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POHacker News algorithm for django-voting sort order
 

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  1. POHacker News algorithm for django-voting sort order
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    <p>I'm working on an application using <a href="http://code.google.com/p/django-voting/" rel="nofollow">django-voting</a> and have the sort order of the homepage items working using <a href="http://eflorenzano.com/blog/2008/05/24/managers-and-voting-and-subqueries-oh-my/" rel="nofollow">Eric Florenzano's custom VoteAwareManager technique</a>: </p> <p><strong>models.py</strong></p> <pre><code>class VoteAwareManager(models.Manager): """ Get top votes. hot = VoteAwareManager() """ def _get_score_annotation(self): model_type = ContentType.objects.get_for_model(self.model) table_name = self.model._meta.db_table return self.extra(select={ 'score': 'SELECT COALESCE(SUM(vote),0) FROM %s WHERE content_type_id=%d AND object_id=%s.id' % (Vote._meta.db_table, int(model_type.id), table_name) } ) def most_loved(self,): return self._get_score_annotation().order_by('-score') def most_hated(self): return self._get_score_annotation().order_by('score') class Post(models.Model): """Post model""" title = models.CharField(_("title"), max_length=200, blank=False) slug = models.SlugField(_("slug"), blank=True) author = models.ForeignKey(User, related_name="added_posts") kind = models.CharField(max_length=1, choices=KIND, default=1) url = models.URLField(blank=True, null=True, help_text="The link URL", default='') content_markdown = models.TextField(_("Entry"), blank=True) content_html = models.TextField(blank=True, null=True, editable=False) status = models.IntegerField(_("status"), choices=STATUS_CHOICES, default=IS_PUBLIC) allow_comments = models.BooleanField(_("Allow Comments?"), blank=False, default=1) created_at = models.DateTimeField(_("created at"), default=datetime.now) updated_at = models.DateTimeField(_("updated at")) objects = models.Manager() hot = VoteAwareManager() </code></pre> <p><strong>views.py</strong></p> <pre><code>def homepage(request): """Show top posts""" return object_list(request, queryset=Post.hot.most_loved().filter(status=IS_PUBLIC), template_name='homepage.html', template_object_name='post', extra_context= {'profile': get_profiles} ) </code></pre> <p><strong>I would now like to combine <a href="http://amix.dk/blog/post/19574" rel="nofollow">Hacker New's ranking algorithm</a> with the code above so that older items get moved down in rank, but I am having trouble. I am not sure if the relevant code should go into the VoteAwareManager function, or the most_loved method, or elsewhere altogether.</strong> </p> <p>The following is what I have tried: </p> <p><strong>1. Calculation in most_loved method:</strong> returns <code>TypeError at / unsupported operand type(s) for -: 'QuerySet' and 'int'</code> (when using a random timestamp just to see if I can get a result, eventually I need to figure out how to get the object timestamp, too — I am a beginning programmer):</p> <pre><code>def most_loved(self): totalscore = self._get_score_annotation() time_stamp = 20120920 gravity = 1.8 return (totalscore - 1) / pow((time_stamp+2), gravity) </code></pre> <p><strong>2. Calculation in SQL:</strong> returns <code>TemplateSyntaxError at / Caught DatabaseError while rendering: column "votes.time_stamp" must appear in the GROUP BY clause or be used in an aggregate function LINE 1: ...(SELECT COALESCE(SUM(vote),0 / (EXTRACT(HOUR FROM TIME_STAMP...</code>:</p> <pre><code>class VoteAwareManager(models.Manager): """ Get top votes. hot = VoteAwareManager() """ def _get_score_annotation(self): model_type = ContentType.objects.get_for_model(self.model) table_name = self.model._meta.db_table return self.extra(select={ 'score': 'SELECT COALESCE(SUM(vote),0 / (EXTRACT(HOUR FROM TIME_STAMP)+2 * 1.8)) FROM %s WHERE content_type_id=%d AND object_id=%s.id' % (Vote._meta.db_table, int(model_type.id), table_name) } ) </code></pre> <p>One option is attempt to change the voting system to use <a href="http://code.google.com/p/django-rangevoting/" rel="nofollow">django-rangevoting</a>, but I'd like to get this working with django-voting if possible. Any help much appreciated.</p>
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