如何在django中将模型对象添加到购物车中

from django.db import models
from django.contrib.auth.models import User

class Cart(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField(default=1)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return f"{self.user.username} - {self.product.name}"

from django.shortcuts import redirect, get_object_or_404
from .models import Cart, Product

def add_to_cart(request, product_id):
    product = get_object_or_404(Product, id=product_id)
    cart, created = Cart.objects.get_or_create(user=request.user, product=product)
    
    if not created:
        cart.quantity += 1
        cart.save()
    
    return redirect('cart')  # 跳转到购物车页面

from django.shortcuts import render
from .models import Cart

def cart(request):
    cart_items = Cart.objects.filter(user=request.user)
    total_quantity = Cart.objects.filter(user=request.user).aggregate(total_quantity=models.Sum('quantity'))
    total_items = Cart.objects.filter(user=request.user).count()
    
    context = {
        'cart_items': cart_items,
        'total_quantity': total_quantity['total_quantity'],
        'total_items': total_items
    }
    
    return render(request, 'cart.html', context)

{% for item in cart_items %}
    <p>{{ item.product.name }} - {{ item.quantity }}</p>
{% empty %}
    <p>No items in the cart.</p>
{% endfor %}

<p>Total Quantity: {{ total_quantity }}</p>
<p>Total Items: {{ total_items }}</p>