如何在w / django中获取类别内的项目数？

Question

在我的网站页面上，我试图显示html组件上每个类别内的帖子数量。这是我想在下面做的一个例子。

我已经在html组件上添加了类别名称。类别名称旁边的值只是用作占位符的随机数。我一直在努力获取每个类别中职位数量的价值。我真的不知道我应该使用什么查询集。

这是我的代码。

blog.py

class BlogPage(Page):
    def get_context(self, request, *args, **kwargs):
        context = super().get_context(request, *args, **kwargs)
        category_slug = request.GET.get('category', None)
        blogposts = PostPage.objects.live().public().order_by('-first_published_at')
        if category_slug == None:
            context['blogposts'] = blogposts
        else:
            context['blogposts'] = blogposts.filter(categories__slug__contains=category_slug)
            context['category_slug'] = category_slug
        context['categories'] = BlogCategory.objects.all() # category object
        return context


class PostPage(Page):
    date = models.DateField(verbose_name="Post date")
    categories = ParentalManyToManyField("blog.BlogCategory", blank=True)
    body = RichTextField(blank=False)
    main_image = models.ForeignKey(
        'wagtailimages.Image', 
        null=True,
        blank=False,
        on_delete=models.SET_NULL, 
        related_name='+')

    content_panels = Page.content_panels + [
        FieldPanel('date'),
        FieldPanel('categories', widget=forms.CheckboxSelectMultiple),
        ImageChooserPanel('main_image'),
        FieldPanel('body', classname="full"),
    ]

@register_snippet
class BlogCategory(models.Model):
    name = models.CharField(max_length=120)
    slug = models.SlugField(
        verbose_name="slug",
        allow_unicode=True,
        max_length=255,
        help_text='A slug that identify post by category.'
    )

    panels = [
        FieldPanel('name'),
        FieldPanel('slug'),
    ]

    def __str__(self):
        return self.name

blog_page.html

<ul class="cat-list">
 {% for cat in categories %}
   <li>
     <a href="?category={{cat.slug}}" class="d-flex">
       <p>{{cat.name}}</p>
       <p>{{cat.count}}</p> <!-- My attempt in trying to get the number -->
     </a>
   </li>
 {% endfor %}
</ul>

Answer 1

您可以使用Django的annotate方法将计算值添加到查询集：

https://docs.djangoproject.com/en/3.0/topics/db/aggregation/

在这种情况下，您的categories查询将变为：

from django.db.models import Count

class BlogPage(Page):
    def get_context(self, request, *args, **kwargs):
        # ...
        context['categories'] = BlogCategory.objects.annotate(num_posts=Count('postpage'))

这将允许您引用模板中的{{cat.num_posts}}。