tests.py

# $ PYTHONPATH=.. ./manage.py test
# Creating test database for alias 'default'...
# test_list_backed_lookup
# 3.81117606163
# .test_manager_backed_lookup
# 6.57371211052
# .
# ----------------------------------------------------------------------
# Ran 2 tests in 12.099s

from timeit import Timer

from django.db import models
from django.db.models import Prefetch
from django.test import TestCase


class Book(models.Model):
    title = models.CharField(max_length=100)


class Author(models.Model):
    author = models.CharField(max_length=100)
    books = models.ManyToManyField(Book)


class Benchmark(TestCase):
    def setUp(self):
        for i in range(0, 100):
            a = Author.objects.create(author="Author %s" % i)
            bset = set()
            for j in range(0, 20):
                b = Book.objects.create(title="Title %s" % j)
                bset.add(b)
            a.books = bset

    def test_manager_backed_lookup(self):
        def prefetch():
            for a in Author.objects.prefetch_related('books'):
                list(a.books.all())
        timer = Timer(prefetch)
        print('test_manager_backed_lookup')
        print(timer.timeit(number=100))

    def test_list_backed_lookup(self):
        def prefetch():
            for a in Author.objects.prefetch_related(book_list=Prefetch('books')):
                list(a.book_list)
        timer = Timer(prefetch)
        print('test_list_backed_lookup')
        print(timer.timeit(number=100))