Add a dont_use_model_field_default_for_empty_data flag to BlockWidget to stop Django 1.10.1 from skipping it

Fixes #2994 for Django 1.10.1 ONLY.

wagtail/tests/testapp/migrations/0009_defaultstreampage.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.1 on 2016-09-21 11:37
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+import wagtail.wagtailcore.blocks
+import wagtail.wagtailcore.fields
+import wagtail.wagtailimages.blocks
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('wagtailcore', '0030_index_on_pagerevision_created_at'),
+        ('tests', '0008_inlinestreampage_inlinestreampagesection'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='DefaultStreamPage',
+            fields=[
+                ('page_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='wagtailcore.Page')),
+                ('body', wagtail.wagtailcore.fields.StreamField((('text', wagtail.wagtailcore.blocks.CharBlock()), ('rich_text', wagtail.wagtailcore.blocks.RichTextBlock()), ('image', wagtail.wagtailimages.blocks.ImageChooserBlock())), default='')),
+            ],
+            options={
+                'abstract': False,
+            },
+            bases=('wagtailcore.page',),
+        ),
+    ]

wagtail/tests/testapp/models.py

@@ -556,6 +556,19 @@ class StreamPage(Page):
     ]
 
 
+class DefaultStreamPage(Page):
+    body = StreamField([
+        ('text', CharBlock()),
+        ('rich_text', RichTextBlock()),
+        ('image', ImageChooserBlock()),
+    ], default='')
+
+    content_panels = [
+        FieldPanel('title'),
+        StreamFieldPanel('body'),
+    ]
+
+
 class MTIBasePage(Page):
     is_creatable = False
 

wagtail/wagtailadmin/tests/test_pages_views.py

@@ -21,6 +21,7 @@ from django.utils.dateparse import parse_date
 
 from wagtail.tests.testapp.models import (
     EVENT_AUDIENCE_CHOICES, Advert, AdvertPlacement, BusinessChild, BusinessIndex, BusinessSubIndex,
+    DefaultStreamPage,
     EventPage, EventPageCarouselItem, FilePage, SimplePage, SingleEventPage, SingletonPage,
     StandardChild, StandardIndex, TaggedPage)
 from wagtail.tests.utils import WagtailTestUtils
@@ -3511,3 +3512,36 @@ class TestRecentEditsPanel(TestCase, WagtailTestUtils):
         # Alice's dashboard should still list that first edit
         response = self.go_to_dashboard_response()
         self.assertIn('Your most recent edits', response.content.decode('utf-8'))
+
+
+class TestIssue2994(TestCase, WagtailTestUtils):
+    """
+    When submitting the add/edit page form, Django 1.10.1 fails to update StreamFields
+    that have a default value, because it notices the lack of postdata field
+    with a name exactly matching the field name and wrongly assumes that the field has
+    been omitted from the form. To avoid this in Django 1.10.1, we need to set
+    dont_use_model_field_default_for_empty_data=True on the widget; in Django >=1.10.2,
+    we need to provide a custom value_omitted_from_data method.
+    """
+    def setUp(self):
+        self.root_page = Page.objects.get(id=2)
+        self.user = self.login()
+
+    def test_page_edit_post_publish_url(self):
+        # Post
+        post_data = {
+            'title': "Issue 2994 test",
+            'slug': 'issue-2994-test',
+            'body-count': '1',
+            'body-0-deleted': '',
+            'body-0-order': '0',
+            'body-0-type': 'text',
+            'body-0-value': 'hello world',
+            'action-publish': "Publish",
+        }
+        self.client.post(
+            reverse('wagtailadmin_pages:add', args=('tests', 'defaultstreampage', self.root_page.id)), post_data
+        )
+        new_page = DefaultStreamPage.objects.get(slug='issue-2994-test')
+        self.assertEqual(1, len(new_page.body))
+        self.assertEqual('hello world', new_page.body[0].value)

wagtail/wagtailcore/blocks/base.py

@@ -559,6 +559,12 @@ class DeclarativeSubBlocksMetaclass(BaseBlock):
 
 class BlockWidget(forms.Widget):
     """Wraps a block object as a widget so that it can be incorporated into a Django form"""
+
+    # Flag used by Django 1.10.1 (only) to indicate that this widget will not necessarily submit
+    # a postdata item with a name that matches the field name -
+    # see https://github.com/django/django/pull/7068, https://github.com/torchbox/wagtail/issues/2994
+    dont_use_model_field_default_for_empty_data = True
+
     def __init__(self, block_def, attrs=None):
         super(BlockWidget, self).__init__(attrs=attrs)
         self.block_def = block_def