How do you join two tables using Django without using raw sql?

Is is possible to programatically join two tables using Django's ORM? I have two models: Topics and Votes. On my template I have a list of topics that users can up/down vote like Reddit. Everything works as it should except for sorting the results. I cannot figure out how to sort an objects list based off the score which is a sum of each object's vote count. I can retrieve the desired data from postgres without any issue:

select i.id, i.title, i.date_created, s.object_id, s.vote, Sum(vote) 
from topic_topic i, votes s 
where i.id = s.object_id 
group by 1, 2, 3, 4, 5 
order by sum DESC;

It returns the desired results:

id | title  |         date_created          | object_id | vote | sum 

11 | sdfg   | 2012-06-04 23:30:17.805671-07 |        11 |    1 |   2

 1 | test   | 2012-05-13 17:03:24.206092-07 |         1 |    1 |   2

 3 | asdf   | 2012-05-13 19:23:15.059135-07 |         3 |    1 |   2

 2 | adsf   | 2012-05-13 19:21:34.180905-07 |         2 |    1 |   2

12 | 11     | 2012-06-04 23:30:54.759158-07 |        12 |    1 |   2

 9 | asfd   | 2012-05-24 00:26:26.705843-07 |         9 |   -1 |  -1

 4 | asdf   | 2012-05-14 19:59:52.450693-07 |         4 |   -1 |  -2

The problem is, I am not sure how to retrieve this as a queryset. At the moment I am using the following to display objects:

topic_list = Topic.objects.all()

Everything displays as I would like it to, except for the sort order. I would like the highest score to display first.

Resources I have already looked at: https://docs.djangoproject.com/en/dev/topics/db/managers/#adding-extra-manager-methods How to query as GROUP BY in django?

And many more, but as a new user, anti-spam prevents me from adding them.

Thing's I've tried:

Chain:

listed_links = list(chain(topic, score))

Unfortunately, if I tried to add a sorted value this broke.

Combining object lists:

topic = Topic.objects.all().values_list('user','id', 'title','slug', 'date_created', 'date_updated',)

score = Vote.objects.values('object_id').annotate(total=Sum('vote')).order_by('-total')

results = []

for topic in topic:
results.append(topic)

for score in score:
results.append(topic)

This resulted in all the objects I wanted in one list, but I could not figure out how to link topic.id to score.object_id.

I've also tried inserting raw SQL, but I don't feel like I am doing it correctly, and could lead to SQL injection by a third party.

I would love to share the results of this back to the django-voting project. Like I said, everything works as it should, except I cannot figure out how to sort by score desc.

=============Voting========================

from django.contrib.contenttypes import generic

from django.contrib.contenttypes.models import ContentType

from django.contrib.auth.models import User

from django.db import models

from voting.managers import VoteManager

from voting.VotedObjectsManager import VotedObjectsManager

    SCORES = (
    (+1, u'+1'),
    (-1, u'-1'),
)

class Vote(models.Model):

    """
    A vote on an object by a User.
    """

    user         = models.ForeignKey(User)

    content_type = models.ForeignKey(ContentType)

    object_id    = models.PositiveIntegerField()

    object       = generic.GenericForeignKey('content_type', 'object_id')

    vote         = models.SmallIntegerField(choices=SCORES)

    objects      = VoteManager()


    class Meta:
        db_table = 'votes'
        # One vote per user per object
        unique_together = (('user', 'content_type', 'object_id'),)

    def __unicode__(self):
        return u'%s: %s on %s' % (self.user, self.vote, self.object)

    def is_upvote(self):
        return self.vote == 1

    def is_downvote(self):
        return self.vote == -1

=============Topic Model========================

from django.db import models

from datetime import datetime

from tinymce import models as tinymce_models

from django.forms import ModelForm

from django.template.defaultfilters import slugify

from tagging.fields import TagField

from tagging.models import Tag

from django.contrib.auth.models import User

from django.utils.translation import ugettext_lazy as _

from django.contrib.contenttypes.models import ContentType

from django.contrib.contenttypes import generic

from django.core import urlresolvers

    class Topic(models.Model):

    title           = models.CharField(max_length=50)

    slug            = models.SlugField(max_length=50, editable=False)

    topic         = tinymce_models.HTMLField()

    date_created    = models.DateTimeField(editable=False)

    date_updated    = models.DateTimeField(editable=False)

    tags            = TagField()


    def set_tags(self, tags):
        Tag.objects.update_tags(self, tags)    

    def __unicode__(self):
        return self.tags

    def __unicode__(self):
        return self.id

    def __unicode__(self):
        return self.title

Answers


I was able to figure out the solution using a patch as described here:

http://code.google.com/p/django-voting/issues/detail?id=10

The difference was that I extracted the following lines:

    def select_score(self):
    """ Add vote scores for objects in resoultset """
    from django.contrib.contenttypes.models import ContentType
    model_type = ContentType.objects.get_for_model(self.model)
    table_name = self.model._meta.db_table
    print type(model_type)
    print model_type.id
    return self.extra(select={'score': 'SELECT SUM(vote) FROM votes WHERE content_type_id=%i AND object_id=%s.id' % (int(model_type.id), table_name)})

