Depois de atualizar meu Django de 1.7 para 1.9, o mecanismo de pesquisa, baseado no Haystack e Solr, parou de funcionar. Isto é o que eu recebo:

./manage.py shell
Python 2.7.6 (default, Jun 22 2015, 17:58:13)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from haystack.query import SearchQuerySet
>>> sqs = SearchQuerySet().all()
>>>sqs[0].pk
u'1'
>>> sqs[0].text
u'\u06a9\u0627\u0645\u0631\u0627\u0646 \u0647\u0645\u062a\u200c\u067e\u0648\u0631 \u0648 \u0641\u0631\u0647\u0627\u062f \u0628\u0627\u062f\u067e\u0627\nKamran Hematpour & Farhad Badpa'
>>> sqs[0].model_name
u'artist'
>>> sqs[0].id
u'mediainfo.artist.1'
>>> sqs[0].object
Model could not be found for SearchResult '<SearchResult: mediainfo.artist (pk=u'1')>'.

Devo dizer que meu banco de dados não é empy e minha configuração é a seguinte:

HAYSTACK_CONNECTIONS ={
    'default': {
        'ENGINE': 'haystack.backends.solr_backend.SolrEngine',
        'URL': 'http://ahangsolr:8983/solr',
    },
}

E este é o meusearch_indexes.py:

import datetime
from haystack import indexes
from mediainfo.models import Album
from mediainfo.models import Artist
from mediainfo.models import PlayList
from mediainfo.models import Track
from mediainfo.models import Lyric

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

    def get_model(self):
        return Album

    def index_queryset(self, using=None):
        """Used when the entire index for model is updated."""
        return self.get_model().objects.filter(publish_date__lte=datetime.datetime.now())


class ArtistIndex(indexes.SearchIndex, indexes.Indexable):
    text = indexes.CharField(document=True, use_template=True)

    def get_model(self):
        return Artist


class PlaylistIndex(indexes.SearchIndex, indexes.Indexable):
    text = indexes.CharField(document=True, use_template=True)

    def get_model(self):
        return PlayList


class TrackIndex(indexes.SearchIndex, indexes.Indexable):
    text = indexes.CharField(document=True, use_template=True)

    def get_model(self):
        return Track


class LyricIndex(indexes.SearchIndex, indexes.Indexable):
    text = indexes.CharField(document=True, use_template=True)

    def get_model(self):
        return Lyric