Add Page methods can_move_to and can_create_at

These two tests are used when checking if a new page type can be created
under a page instance, or if an existing page type can move under a page
instance.

docs/reference/pages/model_reference.rst

@@ -119,14 +119,14 @@ In addition to the model fields provided, ``Page`` has many properties and metho
 
     .. attribute:: subpage_types
 
-        A whitelist of page models which can be created as children of this page type e.g a ``BlogIndex`` page might allow ``BlogPage``, but not ``JobPage`` e.g
+        A whitelist of page models which can be created as children of this page type. For example, a ``BlogIndex`` page might allow a ``BlogPage`` as a child, but not a ``JobPage``:
 
         .. code-block:: python
 
             class BlogIndex(Page):
                 subpage_types = ['mysite.BlogPage', 'mysite.BlogArchivePage']
 
-        The creation of child pages can be blocked altogether for a given page by setting it's subpage_types attribute to an empty array e.g
+        The creation of child pages can be blocked altogether for a given page by setting it's subpage_types attribute to an empty array:
 
         .. code-block:: python
 
@@ -135,20 +135,26 @@ In addition to the model fields provided, ``Page`` has many properties and metho
 
     .. attribute:: parent_page_types
 
-        A whitelist of page models which are allowed as parent page types e.g a ``BlogPage`` may only allow itself to be created below the ``BlogIndex`` page e.g
+        A whitelist of page models which are allowed as parent page types. For example, a ``BlogPage`` may only allow itself to be created below the ``BlogIndex`` page:
 
         .. code-block:: python
 
             class BlogPage(Page):
                 parent_page_types = ['mysite.BlogIndexPage']
 
-        Pages can block themselves from being created at all by setting parent_page_types to an empty array (this is useful for creating unique pages that should only be created once) e.g
+        Pages can block themselves from being created at all by setting parent_page_types to an empty array (this is useful for creating unique pages that should only be created once):
 
         .. code-block:: python
 
             class HiddenPage(Page):
                 parent_page_types = []
 
+    .. automethod:: can_exist_under
+
+    .. automethod:: can_create_at
+
+    .. automethod:: can_move_to
+
     .. attribute:: password_required_template
 
         Defines which template file should be used to render the login form for Protected pages using this model. This overrides the default, defined using ``PASSWORD_REQUIRED_TEMPLATE`` in your settings. See :ref:`private_pages`

wagtail/tests/testapp/migrations/0018_singletonpage.py

@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('wagtailcore', '0020_add_index_on_page_first_published_at'),
+        ('tests', '0017_businessnowherepage'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SingletonPage',
+            fields=[
+                ('page_ptr', models.OneToOneField(parent_link=True, auto_created=True, primary_key=True, serialize=False, to='wagtailcore.Page')),
+            ],
+            options={
+                'abstract': False,
+            },
+            bases=('wagtailcore.page',),
+        ),
+    ]

wagtail/tests/testapp/models.py

@@ -360,7 +360,7 @@ register_snippet(Advert)
 
 class StandardIndex(Page):
     """ Index for the site """
-    pass
+    parent_page_types = [Page]
 
 
 # A custom panel setup where all Promote fields are placed in the Content tab instead;
@@ -420,6 +420,12 @@ TaggedPage.content_panels = [
     FieldPanel('tags'),
 ]
 
+class SingletonPage(Page):
+    @classmethod
+    def can_create_at(cls, parent):
+        # You can only create one of these!
+        return super(SingletonPage, cls).can_create_at(parent) \
+            and not cls.objects.exists()
 
 class PageChooserModel(models.Model):
     page = models.ForeignKey('wagtailcore.Page', help_text='help text')

wagtail/wagtailadmin/views/pages.py

@@ -67,7 +67,8 @@ def add_subpage(request, parent_page_id):
 
     page_types = [
         (model.get_verbose_name(), model._meta.app_label, model._meta.model_name)
-        for model in parent_page.creatable_subpage_models()
+        for model in type(parent_page).creatable_subpage_models()
+        if model.can_create_at(parent_page)
     ]
     # sort by lower-cased version of verbose name
     page_types.sort(key=lambda page_type: page_type[0].lower())

wagtail/wagtailcore/models.py

@@ -750,6 +750,31 @@ class Page(six.with_metaclass(PageBase, MP_Node, ClusterableModel, index.Indexed
             if page_model.is_creatable
         ]
 
