Cart Not working properly about ecommerce HOT 2 OPEN

class CartManager(models.Manager):
    def new_or_get(self, request):
        cart_id = request.session.get("cart_id", None)
        qs = self.get_queryset().filter(id=cart_id)
        if qs.count() == 1:
            new_obj = False
            cart_obj = qs.first()
            if request.user.is_authenticated() and cart_obj.user is None:
                user_cart = self.model.objects.filter(user=request.user).first()
                if user_cart is not None:
                    cart_obj.products.add(*user_cart.products.all())
                    cart_obj.user = request.user
                    cart_obj.save()
                    user_cart.delete()
                else:
                    cart_obj.user = request.user
                    cart_obj.save()
        else:
            cart_obj = Cart.objects.new(user=request.user)
            new_obj = True
            request.session['cart_id'] = cart_obj.id
        return cart_obj, new_obj
 
    def new(self, user=None):
        user_obj = None
        if user is not None:
            if user.is_authenticated():
                cart_obj = self.model.objects.filter(user=user).first()
                if cart_obj is not None:
                    return cart_obj
                user_obj = user
        return self.model.objects.create(user=user_obj)