combined_recent() function for union across querysets returning most recent objects. See https://simonwillison.net/2018/Mar/25/combined-recent-additions/

combined_recent.py

from django.db.models import Value, CharField


def combined_recent(limit, **kwargs):
    datetime_field = kwargs.pop('datetime_field', 'created')
    querysets = []
    for key, queryset in kwargs.items():
        querysets.append(
            queryset.annotate(
                recent_changes_type=Value(
                    key, output_field=CharField()
                )
            ).values('pk', 'recent_changes_type', datetime_field)
        )
    union_qs = querysets[0].union(*querysets[1:])
    records = []
    for row in union_qs.order_by('-{}'.format(datetime_field))[:limit]:
        records.append({
            'type': row['recent_changes_type'],
            'when': row[datetime_field],
            'pk': row['pk']
        })
    # Now we bulk-load each object type in turn
    to_load = {}
    for record in records:
        to_load.setdefault(record['type'], []).append(record['pk'])
    fetched = {}
    for key, pks in to_load.items():
        for item in kwargs[key].filter(pk__in=pks):
            fetched[(key, item.pk)] = item
    # Annotate 'records' with loaded objects
    for record in records:
        record['object'] = fetched[(record['type'], record['pk'])]
    return records

# recent = combined_recent(
#     20,
#     entry=Entry.objects.all(),
#     photo=Photo.objects.all(),
# )