+    @classmethod
+    def can_exist_under(cls, parent):
+        """
+        Checks if this page type can exist as a subpage under a parent page
+        instance.
+
+        See also: :func:`Page.can_create_at` and :func:`Page.can_move_to`
+        """
+        return cls in parent.specific_class.allowed_subpage_models()
+
+    @classmethod
+    def can_create_at(cls, parent):
+        """
+        Checks if this page type can be created as a subpage under a parent
+        page instance.
+        """
+        return cls.is_creatable and cls.can_exist_under(parent)
+
+    def can_move_to(self, parent):
+        """
+        Checks if this page instance can be moved to be a subpage of a parent
+        page instance.
+        """
+        return self.can_exist_under(parent)
+
     @classmethod
     def get_verbose_name(cls):
         """
@@ -1388,7 +1413,7 @@ class PagePermissionTester(object):
     def can_add_subpage(self):
         if not self.user.is_active:
             return False
-        if not self.page.specific_class.allowed_subpage_models():  # this page model has an empty subpage_types list, so no subpages are allowed
+        if not self.page.specific_class.creatable_subpage_models():
             return False
         return self.user.is_superuser or ('add' in self.permissions)
 
@@ -1457,7 +1482,7 @@ class PagePermissionTester(object):
         """
         if not self.user.is_active:
             return False
-        if not self.page.specific_class.allowed_subpage_models():  # this page model has an empty subpage_types list, so no subpages are allowed
+        if not self.page.specific_class.creatable_subpage_models():
             return False
 
         return self.user.is_superuser or ('publish' in self.permissions)
@@ -1484,7 +1509,7 @@ class PagePermissionTester(object):
 
         # reject moves that are forbidden by subpage_types / parent_page_types rules
         # (these rules apply to superusers too)
-        if ContentType.objects.get_for_model(self.page.specific_class) not in destination.allowed_subpage_types():
+        if not self.page.specific.can_move_to(destination):
             return False
 
         # shortcut the trivial 'everything' / 'nothing' permissions

wagtail/wagtailcore/tests/test_page_model.py

@@ -16,10 +16,14 @@ from wagtail.tests.testapp.models import (
     BusinessIndex, BusinessSubIndex, BusinessChild, StandardIndex,
     MTIBasePage, MTIChildPage, AbstractPage, TaggedPage,
     BlogCategory, BlogCategoryBlogPage, Advert, ManyToManyBlogPage,
-    GenericSnippetPage, BusinessNowherePage)
+    GenericSnippetPage, BusinessNowherePage, SingletonPage)
 from wagtail.tests.utils import WagtailTestUtils
 
 
+def get_ct(model):
+    return ContentType.objects.get_for_model(model)
+
+
 class TestSiteRouting(TestCase):
     fixtures = ['test.json']
 
@@ -236,7 +240,6 @@ class TestServeView(TestCase):
         from django.core.urlresolvers import clear_url_caches
         clear_url_caches()
 
-
     def test_serve(self):
         response = self.client.get('/events/christmas/')
 
