django注释-在模板中计数嵌套项的问题

Question

我有一个商业挑战的复选框和标签的列表。我想为每一个商业挑战申请类别，但我正在努力计数每一个类别的商业挑战数量。

这就是我所拥有的：

models.py

class BusinessChallangeCategory(models.Model):
    title = models.CharField(max_length=300)
        
class BusinessChallange(models.Model):
    title = models.CharField(max_length=300)
    category = models.ForeignKey(BusinessChallangeCategory, on_delete=models.CASCADE, related_name='category_business_challange')

class Product(models.Model):
    title = models.CharField(max_length=300)
    business_challange = models.ManyToManyField(BusinessChallange, related_name='business_challange_product')

views.py

class ManualSearch(ListView):
    template_name = 'test.html'
    model = Product
    queryset = Product.objects.filter(status=1)
    
    def get_context_data(self, **kwargs):
        context = super(ManualSearch, self).get_context_data(**kwargs)
        business_challange = BusinessChallangeCategory.objects.annotate(business_challange_count=Count('category_business_challange__business_challange_product'))

        context['business_challange'] = business_challange
        return context

test.html

<div class="filter-container" id="business-challange-list">
    <strong class="f-12">Business challanges</strong><br>
    {% for bc_category in business_challange %}
    <div class="fw-bold f-12">{{bc_category.title}}</div>
        {% for bc in bc_category.category_business_challange.all %}
        <div class="form-check d-flex business-challange-item">
            <input class="form-check-input" type="checkbox" value="{{bc.title}}" id="{{bc.title}}" data-filter="business_challange">
            <label class="form-check-label ps-2" for="{{bc.title}}">
                {{bc.title}}
            </label>
            <span class="ms-auto ps-2 text-muted f-12">{{bc.business_challange_count}}</span> #count is not working, it doesn't appear at all
        </div>
        {% endfor %}
    {% endfor %}
</div>

任何关于我做错了什么以及如何正确计算每一类业务挑战的建议，我们将不胜感激。

Answer 1

在模板business_challange中对一个查询集中的值进行注释，但在迭代另一个queryset bc_category.category_business_challange.all时尝试访问它，每次运行时调用DB。您不需要注释，尽管可以直接调用{{bc.business_challange_product.count}}。不过，每个查询都会发出另一个查询。

从性能的角度来看，我建议直接对BusinessChallange的第二个查询集进行注释，而不是在python中按类别对BusinessChallangeCategory和组进行注释，这样您就可以在一个查询和一个for循环迭代中得到所需的内容。