+    """Regression test: query count for futureEvents stays bounded as events grow."""
+    konsert = EventCategory.objects.create(name="Konsert", slug="konsert")
+    association = AssociationPageFactory(parent=association_index, title="DNS")
+    org = EventOrganizer.objects.create(name="Forening", slug="forening", association=association)
+    image = CustomImageFactory(title="Cover")
+    now = timezone.now()
+
+    for i in range(5):
+        event = EventPageFactory(
+            parent=event_index,
+            title=f"Event {i}",
+            body=[("paragraph", "<p>x</p>")],
+            featured_image=image,
+        )
+        event.categories.add(konsert)
+        EventOrganizerLink.objects.create(event=event, organizer=org)
+        EventOccurrence.objects.create(
+            event=event,
+            start=now + timedelta(days=i + 1),
+            venue=venue,
+        )
+
+    home_query = """
+        query {
+          eventIndex {
+            futureEvents {
+              id
+              title
+              subtitle
+              body { blockType }
+              featuredImage { url }
+              occurrences { start end venueCustom venue { title } }
+              categories { name slug }
+              organizers { name slug association { title } }
+            }
+          }
+        }
+    """
+
+    with CaptureQueriesContext(connection) as ctx:
+        response, body = graphql_post(home_query)
+
+    assert response.status_code == 200
+    assert "errors" not in body, body
+    assert len(body["data"]["eventIndex"]["futureEvents"]) == 5
+
+    # Bump only alongside an intentional resolver change.
+    max_queries = 6
+    assert len(ctx) <= max_queries, (
+        f"futureEvents took {len(ctx)} queries for 5 events — likely N+1. "
+        f"Captured queries:\n"
+        + "\n".join(f"  {i + 1}. {q['sql'][:120]}" for i, q in enumerate(ctx.captured_queries))
+    )
+
+
 def test_graphql_event_index_future_events_ordered_by_next_occurrence(event_index, graphql_post):
     now = timezone.now()