Django: is there a way to count SQL queries from an unit test?
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12-09-2019 - |
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?
Solution
Since Django 1.3 there is a assertNumQueries available exactly for this purpose.
OTHER TIPS
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
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')
If you have DEBUG
set to True in your settings.py
(presumably so in your test environment) then you can count queries executed in your test as follows:
from django.db import connection
class DoSomethingTests(django.test.TestCase):
def test_something_or_other(self):
num_queries_old = len(connection.queries)
do_something_in_the_database()
num_queries_new = len(connection.queries)
self.assertEqual(n, num_queries_new - num_queries_old)
In modern Django (>=1.8) it's well documented (it's also documented for 1.7) here, you have the method reset_queries instead of assigning connection.queries=[] which indeed is raising an error, something like that works on django>=1.8:
class QueriesTests(django.test.TestCase):
def test_queries(self):
from django.conf import settings
from django.db import connection, reset_queries
try:
settings.DEBUG = True
# [... your ORM code ...]
self.assertEquals(len(connection.queries), num_of_expected_queries)
finally:
settings.DEBUG = False
reset_queries()
You may also consider resetting queries on setUp/tearDown to ensure queries are reset for each test instead of doing it on finally clause, but this way is more explicit (although more verbose), or you can use reset_queries in the try clause as many times as you need to evaluate queries counting from 0.
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