Improve ICEKit Publishing support for Polymorphic models

- add supporting class helpers for working with plain polymorphic models
  that are not also `UrlNode`s or `FluentContentsPage`s:
  `PublishingPolymorphicQuerySet`, `PublishingPolymorphicManager`
- fix some assumptions about model admins that don't hold for
  polymorphic parent and basic admins, such as `change_form_template`
  isn't always available
- don't perform placeholder cloning or patching for models that are
  not `FluentContentsPage`s

Author: jmurty

icekit/publishing/admin.py

@@ -297,8 +297,11 @@ def __init__(self, model, admin_site):
             self.admin_site.name,
             self.get_url_name_prefix(model), )
 
-        self.non_publishing_change_form_template = \
-            self.find_first_available_template(self.change_form_template)
+        # Some admins are missing a `change_form_template` such as
+        # PolymorphicParentModelAdmin
+        if self.change_form_template:
+            self.non_publishing_change_form_template = \
+                self.find_first_available_template(self.change_form_template)
 
     def find_first_available_template(self, template_name_list):
         """
@@ -518,13 +521,13 @@ def render_change_form(self, request, context, add=False, change=False,
         # Override this admin's change form template to point to the publishing
         # admin page template, but only for long enough to render the change
         # form.
-        if isinstance(self, DefaultPageChildAdmin) \
+        if hasattr(type(self).change_form_template, '__get__') \
                 and isinstance(self.change_form_template, (list, tuple)):
-            # Special handling for `DefaultPageChildAdmin` subclases with
-            # multiple templates, a feature of FluentPages that is as confusing
-            # as it is helpful. In this case, find the best available template
-            # preferring publishing-specific templates and apply it via
-            # a context variable that should be respected by Fluent's base
+            # Special handling for class that provide multiple templates via,
+            # a `change_form_template` get-only property instead of the usual
+            # plain class attribute.  In this case, find the best available
+            # template preferring publishing-specific templates and apply it
+            # via a context variable that should be respected by Fluent's base
             # templates, which we are most likely using at this point.
             opts = self.model._meta
             app_label = opts.app_label

icekit/publishing/apps.py

@@ -6,12 +6,14 @@
 from fluent_pages.models import UrlNode
 from fluent_pages.models.managers import UrlNodeQuerySet
 
+from polymorphic.polymorphic_model import PolymorphicModel
+
 from mptt.models import MPTTModel
 
 from . import monkey_patches
-from .managers import PublishingQuerySet, PublishingUrlNodeManager, \
-    UrlNodeQuerySetWithPublishingFeatures, DraftItemBoobyTrap, \
-    _queryset_iterator
+from .managers import PublishingQuerySet, PublishingPolymorphicManager, \
+    PublishingUrlNodeManager, UrlNodeQuerySetWithPublishingFeatures, \
+    DraftItemBoobyTrap, _queryset_iterator
 from .models import PublishingModel
 from .middleware import is_draft_request_context, \
     is_publishing_middleware_active
@@ -217,6 +219,13 @@ def _filter_candidates_by_published_status(candidates, model, path):
             if not issubclass(model, PublishingModel):
                 continue
 
+            if issubclass(model, PolymorphicModel):
+
+                PublishingPolymorphicManager().contribute_to_class(
+                    model, 'objects')
+                PublishingPolymorphicManager().contribute_to_class(
+                    model, '_default_manager')
+
             if issubclass(model, UrlNode):
 
                 PublishingUrlNodeManager().contribute_to_class(

icekit/publishing/managers.py

@@ -3,6 +3,9 @@
 from django.db.models.query_utils import Q
 from django.utils.timezone import now
 
+from polymorphic.manager import PolymorphicManager
+from polymorphic.query import PolymorphicQuerySet
+
 from fluent_pages.models.managers import UrlNodeQuerySet, UrlNodeManager
 from fluent_pages.models.db import UrlNode
 
@@ -318,6 +321,10 @@ def only(self, *args, **kwargs):
             .only(*field_names, **kwargs)
 
 
+class PublishingPolymorphicQuerySet(PublishingQuerySet, PolymorphicQuerySet):
+    pass
+
+
 class PublishingUrlNodeQuerySet(PublishingQuerySet, UrlNodeQuerySet):
     """
     Publishing queryset with customisations for UrlNode support.
@@ -407,6 +414,15 @@ def get_queryset(self):
         return PublishingQuerySet(self.model, using=self._db).all()
 
 
+class PublishingPolymorphicManager(PolymorphicManager, PublishingManager):
+    """
+    Publishing manager with polymorphic support and customisations.
+    """
+    queryset_class = PublishingPolymorphicQuerySet
+    # Tell Django that related fields also need to use this manager:
+    use_for_related_fields = True
+
+
 class PublishingUrlNodeManager(UrlNodeManager, PublishingManager):
     """
     Publishing manager with UrlNode support and customisations.

icekit/publishing/models.py

@@ -446,6 +446,8 @@ def clone(src, dst):
 
     @assert_draft
     def patch_placeholders(self):
+        if not isinstance(self, FluentContentsPage):
+            return
         published_obj = self.publishing_linked
 
         for draft_placeholder, published_placeholder in zip(
@@ -492,6 +494,8 @@ def clone_placeholder(self, dst_obj):
         are to be related.
         :return: None
         """
+        if not isinstance(self, FluentContentsPage):
+            return
         for src_placeholder in Placeholder.objects.parent(self):
             dst_placeholder = Placeholder.objects.create_for_object(
                 dst_obj,