Improve handling of child/parent groups

aleksis/apps/chronos/models.py

@@ -130,7 +130,7 @@ class LessonDataQuerySet(models.QuerySet):
         if isinstance(group, int):
             group = Group.objects.get(pk=group)
 
-        if group.parent_groups:
+        if group.parent_groups.all():
             # Prevent to show lessons multiple times
             return self.filter(Q(**{self._period_path + "lesson__groups": group}))
         else:
@@ -450,7 +450,7 @@ class Lesson(ExtensibleModel):
         return CalendarWeek(year=year, week=week)
 
     class Meta:
-        ordering = ["date_start"]
+        ordering = ["date_start", "subject"]
         indexes = [models.Index(fields=["date_start", "date_end"])]
 
 
@@ -559,7 +559,7 @@ class LessonPeriod(ExtensibleModel):
         )
 
     class Meta:
-        ordering = ["lesson__date_start", "period__weekday", "period__period"]
+        ordering = ["lesson__date_start", "period__weekday", "period__period", "lesson__subject"]
         indexes = [models.Index(fields=["lesson", "period"])]