我想在模板中使用计数或长度功能，但我不知道如何去做。我想单独计算所有类别的项目
models.py

class Product(PolymorphicModel):
    title = models.CharField(max_length=100, blank=True)
    image = models.ImageField(upload_to='product', default=None)
    quantity = models.IntegerField(null=False)
    is_available = models.BooleanField(default=True, null=False)
    price = models.IntegerField(null=False, blank=False, default=15)
    popularity = models.IntegerField(default=0)

    def __str__(self):
        return str(self.title)

    def get_absolute_url(self):
        return reverse("ProductDetail", args=[str(self.pk)])

    @property
    def model_name(self):
        return self._meta.model_name

class CD(Product):
    GENRE_CHOICES = (
        ('Rock', 'Rock'),
        ('Pop', 'Pop'),
        ('Reggae', 'Reggae'),
        ('Disco', 'Disco'),
        ('Rap', 'Rap'),
        ('Electronic music', 'Electronic music'),

   )
    band = models.CharField(max_length=100, null=False, blank=False)
    tracklist = models.TextField(max_length=500, null=False, blank=False)
    genre = models.CharField(max_length=100, choices=GENRE_CHOICES, null=False, blank=False)

views.py 所有元素的简单列表

class ProductListView(View):
    def get(self, request):
        products = CD.objects.all()
        return render(request, 'products/statistics.html', {'products': products})