Related polymorphic query support inc select_related and prefetch_related

docs/advanced.rst

@@ -167,9 +167,34 @@ About Queryset Methods
 *   ``distinct()`` works as expected. It only regards the fields of
     the base class, but this should never make a difference.
 
-*   ``select_related()`` works just as usual, but it can not (yet) be used
-    to select relations in inherited models
-    (like ``ModelA.objects.select_related('ModelC___fieldxy')`` )
+*   ``select_related()`` works just as usual with the exception that the
+    query set must be derived from a PolymorphicRelatedQuerySetMixin
+    or PolymorphicRelatedQuerySet.
+
+    This can be achieved by using a custom manager
+
+        class NonPolyModel(models.Model):
+            relation = models.ForeignKey(BasePolyModel, on_delete=models.CASCADE)
+            objects = models.Manager.from_queryset(PolymorphicRelatedQuerySet)()
+
+    or by converting a models queryset using
+
+        class NonPolyModel(models.Model):
+            relation = models.ForeignKey(BasePolyModel, on_delete=models.CASCADE)
+            objects = models.Manager.from_queryset(QuerySet)()
+
+    ``convert_to_polymorphic_queryset(NonPolyModel.objects).filter(...)``
+
+    To select related fields the model name comes after the field name and set the
+    field.
+    ``ModelA.objects.filter(....).select_related('field___TargetModel__subfield')``.
+    or using the polymorphic added related fieldname which is normally the lowercase
+    version of the model name.
+    ``ModelA.objects.filter(....).select_related('field__targetmodel__subfield')``
+
+    This automatically manages the via models between the model specified in the related
+    field and the target model.
+    ``ModelA.objects.filter(....).select_related('field__targetparentmodel__targetmodel__subfield')``
 
 *   ``extra()`` works as expected (it returns polymorphic results) but
     currently has one restriction: The resulting objects are required to have

polymorphic/base.py

@@ -73,7 +73,7 @@ def __new__(self, model_name, bases, attrs, **kwargs):
         # determine the name of the primary key field and store it into the class variable
         # polymorphic_primary_key_name (it is needed by query.py)
         for f in new_class._meta.fields:
-            if f.primary_key and type(f) != models.OneToOneField:
+            if f.primary_key and not isinstance(f, models.OneToOneField):
                 new_class.polymorphic_primary_key_name = f.name
                 break
 

polymorphic/formsets/utils.py

@@ -3,6 +3,7 @@
 """
 
 
+
 def add_media(dest, media):
     """
     Optimized version of django.forms.Media.__add__() that doesn't create new objects.

polymorphic/models.py

@@ -192,11 +192,15 @@ def __init__(self, *args, **kwargs):
             return
         self.__class__.polymorphic_super_sub_accessors_replaced = True
 
-        def create_accessor_function_for_model(model, accessor_name):
+        def create_accessor_function_for_model(model, field):
             def accessor_function(self):
-                objects = getattr(model, "_base_objects", model.objects)
-                attr = objects.get(pk=self.pk)
-                return attr
+                try:
+                    rel_obj = field.get_cached_value(self)
+                except KeyError:
+                    objects = getattr(model, "_base_objects", model.objects)
+                    rel_obj = objects.get(pk=self.pk)
+                    field.set_cached_value(self, rel_obj)
+                return rel_obj
 
             return accessor_function
 
@@ -209,10 +213,14 @@ def accessor_function(self):
                 type(orig_accessor),
                 (ReverseOneToOneDescriptor, ForwardManyToOneDescriptor),
             ):
+
+                field = orig_accessor.related \
+                    if isinstance(orig_accessor, ReverseOneToOneDescriptor) else orig_accessor.field
+
                 setattr(
                     self.__class__,
                     name,
-                    property(create_accessor_function_for_model(model, name)),
+                    property(create_accessor_function_for_model(model, field)),
                 )
 
     def _get_inheritance_relation_fields_and_models(self):