如何为已获取的列表预取相关对象？

Question

我在主页上显示 7 个随机对象。为此，我使用基于 this answer:

的解决方案

class ProductManager(models.Manager):
    def random(self, n_products, filter={}, select_related=None):
        n_products_total = self.filter(**filter).count()
        if n_products_total == 0:
            return []
        r = [self.random_impl(n_products_total, filter, select_related) for i in range(n_products)]
        return [p for p in r if p is not None]

    def random_impl(self, n_products, filter, select_related=None):
        random_index = randint(0, n_products - 1)
        try:
            return self.filter(**filter) \
                .select_related(select_related)[random_index]
        except IndexError:
            return None

random_products = Product.objects.random(7, filter={'enabled': True}, select_related='category')

如果我将 prefetch_related=Prefetch('productphoto_set', queryset=ProductPhoto.objects.order_by('pk')) 传递给 random_impl 方法，它会为每个产品一次预取 1 张照片。这并不奇怪。我可以在产品已经被提取后手动预提取相关对象吗？

Answer 1

令我惊讶的是，有一个 legal way。记录在案，即。您只需要添加：

prefetch_related_objects(random_products, Prefetch('productphoto_set', queryset=ProductPhoto.objects.order_by('pk')))

如何为已获取的列表预取相关对象？

How do I prefetch related objects for a list of already fetched ones?

django

django-models

django-orm