title: Haystack says “Model could not be found for SearchResult”
body: <p>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:</p>
  
  <pre><code>./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)
  &gt;&gt;&gt; from haystack.query import SearchQuerySet
  &gt;&gt;&gt; sqs = SearchQuerySet().all()
  &gt;&gt;&gt;sqs[0].pk
  u'1'
  &gt;&gt;&gt; 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 &amp;amp; Farhad Badpa'
  &gt;&gt;&gt; sqs[0].model_name
  u'artist'
  &gt;&gt;&gt; sqs[0].id
  u'mediainfo.artist.1'
  &gt;&gt;&gt; sqs[0].object
  Model could not be found for SearchResult '&lt;SearchResult: mediainfo.artist (pk=u'1')&gt;'.
  </code></pre>
  
  <p>I have to say my database is not empy and my configuration is as follow:</p>
  
  <pre><code>HAYSTACK_CONNECTIONS ={
      'default': {
          'ENGINE': 'haystack.backends.solr_backend.SolrEngine',
          'URL': 'http://ahangsolr:8983/solr',
      },
  }
  </code></pre>
  
  <p>And this is my <code>search_indexes.py</code>:</p>
  
  <pre><code>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
  </code></pre>