[1.10.x] Fixed #27186 -- Fixed model form default fallback for MultiWidget, FileInput, SplitDateTimeWidget, SelectDateWidget, and SplitArrayWidget.

Thanks Matt Westcott for the review.

Backport of 3507d4e773 from master

django/contrib/postgres/forms/array.py

@@ -103,6 +103,12 @@ class SplitArrayWidget(forms.Widget):
         return [self.widget.value_from_datadict(data, files, '%s_%s' % (name, index))
                 for index in range(self.size)]
 
+    def value_omitted_from_data(self, data, files, name):
+        return all(
+            self.widget.value_omitted_from_data(data, files, '%s_%s' % (name, index))
+            for index in range(self.size)
+        )
+
     def id_for_label(self, id_):
         # See the comment for RadioSelect.id_for_label()
         if id_:

django/forms/models.py

@@ -54,8 +54,8 @@ def construct_instance(form, instance, fields=None, exclude=None):
             continue
         # Leave defaults for fields that aren't in POST data, except for
         # checkbox inputs because they don't appear in POST data if not checked.
-        if (f.has_default() and form.add_prefix(f.name) not in form.data and
+        if (f.has_default() and
-                not getattr(form[f.name].field.widget, 'dont_use_model_field_default_for_empty_data', False)):
+                form[f.name].field.widget.value_omitted_from_data(form.data, form.files, form.add_prefix(f.name))):
             continue
         # Defer saving file-type fields until after the other fields, so a
         # callable upload_to can use the values from other fields.

django/forms/widgets.py

@@ -237,6 +237,9 @@ class Widget(six.with_metaclass(RenameWidgetMethods)):
         """
         return data.get(name)
 
+    def value_omitted_from_data(self, data, files, name):
+        return name not in data
+
     def id_for_label(self, id_):
         """
         Returns the HTML ID attribute of this Widget for use by a <label>,
@@ -350,6 +353,9 @@ class FileInput(Input):
         "File widgets take data from FILES, not POST"
         return files.get(name)
 
+    def value_omitted_from_data(self, data, files, name):
+        return name not in files
+
 
 FILE_INPUT_CONTRADICTION = object()
 
@@ -480,10 +486,6 @@ def boolean_check(v):
 
 
 class CheckboxInput(Widget):
-    # Don't use model field defaults for fields that aren't in POST data,
-    # because checkboxes don't appear in POST data if not checked.
-    dont_use_model_field_default_for_empty_data = True
-
     def __init__(self, attrs=None, check_test=None):
         super(CheckboxInput, self).__init__(attrs)
         # check_test is a callable that takes a value and returns True
@@ -511,6 +513,11 @@ class CheckboxInput(Widget):
             value = values.get(value.lower(), value)
         return bool(value)
 
+    def value_omitted_from_data(self, data, files, name):
+        # HTML checkboxes don't appear in POST data if not checked, so it's
+        # never known if the value is actually omitted.
+        return False
+
 
 class Select(Widget):
     allow_multiple_selected = False
@@ -871,6 +878,12 @@ class MultiWidget(Widget):
     def value_from_datadict(self, data, files, name):
         return [widget.value_from_datadict(data, files, name + '_%s' % i) for i, widget in enumerate(self.widgets)]
 
+    def value_omitted_from_data(self, data, files, name):
+        return all(
+            widget.value_omitted_from_data(data, files, name + '_%s' % i)
+            for i, widget in enumerate(self.widgets)
+        )
+
     def format_output(self, rendered_widgets):
         """
         Given a list of rendered widgets (as strings), returns a Unicode string
@@ -1056,6 +1069,12 @@ class SelectDateWidget(Widget):
                 return '%s-%s-%s' % (y, m, d)
         return data.get(name)
 
+    def value_omitted_from_data(self, data, files, name):
+        return not any(
+            ('{}_{}'.format(name, interval) in data)
+            for interval in ('year', 'month', 'day')
+        )
+
     def create_select(self, name, field, value, val, choices, none_value):
         if 'id' in self.attrs:
             id_ = self.attrs['id']

docs/ref/forms/widgets.txt

@@ -271,6 +271,21 @@ foundation for custom widgets.
         customize it and add expensive processing, you should implement some
         caching mechanism yourself.
 
