Django: is there a way to count SQL queries from an unit test?

Question

I am trying to find out the number of queries executed by a utility function. I have written a unit test for this function and the function is working well. What I would like to do is track the number of SQL queries executed by the function so that I can see if there is any improvement after some refactoring.

def do_something_in_the_database():
    # Does something in the database
    # return result

class DoSomethingTests(django.test.TestCase):
    def test_function_returns_correct_values(self):
        self.assertEqual(n, <number of SQL queries executed>)

EDIT: I found out that there is a pending Django feature request for this. However the ticket is still open. In the meantime is there another way to go about this?

Answer 1

Since Django 1.3 there is a assertNumQueries available exactly for this purpose.

One way to use it (as of Django 3.2) is as a context manager:

# measure queries of some_func and some_func2
with self.assertNumQueries(2):
    result = some_func()
    result2 = some_func2()

Answer 2

Vinay's response is correct, with one minor addition.

Django's unit test framework actually sets DEBUG to False when it runs, so no matter what you have in settings.py, you will not have anything populated in connection.queries in your unit test unless you re-enable debug mode. The Django docs explain the rationale for this as:

Regardless of the value of the DEBUG setting in your configuration file, all Django tests run with DEBUG=False. This is to ensure that the observed output of your code matches what will be seen in a production setting.

If you're certain that enabling debug will not affect your tests (such as if you're specifically testing DB hits, as it sounds like you are), the solution is to temporarily re-enable debug in your unit test, then set it back afterward:

def test_myself(self):
    from django.conf import settings
    from django.db import connection

    settings.DEBUG = True
    connection.queries = []

    # Test code as normal
    self.assert_(connection.queries)

    settings.DEBUG = False

Answer 3

If you are using pytest, pytest-django has django_assert_num_queries fixture for this purpose:

def test_queries(django_assert_num_queries):
    with django_assert_num_queries(3):
        Item.objects.create('foo')
        Item.objects.create('bar')
        Item.objects.create('baz')

Answer 4

If you don't want use TestCase (with assertNumQueries) or change settings to DEBUG=True, you can use context manager CaptureQueriesContext (same as assertNumQueries using).

from django.db import ConnectionHandler
from django.test.utils import CaptureQueriesContext

DB_NAME = "default"  # name of db configured in settings you want to use - "default" is standard
connection = ConnectionHandler()[DB_NAME]
with CaptureQueriesContext(connection) as context:
    ... # do your thing
num_queries = context.initial_queries - context.final_queries
assert num_queries == expected_num_queries

db settings