Related polymorphic query support inc select_related and prefetch_related

docs/advanced.rst

@@ -193,9 +193,34 @@ About Queryset Methods
 *   :meth:`~django.db.models.query.QuerySet.distinct` works as expected. It only regards the fields
     of the base class, but this should never make a difference.
 
-*   :meth:`~django.db.models.query.QuerySet.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')`` )
+*   :meth:`~django.db.models.query.QuerySet.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')``
 
 *   :meth:`~django.db.models.query.QuerySet.extra` works as expected (it returns polymorphic
     results) but currently has one restriction: The resulting objects are required to have a unique