Performance optimizations

Close #107 (closed)

aleksis/apps/alsijil/model_extensions.py

 from datetime import date
-from typing import Dict, Optional, Union
+from typing import Dict, Optional, Union, Iterator
 
 from django.db.models import Exists, OuterRef, QuerySet
 from django.utils.translation import gettext as _
@@ -186,11 +186,12 @@ def get_or_create_lesson_documentation(
 
 
 @LessonPeriod.method
-def get_absences(self, week: Optional[CalendarWeek] = None) -> QuerySet:
+def get_absences(self, week: Optional[CalendarWeek] = None) -> Iterator:
     """Get all personal notes of absent persons for this lesson."""
     if not week:
         week = self.week
-    return self.personal_notes.filter(week=week.week, year=week.year, absent=True)
+
+    return filter(lambda p: p.week == week.week and p.year == week.year and p.absent, self.personal_notes.all())
 
 
 @LessonPeriod.method
@@ -230,7 +231,7 @@ def get_extra_marks(
         week = self.week
 
     stats = {}
-    for extra_mark in ExtraMark.objects.all():
+    for extra_mark in ExtraMark.all:
         qs = self.personal_notes.filter(
             week=week.week, year=week.year, extra_marks=extra_mark
         )