+    .. method:: value_omitted_from_data(data, files, name)
+
+        .. versionadded:: 1.10.2
+
+        Given ``data`` and ``files`` dictionaries and this widget's name,
+        returns whether or not there's data or files for the widget.
+
+        The method's result affects whether or not a field in a model form
+        :ref:`falls back to its default <topics-modelform-save>`.
+
+        A special case is :class:`~django.forms.CheckboxInput`, which always
+        returns ``False`` because an unchecked checkbox doesn't appear in the
+        data of an HTML form submission, so it's unknown whether or not the
+        user actually submitted a value.
+
 ``MultiWidget``
 ---------------
 

docs/releases/1.10.2.txt

@@ -17,3 +17,8 @@ Bugfixes
 
 * Disabled system check for URL patterns beginning with a '/' when
   ``APPEND_SLASH=False`` (:ticket:`27238`).
+
+* Fixed model form ``default`` fallback for ``MultiWidget``, ``FileInput``,
+  ``SplitDateTimeWidget``, ``SelectDateWidget``, and ``SplitArrayWidget``
+  (:ticket:`27186`). Custom widgets affected by this issue may need to
+  implement a :meth:`~django.forms.Widget.value_omitted_from_data` method.

docs/topics/forms/modelforms.txt

@@ -299,6 +299,8 @@ to the ``error_messages`` dictionary of the ``ModelForm``’s inner ``Meta`` cla
                 }
             }
 
+.. _topics-modelform-save:
+
 The ``save()`` method
 ---------------------
 
@@ -333,11 +335,11 @@ doesn't validate -- i.e., if ``form.errors`` evaluates to ``True``.
 If an optional field doesn't appear in the form's data, the resulting model
 instance uses the model field :attr:`~django.db.models.Field.default`, if
 there is one, for that field. This behavior doesn't apply to fields that use
-:class:`~django.forms.CheckboxInput` (or any custom widget with
+:class:`~django.forms.CheckboxInput` (or any custom widget whose
-``dont_use_model_field_default_for_empty_data=True``) since an unchecked
+:meth:`~django.forms.Widget.value_omitted_from_data` method always returns
-checkbox doesn't appear in the data of an HTML form submission. Use a custom
+``False``) since an unchecked checkbox doesn't appear in the data of an HTML
-form field or widget if you're designing an API and want the default fallback
+form submission. Use a custom form field or widget if you're designing an API
-for a ``BooleanField``.
+and want the default fallback for a :class:`~django.db.models.BooleanField`.
 
 .. versionchanged:: 1.10.1
 
@@ -345,6 +347,10 @@ for a ``BooleanField``.
     :class:`~django.forms.CheckboxInput` which means that unchecked checkboxes
     receive a value of ``True`` if that's the model field default.
 
+.. versionchanged:: 1.10.2
+
+    The :meth:`~django.forms.Widget.value_omitted_from_data` method was added.
+
 This ``save()`` method accepts an optional ``commit`` keyword argument, which
 accepts either ``True`` or ``False``. If you call ``save()`` with
 ``commit=False``, then it will return an object that hasn't yet been saved to

tests/forms_tests/widget_tests/test_checkboxinput.py

@@ -85,3 +85,7 @@ class CheckboxInputTest(WidgetTest):
     def test_value_from_datadict_string_int(self):
         value = self.widget.value_from_datadict({'testing': '0'}, {}, 'testing')
         self.assertIs(value, True)
+
+    def test_value_omitted_from_data(self):
+        self.assertIs(self.widget.value_omitted_from_data({'field': 'value'}, {}, 'field'), False)
+        self.assertIs(self.widget.value_omitted_from_data({}, {}, 'field'), False)

