update

sheets/models.py

@@ -3,6 +3,29 @@ from django.utils import timezone
 from django.core.validators import MinValueValidator, MaxValueValidator  
 
 
+class Betriebskosten(models.Model):
+    KOSTENTYP_CHOICES = [
+        ('sach', 'Sachkostöen'),
+        ('ln2', 'LN2'),
+        ('helium', 'Helium'),
+        ('inv', 'Inventar'),
+    ]
+    
+    buchungsdatum = models.DateField('Buchungsdatum')
+    rechnungsnummer = models.CharField('Rechnungsnummer', max_length=50)
+    kostentyp = models.CharField('Kostentyp', max_length=10, choices=KOSTENTYP_CHOICES)
+    gas_volume = models.DecimalField('Gasvolumen (Liter)', max_digits=10, decimal_places=2, null=True, blank=True)
+    betrag = models.DecimalField('Betrag (€)', max_digits=10, decimal_places=2)
+    beschreibung = models.TextField('Beschreibung', blank=True)
+    
+    @property
+    def price_per_liter(self):
+        if self.kostentyp == 'helium' and self.gas_volume:
+            return self.betrag / self.gas_volume
+        return None
+    
+    def __str__(self):
+        return f"{self.buchungsdatum} - {self.get_kostentyp_display()} - {self.betrag}€"  # Fixed the missing quote
 
 class Client(models.Model):
     name = models.CharField(max_length=100)