I'm trying to add extra models to an ordered list of items and have everything in the list ordered by a date field on each model.
I thought I'd cracked it by chaining each queryset and sorting them with a key;
def get_ordering(obj):
"""
Helper to get the 'order_by' field for the paginated latest news list.
:param obj: Object used in the paginated latest news
:type obj: django.db.model
:return: ordering field
:rtype: str
"""
if isinstance(obj, LatestNews):
return '-publish_date'
else:
return '-date_created'
def build_paginated_latest_news(request, instance=None, placeholder=None):
paginated_page_no = get_page_no(request)
paginated_page_items = get_page_items(request)
latest_news = LatestNews.cached.published_items(
request, instance, placeholder
)
query = published_items(request)
videos = VideoGalleryPlugin.objects.filter(query)
audio = Audio.objects.filter(query)
obj_list = sorted(
chain(latest_news, videos, audio),
key=lambda instance: get_ordering(instance)
)
paginator = Paginator(obj_list, paginated_page_items)
But ultimately the list that's rendered is displayed as videos, audio, latest_news which isn't even the order I chain them all together.
Is it correct to apply a key like this with sorted() to combine querysets?
In the get_ordering() you should return the value which will be used by the sorting function:
def get_ordering(obj):
if isinstance(obj, LatestNews):
return obj.publish_date
else:
return obj.date_created
And then in your view:
obj_list = sorted(
chain(latest_news, videos, audio),
key=get_ordering, # intermediate lambda is not needed here
reverse=True
)
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