tests/forms_tests/widget_tests/test_fileinput.py

@@ -14,3 +14,7 @@ class FileInputTest(WidgetTest):
         self.check_html(self.widget, 'email', 'test@example.com', html='<input type="file" name="email" />')
         self.check_html(self.widget, 'email', '', html='<input type="file" name="email" />')
         self.check_html(self.widget, 'email', None, html='<input type="file" name="email" />')
+
+    def test_value_omitted_from_data(self):
+        self.assertIs(self.widget.value_omitted_from_data({}, {}, 'field'), True)
+        self.assertIs(self.widget.value_omitted_from_data({}, {'field': 'value'}, 'field'), False)

tests/forms_tests/widget_tests/test_multiwidget.py

@@ -118,6 +118,13 @@ class MultiWidgetTest(WidgetTest):
             '<input id="bar_1" type="text" class="small" value="lennon" name="name_1" />'
         ))
 
+    def test_value_omitted_from_data(self):
+        widget = MyMultiWidget(widgets=(TextInput(), TextInput()))
+        self.assertIs(widget.value_omitted_from_data({}, {}, 'field'), True)
+        self.assertIs(widget.value_omitted_from_data({'field_0': 'x'}, {}, 'field'), False)
+        self.assertIs(widget.value_omitted_from_data({'field_1': 'y'}, {}, 'field'), False)
+        self.assertIs(widget.value_omitted_from_data({'field_0': 'x', 'field_1': 'y'}, {}, 'field'), False)
+
     def test_needs_multipart_true(self):
         """
         needs_multipart_form should be True if any widgets need it.

tests/forms_tests/widget_tests/test_selectdatewidget.py

@@ -477,3 +477,11 @@ class SelectDateWidgetTest(WidgetTest):
             w.value_from_datadict({'date_year': '1899', 'date_month': '8', 'date_day': '13'}, {}, 'date'),
             '13-08-1899',
         )
+
+    def test_value_omitted_from_data(self):
+        self.assertIs(self.widget.value_omitted_from_data({}, {}, 'field'), True)
+        self.assertIs(self.widget.value_omitted_from_data({'field_month': '12'}, {}, 'field'), False)
+        self.assertIs(self.widget.value_omitted_from_data({'field_year': '2000'}, {}, 'field'), False)
+        self.assertIs(self.widget.value_omitted_from_data({'field_day': '1'}, {}, 'field'), False)
+        data = {'field_day': '1', 'field_month': '12', 'field_year': '2000'}
+        self.assertIs(self.widget.value_omitted_from_data(data, {}, 'field'), False)

tests/forms_tests/widget_tests/test_widget.py

@@ -0,0 +1,12 @@
+from __future__ import unicode_literals
+
+from django.forms import Widget
+from django.test import SimpleTestCase
+
+
+class WidgetTests(SimpleTestCase):
+
+    def test_value_omitted_from_data(self):
+        widget = Widget()
+        self.assertIs(widget.value_omitted_from_data({}, {}, 'field'), True)
+        self.assertIs(widget.value_omitted_from_data({'field': 'value'}, {}, 'field'), False)

tests/model_forms/models.py

@@ -120,9 +120,11 @@ class PublicationDefaults(models.Model):
     CATEGORY_CHOICES = ((1, 'Games'), (2, 'Comics'), (3, 'Novel'))
     title = models.CharField(max_length=30)
     date_published = models.DateField(default=datetime.date.today)
+    datetime_published = models.DateTimeField(default=datetime.datetime(2000, 1, 1))
     mode = models.CharField(max_length=2, choices=MODE_CHOICES, default=default_mode)
     category = models.IntegerField(choices=CATEGORY_CHOICES, default=default_category)
     active = models.BooleanField(default=True)
+    file = models.FileField(default='default.txt')
 
 
 class Author(models.Model):

tests/model_forms/tests.py

@@ -601,6 +601,58 @@ class ModelFormBaseTest(TestCase):
         m1 = mf1.save(commit=False)
         self.assertEqual(m1.mode, mode)
 
