Methods for comparison of Django Q objects

[stevekm]

In your page here:

https://jamescooke.info/comparing-django-q-objects.html

https://github.com/jamescooke/blog/blob/d31e4ef3abed4985fa9cc9c567590e9cdfda13b4/content/1603-comparing-django-q-objects.rst

On the discussion of how to compare Q objects in Django unit tests, there are some alternative methods that can be used which you do not cover.

Here are some examples where you can test the contents of a Django Q object for single Q objects, compound AND/OR Q objects, and you can also test the contents of a Q object in case you have a situation where the order of the results are non-deterministic (e.g. you are using a set to hold some values that build the object).

In these examples, the Q object is being returned by an external query builder function based on a list of values.

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

class TestRetrieveSamplesByQuery(TestCase):
    def test_single_query(self):
        values = ["foo"]

        query = function_that_returns_Q_object(values)
        # (AND: (('value', 'bar'))

        expected_query = Q(value='bar')
        self.assertEqual(query, expected_query)

    def test_multiple_queries(self):
        values = ["foo", "bar"]

        query = function_that_returns_Q_object(values)
        # (OR: ('value', 'baz'), ('value', 'bar'))

        expected_query = Q(value='bar') | Q(value='baz')
        self.assertEqual(query, expected_query)

    def test_multiple_queries_indeterminate_order(self):
        values = ["foo", "bar"]

        query = another_function_that_returns_Q_object(values)
        # might return either:
        # (OR: ('value', 'baz'), ('value', 'bar'))
        # or: 
        # (OR: ('value', 'bar'), ('value', 'baz'))

        # query.__dict__
        # {'children': [('value', 'baz'), ('value', 'bar')], 'connector': 'OR', 'negated': False}

        self.assertTrue( ('value', 'baz') in query.__dict__['children'] )
        self.assertTrue( ('value', 'bar') in query.__dict__['children'] )
        self.assertEqual( len(query.__dict__['children']), 2 )
        self.assertTrue( query.__dict__['connector'] == 'OR' )
        self.assertTrue( query.__dict__['negated'] == False )

[jamescooke]

Thanks @stevekm for the comments.

What version of Django are you using? These posts were written about the time of Django 1.8 when Q objects did not implement __cmp__ and so using assertEqual() would not work - hence the reason for the post.