Is there a way to change the amount in two fields of different models with one form?

Question

from django.db import models



class Product(models.Model):
    name = models.CharField(max_length = 50)
    quantity = models.FloatField(default=0)


def __str__(self):
    return self.name



class Customer(models.Model):
    name = models.CharField(max_length=100)
    primary_contact = models.CharField(max_length=10)
    secondary_contact = models.CharField(max_length=10)
    address = models.TextField(blank=True)


def __str__(self):
    return self.name

class Issue(models.Model):
    date = models.DateTimeField(auto_now_add = True)
    customer = models.ForeignKey(Customer, on_delete = models.CASCADE)
    product = models.ForeignKey(Product, on_delete=models.CASCADE, )
    quantity = models.PositiveIntegerField()
    kt = models.IntegerField()
    rate = models.FloatField()
    vat = models.IntegerField(default=15)

    @property
    def kt_21(self):
        return self.kt / 21 * self.quantity
    
    @property
    def vat_amt(self):
        return self.quantity * self.rate * self.vat/100

    @property
    def total_amt(self):
        return self.quantity * self.rate + self.vat_amt

    def __str__(self):
        return  str(self.customer) + " - "+ str(self.total_amt)+' SAR'

I have these models now I what I want is that when I issue a product and enter some quantity in the Issue model the same amount of quantity should be deducted from the Product model's quantity field.

Answer 1

you can simply make an update query after saving your IssueForm. Like this:

def submit_issue(request):
    if request.method == "POST":
       form = IssueForm(request.POST)
       if form.is_valid():
           form_product_qty = form.cleaned_data["quantity"]
           product_id = form.cleaned_data["product_id "]
           user = form.save()
           product = Product.objects.get(id=product_id)
           product.quantity = product.quantity - form_product_qty
           product.save()