minimal simplification

jdav_web/members/models.py

@@ -1282,10 +1282,10 @@ class Freizeit(CommonModel):
     @property
     def total_seminar_days(self):
         """calculate seminar days based on intervention hours in every day"""
+        # TODO: add tests for this
         if hasattr(self, 'ljpproposal'):
             hours_per_day = (
-                Intervention.objects
-                .filter(ljp_proposal_id=self.ljpproposal.id)
+                self.ljpproposal.intervention_set
                 .annotate(day=TruncDate('date_start'))  # Extract the date (without time)
                 .values('day')  # Group by day
                 .annotate(total_duration=Sum('duration'))  # Sum durations for each day