Haystack says “Model could not be found for SearchResult”

Question

After updating my Django from 1.7 to 1.9, search engine, which is based on Haystack and Solr, stopped working. This is what I get:

./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')>'.

I have to say my database is not empy and my configuration is as follow:

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

And this is my search_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

Answer 1

I was able to fix the issue by including a missing commit to the 2.4.1 release. The commit that fixed this issue was https://github.com/django-haystack/django-haystack/commit/f1ed18313777005dd77ed724ecbfb27c0b03cad8

so you can do

pip install git+ssh://git@github.com/django-haystack/django-haystack.git@f1ed18313777005dd77ed724ecbfb27c0b03cad8

to install until that specific commit.