How to get the difference of 2 different django models fields?

Question

I have here 2 django database table

class ProductName(models.Model):
     name = models.CharField(max_length=100)

class Inventory(models.Model):
     product = models.ForeignKey(ProductName, on_delete = models.CASCADE )
     qty = models.PositiveIntegerField()

class Sold(models.Model):
     product = models.ForeignKey(ProductName, on_delete = models.CASCADE )
     qty = models.PositiveIntegerField()

I would like to have an inventory table page wherein I can see the total qty left in Inventory (for example: Inventory.qty - Sold.qty) .

how to do this in Django ?

Answer 1

In your views file

from .model import Inventory, Sold

qty_left = Inventory.objects.count() - Sold.objects.count()