+    def test_default_splitdatetime_field(self):
+        class PubForm(forms.ModelForm):
+            datetime_published = forms.SplitDateTimeField(required=False)
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ('datetime_published',)
+
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.datetime_published, datetime.datetime(2000, 1, 1))
+
+        mf2 = PubForm({'datetime_published_0': '2010-01-01', 'datetime_published_1': '0:00:00'})
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.datetime_published, datetime.datetime(2010, 1, 1))
+
+    def test_default_filefield(self):
+        class PubForm(forms.ModelForm):
+            class Meta:
+                model = PublicationDefaults
+                fields = ('file',)
+
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.file.name, 'default.txt')
+
+        mf2 = PubForm({}, {'file': SimpleUploadedFile('name', b'foo')})
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.file.name, 'name')
+
+    def test_selectdatewidget(self):
+        class PubForm(forms.ModelForm):
+            date_published = forms.DateField(required=False, widget=forms.SelectDateWidget)
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ('date_published',)
+
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.date_published, datetime.date.today())
+
+        mf2 = PubForm({'date_published_year': '2010', 'date_published_month': '1', 'date_published_day': '1'})
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.date_published, datetime.date(2010, 1, 1))
+
 
 class FieldOverridesByFormMetaForm(forms.ModelForm):
     class Meta:

tests/postgres_tests/models.py

@@ -40,7 +40,7 @@ class PostgreSQLModel(models.Model):
 
 
 class IntegerArrayModel(PostgreSQLModel):
-    field = ArrayField(models.IntegerField())
+    field = ArrayField(models.IntegerField(), default=[], blank=True)
 
 
 class NullableIntegerArrayModel(PostgreSQLModel):

tests/postgres_tests/test_array.py

@@ -20,7 +20,9 @@ from .models import (
 
 try:
     from django.contrib.postgres.fields import ArrayField
-    from django.contrib.postgres.forms import SimpleArrayField, SplitArrayField
+    from django.contrib.postgres.forms import (
+        SimpleArrayField, SplitArrayField, SplitArrayWidget,
+    )
 except ImportError:
     pass
 
@@ -714,3 +716,26 @@ class TestSplitFormField(PostgreSQLTestCase):
             'Item 0 in the array did not validate: Ensure this value has at most 2 characters (it has 3).',
             'Item 2 in the array did not validate: Ensure this value has at most 2 characters (it has 4).',
         ])
+
+    def test_splitarraywidget_value_omitted_from_data(self):
+        class Form(forms.ModelForm):
+            field = SplitArrayField(forms.IntegerField(), required=False, size=2)
+
+            class Meta:
+                model = IntegerArrayModel
+                fields = ('field',)
+
+        form = Form({'field_0': '1', 'field_1': '2'})
+        self.assertEqual(form.errors, {})
+        obj = form.save(commit=False)
+        self.assertEqual(obj.field, [1, 2])
+
+
+class TestSplitFormWidget(PostgreSQLTestCase):
+
+    def test_value_omitted_from_data(self):
+        widget = SplitArrayWidget(forms.TextInput(), size=2)
+        self.assertIs(widget.value_omitted_from_data({}, {}, 'field'), True)
+        self.assertIs(widget.value_omitted_from_data({'field_0': 'value'}, {}, 'field'), False)
+        self.assertIs(widget.value_omitted_from_data({'field_1': 'value'}, {}, 'field'), False)
+        self.assertIs(widget.value_omitted_from_data({'field_0': 'value', 'field_1': 'value'}, {}, 'field'), False)