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

django/forms/models.py

@@ -1013,7 +1013,7 @@ class ModelMultipleChoiceField(ModelChoiceField):
         if self.required and not value:
             raise ValidationError(self.error_messages['required'])
         elif not self.required and not value:
-            return []
+            return self.queryset.none()
         if not isinstance(value, (list, tuple)):
             raise ValidationError(self.error_messages['list'])
         key = self.to_field_name or 'pk'

docs/ref/forms/fields.txt

@@ -997,13 +997,17 @@ objects (in the case of ``ModelMultipleChoiceField``) into the
 .. class:: ModelMultipleChoiceField(**kwargs)
 
     * Default widget: ``SelectMultiple``
-    * Empty value: ``[]`` (an empty list)
+    * Empty value: An empty ``QuerySet`` (self.queryset.none())
-    * Normalizes to: A list of model instances.
+    * Normalizes to: A ``QuerySet`` of model instances.
     * Validates that every id in the given list of values exists in the
       queryset.
     * Error message keys: ``required``, ``list``, ``invalid_choice``,
       ``invalid_pk_value``
 
+    .. versionchanged:: 1.5
+        The empty and normalized values were changed to be consistently
+        ``QuerySets`` instead of ``[]`` and ``QuerySet`` respectively.
+
     Allows the selection of one or more model objects, suitable for
     representing a many-to-many relation. As with :class:`ModelChoiceField`,
     you can use ``label_from_instance`` to customize the object

docs/releases/1.5.txt

@@ -422,6 +422,9 @@ on the form.
 Miscellaneous
 ~~~~~~~~~~~~~
 
+* :class:`django.forms.ModelMultipleChoiceField` now returns an empty
+  ``QuerySet`` as the empty value instead of an empty list.
+
 * :func:`~django.utils.http.int_to_base36` properly raises a :exc:`TypeError`
   instead of :exc:`ValueError` for non-integer inputs.
 

tests/modeltests/model_forms/tests.py

@@ -8,6 +8,7 @@ from django import forms
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.core.validators import ValidationError
 from django.db import connection
+from django.db.models.query import EmptyQuerySet
 from django.forms.models import model_to_dict
 from django.utils.unittest import skipUnless
 from django.test import TestCase
@@ -1035,8 +1036,8 @@ class OldFormForXTests(TestCase):
             f.clean([c6.id])
 
         f = forms.ModelMultipleChoiceField(Category.objects.all(), required=False)
-        self.assertEqual(f.clean([]), [])
+        self.assertIsInstance(f.clean([]), EmptyQuerySet)
-        self.assertEqual(f.clean(()), [])
+        self.assertIsInstance(f.clean(()), EmptyQuerySet)
         with self.assertRaises(ValidationError):
             f.clean(['10'])
         with self.assertRaises(ValidationError):

tests/regressiontests/forms/models.py

@@ -63,6 +63,12 @@ class ChoiceFieldModel(models.Model):
     multi_choice_int = models.ManyToManyField(ChoiceOptionModel, blank=False, related_name='multi_choice_int',
                                               default=lambda: [1])
 
+class OptionalMultiChoiceModel(models.Model):
+    multi_choice = models.ManyToManyField(ChoiceOptionModel, blank=False, related_name='not_relevant',
+                                          default=lambda: ChoiceOptionModel.objects.filter(name='default'))
+    multi_choice_optional = models.ManyToManyField(ChoiceOptionModel, blank=True, null=True,
+                                                   related_name='not_relevant2')
+
 
 class FileModel(models.Model):
     file = models.FileField(storage=temp_storage, upload_to='tests')

tests/regressiontests/forms/tests/models.py

@@ -11,7 +11,7 @@ from django.test import TestCase
 from django.utils import six
 
 from ..models import (ChoiceOptionModel, ChoiceFieldModel, FileModel, Group,
-    BoundaryModel, Defaults)
+    BoundaryModel, Defaults, OptionalMultiChoiceModel)
 
 
 class ChoiceFieldForm(ModelForm):
@@ -19,6 +19,11 @@ class ChoiceFieldForm(ModelForm):
         model = ChoiceFieldModel
 
 
+class OptionalMultiChoiceModelForm(ModelForm):
+    class Meta:
+        model = OptionalMultiChoiceModel
+
+
 class FileForm(Form):
     file1 = FileField()
 
@@ -34,6 +39,21 @@ class TestTicket12510(TestCase):
             field = ModelChoiceField(Group.objects.order_by('-name'))
             self.assertEqual('a', field.clean(self.groups[0].pk).name)
 
+
+class TestTicket14567(TestCase):
+    """
+    Check that the return values of ModelMultipleChoiceFields are QuerySets
+    """
+    def test_empty_queryset_return(self):
+        "If a model's ManyToManyField has blank=True and is saved with no data, a queryset is returned."
+        form = OptionalMultiChoiceModelForm({'multi_choice_optional': '', 'multi_choice': ['1']})
+        self.assertTrue(form.is_valid())
+        # Check that the empty value is a QuerySet
+        self.assertTrue(isinstance(form.cleaned_data['multi_choice_optional'], models.query.QuerySet))
+        # While we're at it, test whether a QuerySet is returned if there *is* a value.
+        self.assertTrue(isinstance(form.cleaned_data['multi_choice'], models.query.QuerySet))
+
+
 class ModelFormCallableModelDefault(TestCase):
     def test_no_empty_option(self):
         "If a model's ForeignKey has blank=False and a default, no empty option is created (Refs #10792)."
@@ -103,7 +123,6 @@ class ModelFormCallableModelDefault(TestCase):
 <input type="hidden" name="initial-multi_choice_int" value="3" id="initial-id_multi_choice_int_1" /> <span class="helptext"> Hold down "Control", or "Command" on a Mac, to select more than one.</span></p>""")
 
 
-
 class FormsModelTestCase(TestCase):
     def test_unicode_filename(self):
         # FileModel with unicode filename and data #########################