title: how to update a model data from the admin panel in django
body: <p>so i was creating a ecommerce site , what i wanted to do was when i added a product through admin panel , it would increase the count as well from model.
  eg:
  in the below model ,when i add an a item from admin panel i want it to find the object and add the objects stock with the new stock number i provided , if both these added items have the same names.</p>
  
  <pre><code>
  class Item(models.Model):
      name = models.CharField(max_length=100)
      price = models.FloatField()
      product = models.ForeignKey(Product, on_delete=models.CASCADE)
      desc = models.TextField()
      img = models.ImageField(upload_to='uploads/items', blank=True)
      stock = models.IntegerField()
  
  
      def __str__(self):
          return self.name
  </code></pre>