#29159: ModelChoiceIterator triggers duplicate queries when choices are cast to
               Reporter:  Fran├žois   |          Owner:  Fran├žois Freitag
  Freitag                            |
                   Type:             |         Status:  assigned
  Uncategorized                      |
              Component:  Forms      |        Version:  1.8
               Severity:  Normal     |       Keywords:
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
 When there are no `prefetch_related()` on `ModelChoiceIterator`'s
 queryset, it attempts to use the `iterator()` method to avoid loading all
 choices in memory.
 related because iterator() and prefetch_related() don't make sense

 That results in a duplicate query if the choices have been evaluated
 before, because calling `iterator()` will clone the `QuerySet`, resetting
 its result cache in the process.

 class TestModelChoiceField(TestCase):
     def test_queryset_result_cache_is_reused(self):
         choice = ChoiceOptionModel.objects.create(name="choice 1")
         f = ModelChoiceField(ChoiceOptionModel.objects.all())
         with self.assertNumQueries(1):
                 # list calls both __len__ and __iter__
                 [('', '---------'), (choice.pk, str(choice))],

 Fails with:
 FAIL: test_queryset_result_cache_is_reused
 Traceback (most recent call last):
   File "django/tests/forms_tests/test_tmp.py", line 19, in
     [('', '---------'), (choice.pk, str(choice))],
   File "django/django/test/testcases.py", line 80, in __exit__
     '%d. %s' % (i, query['sql']) for i, query in
 enumerate(self.captured_queries, start=1)
 AssertionError: 2 != 1 : 2 queries executed, 1 expected
 Captured queries were:
 1. SELECT "forms_tests_choiceoptionmodel"."id",
 "forms_tests_choiceoptionmodel"."name" FROM
 "forms_tests_choiceoptionmodel" ORDER BY
 "forms_tests_choiceoptionmodel"."name" ASC
 2. SELECT "forms_tests_choiceoptionmodel"."id",
 "forms_tests_choiceoptionmodel"."name" FROM
 "forms_tests_choiceoptionmodel" ORDER BY
 "forms_tests_choiceoption$odel"."name" ASC

Ticket URL: <https://code.djangoproject.com/ticket/29159>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

You received this message because you are subscribed to the Google Groups 
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to django-updates+unsubscr...@googlegroups.com.
To post to this group, send email to django-updates@googlegroups.com.
To view this discussion on the web visit 
For more options, visit https://groups.google.com/d/optout.

Reply via email to