cart session in Django

Question

I use the session to create a shopping cart. I have a product model and a model for Variant, which I color and size my products in the Variant model. So that I can have products with different colors and sizes as well as different prices. The shopping cart I created with Session has a problem. The problem I have is that if the product has 3 different colors and each color has a different price, I have trouble displaying the price in the cart and I do not know how to act. How should I display the prices of my Variant model in the template?

my Product model:
class Product(models.Model):
    name = models.CharField(max_length=200)
    price = models.IntegerField(default=0)

my Variant model:
class Variants(models.Model):
    name = models.CharField(max_length=100)
    product = models.ForeignKey(Product, on_delete=models.CASCADE, related_name='product_var',)
    size = models.ForeignKey(Size, on_delete=models.CASCADE)
    color = models.ForeignKey(Color, on_delete=models.CASCADE)
    price = models.IntegerField(default=0)

my session cart :

CART_SESSION_ID = 'cart'

class Cart:
    def __init__(self, request):
        self.session = request.session
        cart = self.session.get(CART_SESSION_ID)
        if not cart:
            cart = self.session[CART_SESSION_ID] = {}
        self.cart = cart

    def __iter__(self):
        product_ids = self.cart.keys()
        products = Product.objects.filter(id__in=product_ids)
        cart = self.cart.copy()
        for product in products:
            cart[str(product.id)]['product'] = product
            
    def add(self, product, quantity):
        product_id = str(product.id)
        if product_id not in self.cart:
            self.cart[product_id] = {'quantity': 0, 'price': str(product.total_price)}
        self.cart[product_id]['quantity'] += quantity
        self.save()

    def save(self):
        self.session.modified = True

my view:
# show cart
def cart_details(request):
    cart = Cart(request)
    return render(request, 'cart/cart_details.html', {'cart': cart, })

# add to cart
def cart_add(request, product_id):
    cart = Cart(request)
    product = get_object_or_404(Product, id=product_id)
    form = CartAddForm(request.POST)
    if form.is_valid():
        cd = form.cleaned_data
        cart.add(product=product, quantity=cd['quantity'])
    return redirect('cart:details')

my template for show product in cart:
{% for c in cart %}
    <tr>     
        <td>{{ c.product.name }}</td>
        <td>{{ c.product.price }}</td> # my problem!!!
    </tr>
{% endfor %}

Answer 1

From the problem statement I see that problem will go away if you store variants in shopping cart instead of products.

The code will change to something like this:

class Cart:
    def __init__(self, request):
        self.session = request.session
        cart = self.session.get(CART_SESSION_ID)
        if not cart:
            cart = self.session[CART_SESSION_ID] = {}
        self.cart = cart

    def __iter__(self):
        variant_ids = self.cart.keys()
        products = Variants.objects.filter(id__in=variant_ids)
        cart = self.cart.copy()
        for product in products:
            cart[str(variant.id)]['variant'] = variant
            
    def add(self, variant, quantity):
        variant_id = str(variant.id)
        if variant_id not in self.cart:
            self.cart[variant_id] = {'quantity': 0, 'price': str(variant.price)}
        self.cart[variant_id]['quantity'] += quantity
        self.save()

    def save(self):
        self.session.modified = True

# add to cart
def cart_add(request, variant_id):
    cart = Cart(request)
    variant = get_object_or_404(Variant, id=variant_id)
    form = CartAddForm(request.POST)
    if form.is_valid():
        cd = form.cleaned_data
        cart.add(variant=variant, quantity=cd['quantity'])
    return redirect('cart:details')

template
{% for c in cart %}
    <tr>     
        <td>{{ c.variant.name }}</td>
        <td>{{ c.variant.price }}</td>
        <td> color, etc.</td>
    </tr>
{% endfor %}

You don't need to store the product in cart anymore since variant has relation with product table.