Django count on many-to-many - django

Question

I have the models:
class Article(models.Model):
title = models.TextField(blank=True)
keywords = models.ManyToManyField(Keyword, null=True, blank=True)
class Keyword(models.Model):
keyword = models.CharField(max_length=355, blank=True)
I want to get a count of how many articles have each keyword. In essence I want to have a list of keywords where I can get each ones count to give it a relative weighting.
I have tried:
keyword_list=Article.objects.all().annotate(key_count=Count('keywords__keyword'))
but
keyword_list[0].key_count
just seems to give me the number of different keywords each article has? Is it somehow a reverse lookup?
Any help would be much appreciated.
UPDATE
So I got it working:
def keyword_list(request):
MAX_WEIGHT = 5
keywords = Keyword.objects.order_by('keyword')
for keyword in keywords:
keyword.count = Article.objects.filter(keywords=keyword).count()
min_count = max_count = keywords[0].count
for keyword in keywords:
if keyword.count < min_count:
min_count = keyword.count
if max_count > keyword.count:
max_count = keyword.count
range = float(max_count - min_count)
if range == 0.0:
range = 1.0
for keyword in keywords:
keyword.weight = (
MAX_WEIGHT * (keyword.count - min_count) / range
)
return { 'keywords': keywords }
but the view results in a hideous number of queries. I have tried implementing the suggestions given here (thanks) but this is the only methid which seems to work at the moment. However, I must be doing something wrong as I now have 400+ queries!
UPDATE
Wooh! Finally got it working:
def keyword_list(request):
MAX_WEIGHT = 5
keywords_with_article_counts = Keyword.objects.all().annotate(count=Count('keyword_set'))
# get keywords and count limit to top 20 by count
keywords = keywords_with_article_counts.values('keyword', 'count').order_by('-count')[:20]
min_count = max_count = keywords[0]['count']
for keyword in keywords:
if keyword['count'] < min_count:
min_count = keyword['count']
if max_count < keyword['count']:
max_count = keyword['count']
range = float(max_count - min_count)
if range == 0.0:
range = 1.0
for keyword in keywords:
keyword['weight'] = int(
MAX_WEIGHT * (keyword['count'] - min_count) / range
)
return { 'keywords': keywords}

Answer 1

Since you want the number of articles that have each keyword, you have to do it the other way:
>>> Keyword.objects.all().annotate(article_count=models.Count('article'))[0].article_count
2

Answer 2

This is the same as the answer from Vebjorn Ljosa, but with a little context, where article_set is the related_name of the reverse many-to-many relationship object.
keywords_with_article_counts = Keyword.objects.all().annotate(article_count=Count('article_set'))
To illustrate your results, it would be easier to return the .values():
keywords_with_article_counts.values('keyword', 'article_count')
Which would return a list of dictionaries that would look something like this:
[{'article_count': 36, 'keyword': u'bacon'},
{'article_count': 4, 'keyword': u'unicorns'},
{'article_count': 8, 'keyword': u'python'}]

Answer 3

i don't know how you would do it efficiently but if you need to get it done.
keywords = Keyword.objects.all()
for keyword in keywords:
print 'Total Articles: %d' % (Article.objects.filter(keywords=keyword).count())