[Answer]-How to get number of items grouped by a property of an intermediate model

To do what you’re trying to achieve in one query, you need to use Count, annotate and values_list

I’ll show you a code example and then I’ll try to explain it:

from django.db.models import Count
from your_project.models import *

Genre.objects.all().values_list('name').annotate(num_books=Count('book'))

1. .values_list('name'): This return a list of all genres by name
2. .annotate(num_books=Count('book')): This count books for each Genre

I have a similar models structure in my projects and when I execute that code, I get this as answer:

[(u'GENRE_NAME', 13), (u'GENRE_NAME', 14), (u'GENRE_NAME', 0),...]

You can parse the output of this query to fit your expectations

I also recomend you to check oficial documentation Django Agreggation

This loops over all your genres and prints out how many of them there are.
Even if there are 0 in a genre.

for a_genre in Gendre.objects.all():
    print Book.objects.filter(genre=a_genre).count()

and if you want it printed with the genre aswel

for a_genre in Gendre.objects.all():
    print "%s (%d)" % (a_genre, Book.objects.filter(genre=a_genre).count())

Documentation for filters in django : https://docs.djangoproject.com/en/1.7/topics/db/queries/#retrieving-specific-objects-with-filters