Fix N+1 query in event calendar found by sentry (#4104)

* Fix N+1 query in event calendar found by sentry

* isort

---------

Co-authored-by: Mira Weller <weller@rami.io>

src/pretix/base/services/quotas.py

@@ -29,6 +29,7 @@ from django.conf import settings
 from django.db import models
 from django.db.models import (
     Case, Count, F, Func, Max, OuterRef, Q, Subquery, Sum, Value, When,
+    prefetch_related_objects,
 )
 from django.utils.timezone import now
 
@@ -446,6 +447,7 @@ class QuotaAvailability:
                         self.results[q] = Quota.AVAILABILITY_RESERVED, 0
 
     def _compute_waitinglist(self, quotas, q_items, q_vars, size_left):
+        prefetch_related_objects(quotas, "event", "event__organizer")
         quotas = [
             q for q in quotas
             if not q.event.settings.waiting_list_auto_disable or q.event.settings.waiting_list_auto_disable.datetime(q.subevent or q.event) > now()

src/pretix/presale/views/organizer.py

@@ -561,6 +561,13 @@ def add_subevents_for_days(qs, before, after, ebd, timezones, event=None, cart_n
     for se in qs:
         if se.presale_is_running:
             quotas_to_compute += se.active_quotas
+            for q in se.active_quotas:
+                # save database lookups later
+                q.subevent = se
+                if event is not None:
+                    q.event = event
+                else:
+                    q.event = se.event
 
     qcache = {}
     if quotas_to_compute:
@@ -572,6 +579,8 @@ def add_subevents_for_days(qs, before, after, ebd, timezones, event=None, cart_n
     for se in qs:
         if qcache:
             se._quota_cache = qcache
+        if event is not None:  # save database lookup later
+            se.event = event
         kwargs = {'subevent': se.pk}
         if cart_namespace:
             kwargs['cart_namespace'] = cart_namespace