掌握Django类视图：正确向模板传递多值数据

from django.views.generic import ListView
from django.db.models import Sum
from .models import Product # 假设你有一个Product模型

class ShopListing(ListView):
    template_name = "webshop/shop_listing.html"
    context_object_name = 'shop_listing' # 默认会将查询集命名为shop_listing

    def get_queryset(self):
        # 获取所有产品
        products = Product.objects.all()
        # 计算总库存
        total_stock = products.aggregate(sum=Sum('stock'))['sum']
        # 尝试返回产品和总库存
        return products, total_stock

<!-- webshop/shop_listing.html -->
<p><strong>{{ total_stock }}</strong> items are currently available</p>
{% for product in shop_listing %}
    <!-- 显示产品信息 -->
{% endfor %}

from django.views.generic import ListView
from django.db.models import Sum
from .models import Product

class ShopListing(ListView):
    template_name = "webshop/shop_listing.html"
    context_object_name = 'shop_listing'
    # 对于简单的查询集，可以直接定义queryset属性
    queryset = Product.objects.all() 

    def get_context_data(self, **kwargs):
        # 首先调用父类的方法，获取默认的上下文数据
        context = super().get_context_data(**kwargs)

        # 添加自定义数据到上下文字典中
        # 注意：这里可以直接对Product模型进行聚合查询，
        # 因为我们需要的总库存与get_queryset返回的产品列表是独立计算的。
        context['total_stock'] = Product.objects.aggregate(sum=Sum('stock'))['sum']

        # 返回更新后的上下文
        return context

<!-- webshop/shop_listing.html -->
<h1>产品列表</h1>
<p>当前共有 <strong>{{ total_stock }}</strong> 件商品有库存。</p>

<h2>所有产品：</h2>
<ul>
    {% for product in shop_listing %}
        <li>{{ product.name }} - 库存: {{ product.stock }}</li>
    {% empty %}
        <li>暂无产品。</li>
    {% endfor %}
</ul>

class FilteredShopListing(ListView):
    template_name = "webshop/shop_listing.html"
    context_object_name = 'shop_listing'

    def get_queryset(self):
        category_id = self.kwargs.get('category_id') # 从URL中获取分类ID
        if category_id:
            return Product.objects.filter(category_id=category_id)
        return Product.objects.all()

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        # 即使get_queryset动态生成了产品列表，我们仍然可以在这里计算总库存
        # 如果total_stock也需要根据category_id过滤，则应在get_context_data中重新执行过滤后的聚合
        context['total_stock'] = Product.objects.aggregate(sum=Sum('stock'))['sum']
        return context