And added them to the voting/managers.py file as so:

class VoteManager(models.Manager):
def get_score(self, obj):
    """
    Get a dictionary containing the total score for ``obj`` and
    the number of votes it's received.
    """
    ctype = ContentType.objects.get_for_model(obj)
    result = self.filter(object_id=obj._get_pk_val(),
                         content_type=ctype).extra(
        select={
            'score': 'COALESCE(SUM(vote), 0)',
            'num_votes': 'COALESCE(COUNT(vote), 0)',
    }).values_list('score', 'num_votes')[0]

    return {
        'score': int(result[0]),
        'num_votes': int(result[1]),
    }

Then In my topic.views.py I added the following:

from voting.managers import VoteManager
def index(request):
queryset = Topic.objects.select_score().order_by('-score')
paginator = Paginator(queryset, 3) # Show 25 contacts per page

page = request.GET.get('page')
try:
    topic_list = paginator.page(page)
except PageNotAnInteger:
    # If page is not an integer, deliver first page.
    topic_list = paginator.page(1)
except EmptyPage:
    #If page is out of range (e.g. 9999), deliver last page of results.
    topic_list = paginator.page(paginator.num_pages)

c = Context({
'topic_list': topic_list,
'request': request
})
return render_to_response('idea/index.html', c, context_instance=RequestContext(request))

Lastly, in my index.html I added the following lines slightly deviating from the original example provided for users:

{% load voting_tags %}
{% votes_by_user user on topic_list as vote_dict %}
{% scores_for_objects topic_list as score_dict %}

<table id="voting_table" class="list">
<tbody>
  {% for link in topic_list %}
<td class="vote">

{% dict_entry_for_item link from vote_dict as vote %}
{% dict_entry_for_item link from score_dict as score %}

<div>    
 <form class="linkvote" id="linkup{{ link.id }}"{% if vote and vote.is_upvote %} action="{% url link_vote object_id=link.id, direction="clear" %}"{% else %} action="{% url link_vote object_id=link.id, direction="up" %}"{% endif %} method="POST">
    <input type="image" id="linkuparrow{{ link.id }}" src="{{ STATIC_URL }}images/aup{% if vote and vote.is_upvote %}mod{% else %}grey{% endif %}.png">
    {% csrf_token %}
    <input type="hidden" name="next" value="{{ request.get_full_path }}"/>
    {% else %}

  </form>

       <div id="link_score">{{ score.score|default:0 }}</div>

  <form class="linkvote" id="linkdown{{ link.id }}" {% if vote and vote.is_downvote %} action="{% url link_vote object_id=link.id, direction="clear" %}"{% else %} action="{% url link_vote object_id=link.id, direction="down" %}"{% endif %} method="POST">
  {% csrf_token %}
    <input type="image" id="linkdownarrow{{ link.id }}" src="{{ STATIC_URL }}images/adown{% if vote and vote.is_downvote %}mod{% else %}grey{% endif %}.png">
     <input type="hidden" name="next" value="{{ request.get_full_path }}"/>

</td>
<td class="item">
  <a id="link_title" href="{{ link.id }}">{{ link.title|escape }}</a></h2>
  <p class="details">
    <span class="score" id="linkscore{{ link.id }}"
          title="after {{ score.num_votes|default:0 }} vote{{ score.num_votes|default:0|pluralize }}">
    </span>
    posted {{ link.date_created|timesince }} ago by
    <span class="user"><a href="../users/{{ link.user.id }}/">{{ link.owner|escape }}</a></span>
{% get_comment_count for link as comment_count %}
    <span id="comment_score" class="comment_details"> {{ comment_count }} comment{{ comment_count|pluralize }}</span>
  </p>
</td>
</tr>{% endfor %}
</tbody>
  <td>
    <div id="paginator" class="pagination">
    <span class="step-links">
        {% if topic_list.has_previous %}
            <a href="?page={{ topic_list.previous_page_number }}">previous</a>
    {% endif %}
    {% if topic_list.has_next %}
        <a href="?page={{ topic_list.next_page_number }}">next</a>
    {% endif %}
    </span>
    </div>
  </td>
</table>

EDIT

I almost forgot! If you would like the list to sort in an order like 2,1,0,-1,-2 make sure to set the vote object value upon submitting whatever object you are creating. The example below is from my topic.views.py.

def submit_topic(request):

if request.method == 'POST':
    post_topic = PosttopicForm(request.POST)
    owner = request.user
    if post_topic.is_valid():
        topic = post_topic.save(commit=False)
        topic.owner = request.user
        topic.save()
        vote = Vote(vote='0', user = request.user, content_type_id=10, object_id=topic.pk)
        vote.save()
        url = reverse('topic', args=[topic.pk, topic.slug])
        return HttpResponseRedirect(url)
else:
    post_topic = PosttopicForm()

c = Context({
    'form': post_topic,
    'user': request.user,
    'request': request,

})

return render_to_response('topic/submit.html', c, context_instance=RequestContext(request))

I really hopes this helps someone else. Sorry for not posting the solution sooner. Hopefully someone can improve this by getting rid of the SQL all together from the VoteManager, but I need to move forward.


You could try annotating the Topic queryset to contain the sum of the votes:

topic_list = Topic.objects.all().annotate(total=Sum('vote__vote')).order_by('-total')

Note: Without seeing your models, I'm not sure what to put in the Sum() function. It should be the child model name (which I assume is vote) followed by the field name on the model.


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