How do I collect multiple Django models together into a single list?

Question

I have a fairly straightforward blog in Django, with separate models for Article and Link. I want to have a loop in my template that lists them both in date order, which means something like this:

def listview(request):
    return render_to_response('index.dtmpl', {
        'articles' : ArticlesAndLinks.objects.order_by('post_date')[:10]
    }, context_instance = RequestContext(request)

I'm not sure how to do this. Do I have to grab Articles.objects.order_by('post_date') and Links.objects.order_by('post_date') separately, merge them, and reorder? Or is there a nicer Django-ish/Pythonic way to accomplish this?

If it helps, Posts and Links are both subclasses of an abstract class, Post, but as it's an abstract class it appears I can't run collections on it.

Answer 1

事实证明，解决方案是将抽象类变成一个真正的类，然后我可以收集它。

Answer 2

Well, the obvious answer would have been to make Post a concrete class. Else you'll probably have to squeeze the ORM and resort to handcoded SQL or manually merge/order your two querysets. Given the small size of the dataset, I'd go for this last solution.

Answer 3

Refactoring could be the better solution, but here is another one that could do the job:

Create a custom Manager:

class PostManager(models.Manager):
    def mixed(self, first):
        all_dates = []
        articles_dates = Articles.objects.extra(select={'type':'"article"'}).values('id', 'post_date', 'type').order_by('-post_date')[:first]
        links_dates = Links.objects.extra(select={'type':'"link"'}).values('id', 'post_date', 'type').order_by('-post_date')[:first]
        all_dates.extend(articles_dates)
        all_dates.extend(links_dates)
        # Sort the mixed list by post_date, reversed
        all_dates.sort(key=lambda item: item['post_date'], reverse=True)
        # Cut first 'first' items in mixed list
        all_dates = all_dates[:first]
        mixed_objects = []
        mixed_objects.extend(Articles.objects.filter(id__in=[item['id'] for item in all_dates if item['type'] = 'article']))
        mixed_objects.extend(Links.objects.filter(id__in=[item['id'] for item in all_dates if item['type'] = 'link']))
        # Sort again the result list
        mixed_objects.sort(key=lambda post: post.post_date, reverse=True)
        return mixed_objects

And use it in your abstract model:

class Post(models.Model):

    class Meta:
        abstract = True

    objects = PostManager()

Then the call for your mixed objects will be:

Article.objects.mixed(10)