From c1e1f38a274cd2eea07ebcfde955847733363383 Mon Sep 17 00:00:00 2001
From: Christian Cueni <christian.cueni@iterativ.ch>
Date: Wed, 24 Jul 2024 11:18:19 +0200
Subject: [PATCH] Optimize duedates in dashboards

---
 server/vbv_lernwelt/dashboard/views.py | 41 ++++++++------------------
 1 file changed, 12 insertions(+), 29 deletions(-)

diff --git a/server/vbv_lernwelt/dashboard/views.py b/server/vbv_lernwelt/dashboard/views.py
index e8266145..9d20bab7 100644
--- a/server/vbv_lernwelt/dashboard/views.py
+++ b/server/vbv_lernwelt/dashboard/views.py
@@ -306,45 +306,28 @@ def get_dashboard_due_dates(request):
         course_sessions = get_course_sessions_with_roles_for_user(request.user)
         course_session_ids = [cs.id for cs in course_sessions]
 
-        all_due_dates = DueDate.objects.filter(
-            course_session__id__in=course_session_ids
-        )
-
-        # filter only future due dates
-        due_dates = []
         today = date.today()
-        for due_date in all_due_dates:
-            # due_dates.append(due_date)
-            if due_date.end:
-                if due_date.end.date() >= today:
-                    due_dates.append(due_date)
-            elif due_date.start:
-                if due_date.start.date() >= today:
-                    due_dates.append(due_date)
 
-        due_dates.sort(key=lambda x: x.start)
-
-        # find course session by id in `course_sessions`
+        # Fetch future due dates in a single query using Q objects for complex filtering
+        future_due_dates = DueDate.objects.filter(
+            Q(course_session_id__in=course_session_ids),
+            Q(end__gte=today) | Q(start__gte=today)
+        ).select_related('course_session')
 
         result_due_dates = []
-        for due_date in due_dates:
-            data = DueDateSerializer(due_date).data
+        course_session_map = {cs.id: cs for cs in course_sessions}
+
+        for due_date in sorted(future_due_dates, key=lambda x: x.start):
+            data = DueDateSerializer(due_date).data
+            cs = course_session_map.get(due_date.course_session_id)
 
-            cs = next(
-                course_session
-                for course_session in course_sessions
-                if course_session.id == due_date.course_session.id
-            )
             if cs:
                 data["course_session"] = _create_course_session_dict(
                     cs, my_role=user_role(cs.roles), user_role=""
                 )
             result_due_dates.append(data)
 
-        return Response(
-            status=200,
-            data=result_due_dates,
-        )
+        return Response(status=200, data=result_due_dates)
 
     except PermissionDenied as e:
         raise e
@@ -625,7 +608,7 @@ def _get_course_sessions_with_roles_for_user(
         csr
         for csr in get_course_sessions_with_roles_for_user(user)
         if any(role in allowed_roles for role in csr.roles)
-        and csr.id in requested_cs_ids
+           and csr.id in requested_cs_ids
     ]  # noqa
 
     return all_cs_roles_for_user