ModelMultipleChoiceField inconsistently returns a list if empty.

[Stephen Burrows]

The ModelMultipleChoiceField is described as "A MultipleChoiceField whose choices are a model QuerySet." If some models have been selected, then the cleaned value of this field is a queryset. However, if the field is not required and the value is empty, the cleaned value returned is a list.

This is inconsistent and causes problems if, say, you want to check that the value passed to a method is a queryset and, if so, access queryset.model. The attached patch replaces [] with self.queryset.none(). I'll work on tests tomorrow if nobody beats me to it.

[Stephen Burrows]

The test patch is off SVN r14358, so switched the version.

[Daniel F Moisset]

Looks legitimate... taking a look at the patch to see if it's ready for checkin

[Daniel F Moisset]

I have two tests failures after applying the patch (which weren't there before):

======================================================================
FAIL: test_callable_initial_value (regressiontests.forms.models.ModelFormCallableModelDefault)
The initial value for a callable default returning a queryset is the pk (refs #13769)
----------------------------------------------------------------------
======================================================================
FAIL: test_initial_instance_value (regressiontests.forms.models.ModelFormCallableModelDefault)
Initial instances for model fields may also be instances (refs #7287)
----------------------------------------------------------------------

[Stephen Burrows]

empty_queryset_and_tests.diff corrects the failures by accounting for the changes to the forms rendered in test_callable_initial_value and test_initial_instance_value caused by the additional field on ChoiceFieldModel which was introduced in my previous patch. I've run the regression test suite this time and have no unexpected failures. I can continue working on this if there's anything else to do for it.

[Stephen Burrows]

Updated the patch to r14864 to account for changes in file structure. The full test suite passes.

[Stephen Burrows]

Updated empty_queryset_and_tests_r14864.diff to include necessary documentation changes. Note that as things stand, the documentation is already incorrect: it claims that ModelMultipleChoiceField normalizes to a list, when in fact it normalizes to a QuerySet.

[Stephen Burrows]

Added git branch for this ticket @ ​http://github.com/melinath/django/tree/ticket14567. The patch is still current as of r15353.

[Stephen Burrows]

Incidentally, I don't get any extra test failures with the patch.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Stephen Burrows]

I've updated the patch to apply to the latest develop and opened a pull request: ​https://github.com/django/django/pull/398.

[Anssi Kääriäinen]

To me it seems this needs a minor note as a backwards incompatible change. In any case, this is a change we should do. The return value should always be of consistent type (that is, a queryset). The docs aren't exactly accurate currently anyways as of the return value.

I will take care of committing this.

[Anssi Kääriäinen <akaariai@…>]

In 218abcc9e550d266a9979e10f562fc21b8f34c6a:

Fixed #14567 -- Made ModelMultipleChoiceField return EmptyQuerySet as empty value

[Anssi Kääriäinen]

Committed with some docs additions and some changes to the tests to avoid even larger HTML output comparisons.

[Carl Meyer <carl@…>]

In a98465c040319b74b697bace11da5b13cc42427f:

Refs #14567 -- Fixed failing test that wasn't being run.