@@ -743,20 +746,20 @@ class TestSubpageTypeBusinessRules(TestCase, WagtailTestUtils):
         with self.ignore_deprecation_warnings():
             # SimplePage does not define any restrictions on subpage types
             # SimplePage is a valid subpage of SimplePage
-            self.assertIn(ContentType.objects.get_for_model(SimplePage), SimplePage.allowed_subpage_types())
+            self.assertIn(get_ct(SimplePage), SimplePage.allowed_subpage_types())
             # BusinessIndex is a valid subpage of SimplePage
-            self.assertIn(ContentType.objects.get_for_model(BusinessIndex), SimplePage.allowed_subpage_types())
+            self.assertIn(get_ct(BusinessIndex), SimplePage.allowed_subpage_types())
             # BusinessSubIndex is not valid, because it explicitly omits SimplePage from parent_page_types
-            self.assertNotIn(ContentType.objects.get_for_model(BusinessSubIndex), SimplePage.allowed_subpage_types())
+            self.assertNotIn(get_ct(BusinessSubIndex), SimplePage.allowed_subpage_types())
 
             # BusinessChild has an empty subpage_types list, so does not allow anything
-            self.assertNotIn(ContentType.objects.get_for_model(SimplePage), BusinessChild.allowed_subpage_types())
-            self.assertNotIn(ContentType.objects.get_for_model(BusinessIndex), BusinessChild.allowed_subpage_types())
-            self.assertNotIn(ContentType.objects.get_for_model(BusinessSubIndex), BusinessChild.allowed_subpage_types())
+            self.assertNotIn(get_ct(SimplePage), BusinessChild.allowed_subpage_types())
+            self.assertNotIn(get_ct(BusinessIndex), BusinessChild.allowed_subpage_types())
+            self.assertNotIn(get_ct(BusinessSubIndex), BusinessChild.allowed_subpage_types())
 
             # BusinessSubIndex only allows BusinessChild as subpage type
-            self.assertNotIn(ContentType.objects.get_for_model(SimplePage), BusinessSubIndex.allowed_subpage_types())
-            self.assertIn(ContentType.objects.get_for_model(BusinessChild), BusinessSubIndex.allowed_subpage_types())
+            self.assertNotIn(get_ct(SimplePage), BusinessSubIndex.allowed_subpage_types())
+            self.assertIn(get_ct(BusinessChild), BusinessSubIndex.allowed_subpage_types())
 
     def test_allowed_parent_page_models(self):
         # SimplePage does not define any restrictions on parent page types
@@ -783,17 +786,80 @@ class TestSubpageTypeBusinessRules(TestCase, WagtailTestUtils):
         with self.ignore_deprecation_warnings():
             # SimplePage does not define any restrictions on parent page types
             # SimplePage is a valid parent page of SimplePage
-            self.assertIn(ContentType.objects.get_for_model(SimplePage), SimplePage.allowed_parent_page_types())
+            self.assertIn(get_ct(SimplePage), SimplePage.allowed_parent_page_types())
             # BusinessChild cannot be a parent of anything
-            self.assertNotIn(ContentType.objects.get_for_model(BusinessChild), SimplePage.allowed_parent_page_types())
+            self.assertNotIn(get_ct(BusinessChild), SimplePage.allowed_parent_page_types())
 
             # BusinessNowherePage does not allow anything as a parent
-            self.assertNotIn(ContentType.objects.get_for_model(SimplePage), BusinessNowherePage.allowed_parent_page_types())
-            self.assertNotIn(ContentType.objects.get_for_model(StandardIndex), BusinessNowherePage.allowed_parent_page_types())
+            self.assertNotIn(get_ct(SimplePage), BusinessNowherePage.allowed_parent_page_types())
+            self.assertNotIn(get_ct(StandardIndex), BusinessNowherePage.allowed_parent_page_types())
 
