Django annotate with aggregated average value

Question

In the following example from django documentation, how to get

Publisher.objects.all()

annotated with field average_rating computed using average of book ratings and max_rating computed using maximum rating of books?

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()

class Publisher(models.Model):
    name = models.CharField(max_length=300)
    num_awards = models.IntegerField()

class Book(models.Model):
    name = models.CharField(max_length=300)
    pages = models.IntegerField()
    price = models.DecimalField(max_digits=10, decimal_places=2)
    rating = models.FloatField()
    authors = models.ManyToManyField(Author)
    publisher = models.ForeignKey(Publisher)
    pubdate = models.DateField()

class Store(models.Model):
    name = models.CharField(max_length=300)
    books = models.ManyToManyField(Book)
    registered_users = models.PositiveIntegerField()

Precisely I should be able to print something like this after the queryset:

for p in Publisher.objects.all().annotate(...):
    print p, p.average_rating, p.max_rating

Eugene Soldatov · Accepted Answer · 2015-10-01 11:24:09Z

1

You can access books of publisher using book__rating like this:

Publisher.objects.annotate(average_rating=Avg('book__rating'), max_rating=Max('book__rating'))

edited Oct 1, 2015 at 11:24

answered Oct 1, 2015 at 9:32

Eugene Soldatov

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1 Comment

Bharathwaaj Over a year ago

FieldError: Cannot resolve keyword 'books_set' into field. Choices are: book, id, name, num_awards

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