4

I'm displaying 7 random objects on a home page. For that I use solution based on this answer:

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')

If I pass prefetch_related=Prefetch('productphoto_set', queryset=ProductPhoto.objects.order_by('pk')) to random_impl method, it prefetches 1 photo at a time for each product. Which is not surprising. Can I prefetch related objects manually after products has already been fetched?

x-yuri
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1 Answers1

6

To my surprise, there's a legal way. Documented, that is. You just need to add:

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