Use get_base_queryset in related pages fields

Eg, children, descendants and parent

This fixes a very minor bug in the admin API where the "parent" field
wasn't being populated if it that page was outside of the default site.

wagtail/admin/api/serializers.py

@@ -51,7 +51,7 @@ class PageChildrenField(Field):
 
     def to_representation(self, page):
         return OrderedDict([
-            ('count', page.numchild),
+            ('count', self.context['base_queryset'].child_of(page).count()),
             ('listing_url', get_model_listing_url(self.context, Page) + '?child_of=' + str(page.id)),
         ])
 
@@ -71,7 +71,7 @@ class PageDescendantsField(Field):
 
     def to_representation(self, page):
         return OrderedDict([
-            ('count', page.get_descendants().count()),
+            ('count', self.context['base_queryset'].descendant_of(page).count()),
             ('listing_url', get_model_listing_url(self.context, Page) + '?descendant_of=' + str(page.id)),
         ])
 

wagtail/admin/tests/api/test_pages.py

@@ -518,6 +518,14 @@ class TestAdminPageDetail(AdminAPITestCase, TestPageDetail):
         self.assertEqual(content['__types']['demosite.BlogIndexPage']['verbose_name'], 'blog index page')
         self.assertEqual(content['__types']['demosite.BlogIndexPage']['verbose_name_plural'], 'blog index pages')
 
+    # Overriden from public API tests
+    def test_meta_parent_id_doesnt_show_root_page(self):
+        # Root page is visible in the admin API
+        response = self.get_response(2)
+        content = json.loads(response.content.decode('UTF-8'))
+
+        self.assertIsNotNone(content['meta']['parent'])
+
     def test_field_ordering(self):
         # Need to override this as the admin API has a __types field
 

wagtail/api/v2/endpoints.py

@@ -464,3 +464,11 @@ class PagesAPIViewSet(BaseAPIViewSet):
                 return page
 
         return super().find_object(queryset, request)
+
+    def get_serializer_context(self):
+        """
+        The serialization context differs between listing and detail views.
+        """
+        context = super().get_serializer_context()
+        context['base_queryset'] = self.get_base_queryset()
+        return context

wagtail/api/v2/serializers.py

@@ -8,7 +8,7 @@ from taggit.managers import _TaggableManager
 
 from wagtail.core import fields as wagtailcore_fields
 
-from .utils import get_object_detail_url, pages_for_site
+from .utils import get_object_detail_url
 
 
 class TypeField(Field):
@@ -121,8 +121,7 @@ class PageParentField(relations.RelatedField):
     def get_attribute(self, instance):
         parent = instance.get_parent()
 
-        site_pages = pages_for_site(self.context['request'].site)
-        if site_pages.filter(id=parent.id).exists():
+        if self.context['base_queryset'].filter(id=parent.id).exists():
             return parent
 
     def to_representation(self, value):

wagtail/api/v2/utils.py

@@ -32,12 +32,6 @@ def get_object_detail_url(router, request, model, pk):
         return get_full_url(request, url_path)
 
 
-def pages_for_site(site):
-    pages = Page.objects.public().live()
-    pages = pages.descendant_of(site.root_page, inclusive=True)
-    return pages
-
-
 def page_models_from_string(string):
     page_models = []