Question

I am creating a basic shopping cart application, I can get in my cart all of the items to populate with the quantity and cost, but I am trying to find a way thats I can create a total cost, and adding sales tax on top of that. Clearly the total line is the issue, but I am not sure what I could do to populate price and quantity for all products and multiply them together.

{% for addtocart in userCart %}
  <li>Quantity:{{addtocart.quantity}} <a href="/products/{{addtocart.product.id}}">{{addtocart.product.prodName}}</a> ${{addtocart.product.prodPrice}}(<a
href=/delItem/{{addtocart.id}}>Remove</a>)<br>
{% endfor %}
</ul>
{% else %}
<p> No products available </p>
{% endif %}
***<p>Total: {{addtocart.quantity}}"x"{{addtocart.product.prodPrice}}***

views.py

def addtocart(request, prod_id):
        if (request.method == 'POST'):
                form = CartForm(request.POST)
                if form.is_valid():
                        newComment = form.save()
                        newComment.session = request.session.session_key[:20]
                        newComment.save()
                        return HttpResponseRedirect('/products/' + str(newComment.product.id))
        else:
                form = CartForm( {'name':'Your Name', 'session':'message', 'product':prod_id} )

        return render_to_response('Products/comment.html', {'form': form, 'prod_id': prod_id})

def userHistory(request):
        userCart = Cart.objects.filter(session = request.session.session_key[:20])
        return render_to_response('Products/history.html', {'userCart':userCart})

models.py

from django.db import models
from django.forms import ModelForm

# Create your models here.
class prod(models.Model):
        prodName = models.CharField(max_length=100)
        prodDesc = models.TextField()
        prodPrice = models.FloatField()
        prodImage = models.ImageField(upload_to="userimages/")
        def __unicode__(self):
                return self.prodName

class Cart(models.Model):
        session = models.CharField(max_length=100)
        product = models.ForeignKey('prod')
        quantity = models.IntegerField()

        def __unicode__(self):
                return self.name

class CartForm(ModelForm):
        class Meta:
                model = Cart
                exclude = ('session')

Answer 1

There are two ways you can do this:

1. compute the total in your view, and pass it in as a separate variable
2. define a custom template tag that does multiplication (Django doesn’t have one by default)

(1) in more detail:

In your view:

def userHistory(request):
    userCart = Cart.objects.filter(session = request.session.session_key[:20])
    totalCost = 0
    for item in userCart:
        totalCost += item.quantity * item.product.prodPrice
    return render_to_response('Products/history.html', {'userCart':userCart,
        'totalCost': totalCost})

Then in your template:
<p>{{totalCost}}</p>

(2) in more detail:

First make a new file my_app/templatetags/my_tags.py (also put an __init__.py file in this directory, so that Python knows it’s a package)

from django import template
register = template.Library()

@register.filter 
def multiply(arg1, arg2): 
    return float(arg1) * float(arg2)

Then in your template add {% load my_tags %} at the top, and you’ll be able to use {{addtocart.quantity|multiply:addtocart.product.prodPrice}}