问题
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
回答1:
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.
回答2:
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.
来源：https://stackoverflow.com/questions/11073698/how-do-you-join-two-tables-using-django-without-using-raw-sql