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sheets/models.py

@@ -1,7 +1,10 @@
 from django.db import models
 from django.utils import timezone
 from django.core.validators import MinValueValidator, MaxValueValidator  
-
+from decimal import Decimal
+from django.db.models import Sum
+from django.db.models.functions import Coalesce
+from django.db.models import DecimalField, Value
 class Institute(models.Model):
     name = models.CharField(max_length=100)
     
@@ -73,8 +76,7 @@ class CellReference(models.Model):
     class Meta:
         unique_together = ['source_cell', 'target_cell']
 
-from decimal import Decimal
-from django.db import models
+
 
 class Betriebskosten(models.Model):
     KOSTENTYP_CHOICES = [
@@ -263,10 +265,7 @@ class BetriebskostenSummary(models.Model):
     umlage_personal = models.DecimalField(max_digits=12, decimal_places=2, default=0)
 
     def recalculate(self):
-        from django.db.models import Sum
-        from django.db.models.functions import Coalesce
-        from django.db.models import DecimalField, Value
-        from .models import Betriebskosten
+   
 
         items = Betriebskosten.objects.all()
 
@@ -291,7 +290,7 @@ class BetriebskostenSummary(models.Model):
         self.save()
 
 # models.py
-from django.db import models
+
 
 class AbrechnungCell(models.Model):
     """