Commit e44ab5bb authored by Anton I. Sipos's avatar Anton I. Sipos
Browse files

Fixed #18949 -- Improve performance of model_to_dict with many-to-many 

When calling model_to_dict, improve performance of the generated SQL by
using values_list to determine primary keys of many to many objects. Add
a specific test for this function, test_model_to_dict_many_to_many

Thanks to brian for the original report and suggested fix.
parent 8d3f932f

django/forms/models.py

+1 −1
Original line number Diff line number Diff line
@@ -126,7 +126,7 @@ def model_to_dict(instance, fields=None, exclude=None): 
                data[f.name] = []

            else:

                # MultipleChoiceWidget needs a list of pks, not object instances.

                data[f.name] = [obj.pk for obj in f.value_from_object(instance)]

                data[f.name] = list(f.value_from_object(instance).values_list('pk', flat=True))

        else:

            data[f.name] = f.value_from_object(instance)

    return data

tests/modeltests/model_forms/tests.py

+36 −0
Original line number Diff line number Diff line
@@ -561,6 +561,42 @@ class UniqueTest(TestCase): 
            "slug": "Django 1.0"}, instance=p)

        self.assertTrue(form.is_valid())



class ModelToDictTests(TestCase):

    """

    Tests for forms.models.model_to_dict

    """

    def test_model_to_dict_many_to_many(self):

        categories=[

            Category(name='TestName1', slug='TestName1', url='url1'),

            Category(name='TestName2', slug='TestName2', url='url2'),

            Category(name='TestName3', slug='TestName3', url='url3')

        ]

        for c in categories:

            c.save()

        writer = Writer(name='Test writer')

        writer.save()



        art = Article(

            headline='Test article',

            slug='test-article',

            pub_date=datetime.date(1988, 1, 4),

            writer=writer,

            article='Hello.'

        )

        art.save()

        for c in categories:

            art.categories.add(c)

        art.save()



        with self.assertNumQueries(1):

            d = model_to_dict(art)



        #Ensure all many-to-many categories appear in model_to_dict

        for c in categories:

            self.assertIn(c.pk, d['categories'])

        #Ensure many-to-many relation appears as a list

        self.assertIsInstance(d['categories'], list)



class OldFormForXTests(TestCase):

    def test_base_form(self):

        self.assertEqual(Category.objects.count(), 0)