Add quantity for every the same Client and Product in Django

I have 3 models, CustomerPurchaseOrderDetail, Customer and Product model, if Customer1 buy a product for example, Meat. it will save in CustomerPurchaseOrderDetail and if that Customer1 add another Meat Product, instead of adding another record to the database it will simply just add quantity.

this is my views.py

def batchaddtocart(request):
    userID = request.POST.get("userID")
    client = Customer(id=userID)
    vegetables_id = request.POST.get("id")

    v = Product(id=vegetables_id)
    price = request.POST.get("price")
    discount = request.POST.get("discount_price")

    insert, create = CustomerPurchaseOrderDetail.objects.get_or_create(
        profile=client,
        products=v,
        unitprice=price,
        quantity=1,
        discounted_amount=discount,
        discounted_unitprice=discount,
    )

    order_qs = CustomerPurchaseOrderDetail.objects.filter\
        (
            profile=client,
            products=v,
            unitprice=price,
            quantity=1,
            discounted_amount=discount,
            discounted_unitprice=discount
        )
    for order in order_qs:
        if order.profile == client and order.products == v:
            insert.quantity += 1
            print(insert.quantity)
            insert.save()
    insert.save()

this is my models.py

class CustomerPurchaseOrderDetail(models.Model):
    profile = models.ForeignKey(Customer, 
                                on_delete=models.SET_NULL, null=True, blank=True,
                                verbose_name="Client Account")
    products = models.ForeignKey(Product, 
                                                on_delete=models.SET_NULL, null=True, blank=True,
                                                verbose_name="Product")
    quantity = models.IntegerField(max_length=500, null=True, blank=True, default=1)

class Product(models.Model):
      product = models.CharField(max_length=500)

class Customer(models.Model):
    user = models.OneToOneField(User, related_name="profile", on_delete=models.CASCADE)
    firstname = models.CharField(max_length=500, blank=True)
    lastname = models.CharField(max_length=500, blank=True)
    contactNumber = models.CharField(max_length=500, blank=True)
    email = models.CharField(max_length=500, blank=True)

I did not encounter an error but the functionality I wanted did not work. it does not add additional quantity even if the same product is added to the list purchased by Customer1.

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