Django Model Signals and Database Consistency

from django.db.models.signals import post_save
from django.dispatch import receiver

class Product(models.Model):
    name = models.CharField(max_length=100)
    stock = models.IntegerField(default=0)

class Order(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.IntegerField()

@receiver(post_save, sender=Order)
def update_stock(sender, instance, created, **kwargs):
    if created:
        product = instance.product
        product.stock -= instance.quantity
        product.save()

# Hari creates an order:
order = Order.objects.create(product=product, quantity=5)