Manually combine multiple Django QuerySets, and serialize result using DRF

Question

I have been researching this for a couple days. Unfortunately, all of the proposed solutions I have found so far don't exactly work for me.

I am looking to manually combine two Django QuerySets into a single Django model, which I then want to serialize using a Django Rest Framework serializer. I then use the serializer for outputting JSON.

I have found various solutions on SO suggesting the use of itertools and chain, but it is unclear then how to serialize the result of chain.

Note that my goal here is for web application performance purposes. Each QuerySet works fine independently, but it requires two separate Ajax calls to retrieve the results. I would prefer to make only one Ajax call, manually combine the results on the server-side, then return the combined JSON.

This SO answer is close, but I can't figure out how to serialize the result of a chain, using DRF serializers.

Answer 1

After a couple more days of Googling for answers to this problem, I finally stumbled on this page which explains how to do pretty much what I wanted to do. I have posted my own answer here in case someone else has the same problem.

The technique seems simple enough now that I understand it, but I had a hard time finding anything online describing this technique. Basically, you chain together multiple querysets, then convert the chain to a Python list. Then iterate the list, manually calling the correct serializer, and appending to a dictionary. Then you can dump the dictionary to JSON.

I have posted the relevant code in case that link goes dead:

    def get_queryset(self):
        queryset_a = Post.objects.all()
        queryset_b = FriendRequest.objects.filter(is_unanswered=True)

        # Create an iterator for the querysets and turn it into a list.
        results_list = list(chain(queryset_a, queryset_b))

        # Optionally filter based on date, score, etc.
        sorted_list = sorted(results_list, key=lambda instance: -instance.date_created)

        # Build the list with items based on the FeedItemSerializer fields
        results = list()
        for entry in sorted_list:
            item_type = entry.__class__.__name__.lower()
            if isinstance(entry, Post):
                serializer = PostSerializer(entry)
            if isinstance(entry, FriendRequest):
                serializer = FriendRequestSerializer(entry)

            results.append({'item_type': item_type, 'data': serializer.data})

        return results