Optimize exam list retrieval by consolidating queries and annotating candidate counts for improved performance

generic/views.py

@@ -1902,27 +1902,31 @@ class ExamViews(View, LoginRequiredMixin):
 
     @method_decorator(login_required)
     def exam_list(self, request, all=False, collection=None):
+        # Build a single queryset and annotate candidate counts to avoid per-item queries
         if collection is None:
             if not self.check_user_access(request.user):
-                # raise PermissionDenied
+                # Use a single queryset with Q to include authored or marked exams
-                exam_list = self.Exam.objects.filter(
-                    author__id=request.user.id, exam_mode=True
-                ).order_by("name")
-
-
-                exam_list = exam_list | self.Exam.objects.filter(
-                    markers__id=request.user.id, exam_mode=True
-                ).order_by("name")
-            else:
                 exam_list = (
-                    self.Exam.objects.prefetch_related(
+                    self.Exam.objects.filter(
-                        "valid_user_users", "valid_cid_users"
+                        (Q(author__id=request.user.id) | Q(markers__id=request.user.id)),
+                        exam_mode=True,
                     )
-                    .filter(exam_mode=True)
+                    .distinct()
                     .order_by("name")
                 )
             else:
-            exam_list = self.Exam.objects.filter(exam_mode=True, examcollection__in=[collection]).order_by("name")
+                exam_list = self.Exam.objects.filter(exam_mode=True).order_by("name")
+        else:
+            exam_list = (
+                self.Exam.objects.filter(exam_mode=True, examcollection__in=[collection])
+                .order_by("name")
+            )
+
+        # Annotate counts for template usage so `.count()` is not called per-object
+        exam_list = exam_list.annotate(
+            valid_cid_users_count=Count("valid_cid_users", filter=Q(valid_cid_users__active=True)),
+            valid_user_users_count=Count("valid_user_users", filter=Q(valid_user_users__is_active=True)),
+        ).select_related("examcollection").prefetch_related("author")
 
         if not all:
             exam_list = exam_list.filter(archive=False).order_by("name")