Calculate the sum and multiply with the quantity to get the total in django

Question

I have the code which calculates the sum just fine, now my question is it possible to multiple each price by quantity and then get the total sum after that in a cart on my website. I have tried with all of my logic but i have failed. The idea is to get the price of an item added to cart and multiply it by quantity and then get the total. Here is my cart mode. models.py: #cart model

 class Cart(models.Model):
  item = models.ForeignKey(Item, on_delete=models.CASCADE)
  number_of_items = models.IntegerField(default=0)
  user = models.ForeignKey(User, on_delete=models.CASCADE)
  added_datetime = models.DateTimeField(auto_now_add=True)


  def __str__(self):
      return self.item.name
 #Item model 


class Item(models.Model):
CONDITION = (
        ('new', 'new'),
        ('used', 'used'),
  ('not applicable', 'not applicable'),
        
        ) 
name = models.CharField(max_length=250)
owner = models.CharField(max_length=250, default='Ludocs-emark')
category = models.ForeignKey(ItemCategories, on_delete=models.CASCADE)
sub_category = models.ForeignKey(SubCategory, on_delete=models.CASCADE)
tag = models.ForeignKey(Tag, on_delete=models.CASCADE)
Condition = models.CharField(max_length=250, null=True, choices=CONDITION)
price= models.IntegerField(default=0)
number_of_items = models.IntegerField(blank=True)
specification_one = models.CharField(max_length=250, blank=True)
specification_two = models.CharField(max_length=250, blank=True)
specification_three = models.CharField(max_length=250, blank=True)
specification_four = models.CharField(max_length=250, blank=True)
specification_five = models.CharField(max_length=250, blank=True)
specification_six = models.CharField(max_length=250, blank=True)
available_colors = models.CharField(max_length=250, blank=True)
description = RichTextField()


thumbnail = models.ImageField(default='default.png', upload_to='images/')
image_one = models.ImageField(upload_to='images/')
image_two = models.ImageField(upload_to='images/')
image_three = models.ImageField(upload_to='images/')
image_four = models.ImageField(upload_to='images/')
added_date = models.DateTimeField(auto_now_add=True)


def __str__(self):
  return self.name

views.py file that i used to calculate the sum: #This is the file where that i want to use to get the items added in cart and then multiply each by it's quantity and then get the total of the calculations when multiplied.

  cart_sum = Cart.objects.filter(user=request.user).aggregate(Sum('item__price')).get('item__price__sum')

Answer 1

Yes, You can do that. Try this

cart_sum = Cart.objects.filter(user=request.user).aggregate(Sum('item__price', field='item__price  * number_of_items')).get('item__price__sum')

Assuming number_of_items as the quantity for the item from the Cart model. Also you can return a total value so that if this gives any error for two different fields then you can do this

cart_sum = Cart.objects.filter(user=request.user).aggregate(total_price=Sum('item__price', field='item__price * number_of_items')).get('total_price')