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Code Issues 32 Releases Wiki Activity

Fixed #28312 -- Made ModelChoiceIterator.__len__() more memory-efficient.

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Instead of loading all QuerySet results in memory, count the number of
entries. This adds an extra query when list() or tuple() is called on the
choices (because both call __len__() then __iter__()) but uses less
memory since the QuerySet results won't be cached. In most cases, the
choices will only be iterated on, meaning that __len__() won't be called
and only one query will be executed.
This commit is contained in:
François Freitag
2018-04-13 18:15:22 -07:00
committed by Tim Graham
parent 9ec77f3d66
commit 3fca95e1ad
3 changed files with 25 additions and 14 deletions
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30
tests/model_forms/test_modelchoicefield.py
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@@ -96,6 +96,25 @@ class ModelChoiceFieldTests(TestCase):
(self.c3.pk, 'category Third'),
])
def test_choices_freshness(self):
f = forms.ModelChoiceField(Category.objects.all())
self.assertEqual(len(f.choices), 4)
self.assertEqual(list(f.choices), [
('', '---------'),
(self.c1.pk, 'Entertainment'),
(self.c2.pk, 'A test'),
(self.c3.pk, 'Third'),
])
c4 = Category.objects.create(name='Fourth', slug='4th', url='4th')
self.assertEqual(len(f.choices), 5)
self.assertEqual(list(f.choices), [
('', '---------'),
(self.c1.pk, 'Entertainment'),
(self.c2.pk, 'A test'),
(self.c3.pk, 'Third'),
(c4.pk, 'Fourth'),
])
def test_deepcopies_widget(self):
class ModelChoiceForm(forms.Form):
category = forms.ModelChoiceField(Category.objects.all())
@@ -257,17 +276,6 @@ class ModelChoiceFieldTests(TestCase):
(self.c3.pk, 'Third'),
])
def test_queryset_result_cache_is_reused(self):
f = forms.ModelChoiceField(Category.objects.all())
with self.assertNumQueries(1):
# list() calls __len__() and __iter__(); no duplicate queries.
self.assertEqual(list(f.choices), [
('', '---------'),
(self.c1.pk, 'Entertainment'),
(self.c2.pk, 'A test'),
(self.c3.pk, 'Third'),
])
def test_num_queries(self):
"""
Widgets that render multiple subwidgets shouldn't make more than one