             # BusinessSubIndex only allows BusinessIndex as a parent
-            self.assertNotIn(ContentType.objects.get_for_model(SimplePage), BusinessSubIndex.allowed_parent_page_types())
-            self.assertIn(ContentType.objects.get_for_model(BusinessIndex), BusinessSubIndex.allowed_parent_page_types())
+            self.assertNotIn(get_ct(SimplePage), BusinessSubIndex.allowed_parent_page_types())
+            self.assertIn(get_ct(BusinessIndex), BusinessSubIndex.allowed_parent_page_types())
+
+    def test_can_exist_under(self):
+        self.assertTrue(SimplePage.can_exist_under(SimplePage()))
+
+        # StandardIndex should only be allowed under a Page
+        self.assertTrue(StandardIndex.can_exist_under(Page()))
+        self.assertFalse(StandardIndex.can_exist_under(SimplePage()))
+
+        # The Business pages are quite restrictive in their structure
+        self.assertTrue(BusinessSubIndex.can_exist_under(BusinessIndex()))
+        self.assertTrue(BusinessChild.can_exist_under(BusinessIndex()))
+        self.assertTrue(BusinessChild.can_exist_under(BusinessSubIndex()))
+
+        self.assertFalse(BusinessSubIndex.can_exist_under(SimplePage()))
+        self.assertFalse(BusinessSubIndex.can_exist_under(BusinessSubIndex()))
+        self.assertFalse(BusinessChild.can_exist_under(SimplePage()))
+
+    def test_can_create_at(self):
+        # Pages are not `is_creatable`, and should not be creatable
+        self.assertFalse(Page.can_create_at(Page()))
+
+        # SimplePage can be created under a simple page
+        self.assertTrue(SimplePage.can_create_at(SimplePage()))
+
+        # StandardIndex can be created under a Page, but not a SimplePage
+        self.assertTrue(StandardIndex.can_create_at(Page()))
+        self.assertFalse(StandardIndex.can_create_at(SimplePage()))
+
+        # The Business pages are quite restrictive in their structure
+        self.assertTrue(BusinessSubIndex.can_create_at(BusinessIndex()))
+        self.assertTrue(BusinessChild.can_create_at(BusinessIndex()))
+        self.assertTrue(BusinessChild.can_create_at(BusinessSubIndex()))
+
+        self.assertFalse(BusinessChild.can_create_at(SimplePage()))
+        self.assertFalse(BusinessSubIndex.can_create_at(SimplePage()))
+
+    def test_can_move_to(self):
+        self.assertTrue(SimplePage().can_move_to(SimplePage()))
+
+        # StandardIndex should only be allowed under a Page
+        self.assertTrue(StandardIndex().can_move_to(Page()))
+        self.assertFalse(StandardIndex().can_move_to(SimplePage()))
+
+        # The Business pages are quite restrictive in their structure
+        self.assertTrue(BusinessSubIndex().can_move_to(BusinessIndex()))
+        self.assertTrue(BusinessChild().can_move_to(BusinessIndex()))
+        self.assertTrue(BusinessChild().can_move_to(BusinessSubIndex()))
+
+        self.assertFalse(BusinessChild().can_move_to(SimplePage()))
+        self.assertFalse(BusinessSubIndex().can_move_to(SimplePage()))
+
+    def test_singleton_page_creation(self):
+        root_page = Page.objects.get(url_path='/home/')
+
+        # A single singleton page should be creatable
+        self.assertTrue(SingletonPage.can_create_at(root_page))
+
+        # Create a singleton page
+        root_page.add_child(instance=SingletonPage(
+            title='singleton', slug='singleton'))
+
+        # A second singleton page should not be creatable
+        self.assertFalse(SingletonPage.can_create_at(root_page))
 
 
 class TestIssue735(TestCase):

wagtail/wagtailcore/tests/test_page_permissions.py

@@ -141,8 +141,8 @@ class TestPagePermission(TestCase):
 
     def test_superuser_has_full_permissions(self):
         user = get_user_model().objects.get(username='superuser')
-        homepage = Page.objects.get(url_path='/home/')
-        root = Page.objects.get(url_path='/')
+        homepage = Page.objects.get(url_path='/home/').specific
+        root = Page.objects.get(url_path='/').specific
         unpublished_event_page = EventPage.objects.get(url_path='/home/events/tentative-unpublished-event/')
         board_meetings_page = BusinessSubIndex.objects.get(url_path='/home/events/businessy-events/board-meetings/')