i have the following model
class FeeModel(models.Model):
user=models.ForeignKey(User,on_delete=models.CASCADE,null=True)
total_fee=models.IntegerField(default=100000)
paid_fee=models.IntegerField()
remaining_fee=models.IntegerField(default=0)
i need the remaining_fee to be filled by the result of (total_fee - paid_fee). How would i do that?
You can do this in numerous ways and places. A pre_save signal is one approach.
(In models.py, below your FeeModel class)
from django.db.models.signals import pre_save
from django.dispatch import receiver
@receiver(pre_save, sender=FeeModel)
def set_remaining_fee(sender, instance, *args, **kwargs):
instance.remaining_fee = (instance.total_fee - instance.paid_fee)
How this works: A user enters the values for total_fee and paid_fee into a form. Upon submit and just before save(), the signal calculates the difference and applies it to the remaining_fee field. Note that this will run every time the model instance is saved.
