How to merge guest cart item and user cart Django?

Question

I am trying to merge guest cart (session cart) items and existing user cart. if cart items repeating increase quantity else, create a new cart item.

In my case user already have a cart. in it three products [, , ]

then the user logged out and add some products [, ] , then when he login again, the repeating product should add quantity, not as a repeating product. and the new product should show as new product in the cart.

but my code results always repeating product in the cart?

def user_login(request):
    if request.user.is_authenticated :
        return redirect('home')
    else:

        if request.method == 'POST':
            email = request.POST['email']
            password = request.POST['password']
            
            user= authenticate(email =email, password = password)
            if user is not None:
                try:
                  cart = Cart.objects.get(cart_id = _cart_id(request))
                  is_cart_item_exists = CartItem.objects.filter(cart=cart).exists()

                  if is_cart_item_exists:
                    cart_items = CartItem.objects.filter(cart=cart)
                    new_cart_items = []
                    for cart_item in cart_items:
                      item = cart_item
                      new_cart_items.append(item)

                    print(new_cart_items)

                    cart_items = CartItem.objects.filter(user=user)
                    existing_cart_items = []
                    id =[]
                    for cart_item in cart_items:
                      item = cart_item
                      existing_cart_items.append(item)
                      id.append(cart_item.id)

                    print(existing_cart_items)
                    print(id)
                  
                    for new_cart_item in new_cart_items:
                      print(new_cart_item)
                      if new_cart_item in existing_cart_items:  #i think this if condition always returns false, even if new_cart_item is in existing_cart_item.
                        index=existing_cart_items.index(new_cart_item)
                        item_id=id[index]
                        item=CartItem.objects.get(id=item_id)
                        item.quantity += 1
                        item.user=user
                        item.save()
                        print('added to existing items')
                      else:
                        cart_items = CartItem.objects.filter(cart=cart)
                        for cart_item in cart_items:
                            cart_item.user = user
                            cart_item.save()
                        print('added as a new item')
                        

                except:
                  pass

                login(request, user)
                return redirect('home')
            else:
                messages.error(request, "Invalid login credentials")
        return render(request, 'accounts/login.html')

Cart and CartItem model

class Cart(models.Model):
  cart_id = models.CharField(max_length=255, blank=True)
  date_created = models.DateField(auto_now_add=True)

  def __str__(self):
    return self.cart_id

class CartItem(models.Model):
  user = models.ForeignKey(CustomUser, on_delete=models.CASCADE, null=True)
  cart = models.ForeignKey(Cart, on_delete=models.CASCADE, null=True)
  product = models.ForeignKey(Products, on_delete=models.CASCADE)
  quantity = models.IntegerField()
  is_active = models.BooleanField(default=True)
  modified_time = models.DateTimeField(auto_now=True)

  def item_total(self):
    return self.product.price * self.quantity
    
  def __str__(self):
    return self.product.name

terminal

[, ]
[, , ]
[75, 73, 74]
The Alchemist
added as a new item
Sapiens: a Brief History of Human Kind
added as a new item

_cart_id function

def _cart_id(request):
  cart_id = request.session.session_key
  if not cart_id:
    car_id = request.session.create()
  return cart_id

I think if condition in above always returns false, even if new_cart_item is in existing_cart_item.

Ahmet Burak · Answer

Rather than checking all the items one by one, you can try something like this in your condition block

from django.db import Count

user_card_qs = CartItem.objects.filter(user=user)
cart_qs = CartItem.objects.filter(cart=cart)

# get the count of products in the cart
cart_products = dict(
    cart_qs.values('product')
    .annotate(product_count=Count('product'))
    .values_list('product', 'product_count')
)

is_updated = False  # not sure we need this flag

# filter only existing items. if no items loop won't iterate
for item in user_card_qs.filter(product__in=cart_products.keys()):
    item.quantity += cart_products[item.product]
    is_updated = True
    
if is_updated:
    # update all the items that exists in the users cart
    CardItem.objects.bulk_update(user_card_qs, update_fields=['quantity'])

How to merge guest cart item and user cart Django?

1 Answers