无法在表格的初始值中显示项目数量

Question

我在网上开店。在购物车（views.show_cart）视图中，当前显示“产品”，“单价”，“数量”，“总价”，然后是允许您更新数量的表单，以及每个的“更新”按钮购物车中的产品。

我希望表单的初始值与购物车中已有的每件商品（产品）的“数量”相匹配。但是，我不能让这个工作。我尝试通过cart_items（在views.show_cart中）循环获取item.quantity，然后将其作为表单中的初始值添加，但每个项目的数量显示最后一项的数量。换句话说，购物车中有2个商品，一个数量为3，另一个数量为7.两个商品形式均显示为7。

#the form
PRODUCT_QUANTITY_CHOICES = [(i, str(i)) for i in range(1, 21)]
class ProductAddToCartForm(forms.Form):
    quantity = forms.TypedChoiceField(choices=PRODUCT_QUANTITY_CHOICES, coerce=int)
    update = forms.BooleanField(required=False,initial=False,widget=forms.HiddenInput(attrs={'class': 'form-control'}))

#cart view (cart_id.views.show_cart)
def show_cart(request):
    cart_id = _cart_id(request)
    cart_items = CartItem.objects.filter(cart_id=cart_id)
    for item in cart_items:
        q = item.quantity
        print q    #prints to shell w/correct quantities.
    add_product_form = ProductAddToCartForm(initial={'quantity': q})
    context = {'cart_items': cart_items, 'add_product_form': add_product_form}

这是涉及的另一个视图（cart_id.views.cart_add）

def cart_add(request, product_slug):
    cart_id = _cart_id(request)
    p = get_object_or_404(Product, slug=product_slug)
    cart_products = CartItem.objects.filter(cart_id=cart_id)
    product_in_cart = False
    if request.method == 'POST':        
        form = ProductAddToCartForm(request.POST)
        if form.is_valid():
            cd = form.cleaned_data
            quantity = cd['quantity']
            update = cd['update']
            for cart_item in cart_products:
                if cart_item.product.id == p.id:
                    cart_item.quantity = quantity    
                    cart_item.save()
                    product_in_cart = True
            if not product_in_cart:
                ci = CartItem()
                ci.product = p
                ci.quantity += quantity    
                ci.cart_id = cart_id
                ci.save()        
            return redirect('cart:show_cart')

模板（cart.html）

    {% extends 'base.html' %}
    {% load staticfiles %}

    {% block title %}Shopping Cart{% endblock %}
    {% block content %} {% endblock %}
    {% block extra_content %}
    <div class="container">
        <div class="col-md-12">

        h2>Cart</h2>
    <caption><b>Your Shopping Cart:</b> {{ cart_items_count }} Items In Your Cart.</caption>    
    <hr>

        {% for item in cart_items %}
        <table class="table table-striped">
             <thead>
                <tr>
                    <th>Product</th>
                    <th>Unit Price</th>
                    <th>Quantity</th>
                    <th>Total Price</th>
                </tr>
            </thead>

             <tbody>
                <tr>
                    <td><a href="{{ item.product.get_absolute_url }}">{{ item.product }}</a></td>
                    <td>${{ item.product.price }}</td> 
                    <td>{{ item.quantity }}</td>
                    <td>{{ item.total }}</td>
                    <td>
                    <div class="form-group">
                        <form action="{% url 'cart:add' item.product.slug %}" method="POST">                                
                                {% csrf_token %}
                            <div class="col-xs-3">
                                {{ add_product_form.quantity }}
                            </div>                                
                                {{ add_product_form.update }}                                                                
                            <input class='btn btn-success btn-sm' type='submit' value='Update'/>                                
                        </form>
                    </div>
                    </td>
                    </tr>
                </tbody>
            </table>
            {% empty %}
            <h3>You Have Nothing In Your Cart.</h3>
        {% endfor %}
    </div>
</div>    
{% endblock %}

模特：

class CartItem(models.Model):
    cart_id = models.CharField(max_length=50, db_index=True)
    date_added = models.DateTimeField(auto_now_add=True)
    quantity = models.IntegerField(default=1)
    product = models.ForeignKey(Product)

如果需要，这是github上的完整代码：https://github.com/chriskavanagh/ecommerce/tree/master/src。我为这篇文章中的错误间距道歉。