Sort django haystack results by datetime (whoosh backend)

Question

I have a SearchIndex whose results I want to be sorted based on a DatetimeField. However when I try to manage.py rebuild_index, I get a ValueError complaining about the datetime being a... datetime.

In case it matters, I use timezones and pytz, but for the sorting I want, timezones do not really matter, I just want the newest first kind of thing.

The Index

I have removed some irrelevant fields.

class ArticleIndex(indexes.SearchIndex, indexes.Indexable):
    text = indexes.CharField(document=True, use_template=True)
    publish_date = indexes.DateTimeField(model_attr='publish_date')

The view/url pair

posts_sqs = SearchQuerySet().order_by('-publish_date')

urlpatterns += patterns(
    'haystack.views',

    url(r'^search/$', search_view_factory(
        view_class=PostsSearchView,
        template='pages/search.html',
        searchqueryset=posts_sqs,
        form_class=ThreeCharMinSearchForm),  # a custom form
    name='pages.search'),

)

The rebuild_index Exception

 ValueError: datetime.datetime(2015, 1, 23, 16, 31, 28, tzinfo=<UTC>) is not unicode or sequence

I have tried to implement prepare_publish_date methods that return strftime representations ('%Y %m %d %H %M' and '%d %m %Y %H %M') with both naive and aware datetimes, timetuples, "epoch times" with a CharField instead of a DateTimeField and I can't remember what else and all failed, except for the "epoch time" version, which was terribly slow though.

As a last note, I use Python 2.7.8, Django 1.6.10 and before I tried to do this sorting, the index was working nicely (even better that what was expected), so I am pretty sure the rest of the implementation is correct.

I understand that it is Whoosh that's expecting unicode, but I don't know what to do exactly. Any thoughts?

Answer 1

Thanks for the feedback everyone, because when noone answers your question on SO, the feedback basically is "Dude, what you 're saying doesn't make sense, question your assumptions and check everything.".

So, in my case, there was a customized WhooshSearchBackend which was stripped down and did not account for DateTimeFields. For anyone stumbling upon this, Whoosh and Haystack can handle datetimes just fine. If they don't, check your setup.