Модели Django с обратным полем

У меня есть проблема, которую я, кажется, не могу решить. У меня есть 2 модели с ForeignKey, как показано ниже :

class Transaction(models.Model):
   chp_reference = models.CharField(max_length=50, unique=True)
   rent_effective_date = models.DateField(null=True, blank=True)
   income_period = models.CharField(max_length=11, choices=income_period_choices)
   property_market_rent = models.DecimalField( help_text="Weekly", max_digits=7)

class FamilyGroup(models.Model):
   Transaction= models.ForeignKey(Transaction, on_delete=models.CASCADE, related_name="family_groups")
   last_rent = models.DecimalField(max_digits=7, decimal_places=2)       income_period = models.CharField(max_length=11, choices=income_period_choices)
   any_income_support_payment = models.BooleanField(null=True, blank=True)

   @property
   def rent_charged(self):
      rent_charged = self.transaction.property_market_rent - self.last_rent

now this function is good for only one instance of FamilyGroup, what I trying to do is to Subtract this rent_charged from self.transaction.property_market_rent in the next instance of FamilyGroup, so the next instance of FamilyGroup can have something like :

@property
def rent_charged(self):
   rent_charged = self.transaction.property_market_rent - rent_charged #( of the first instance) - self.last_rent

Любые мысли были бы очень признательны!

Вернуться на верх