From 9225f0814118c17af857c85a7cc5319bbb48ee43 Mon Sep 17 00:00:00 2001
From: Michael Scott Cuthbert <cuthbert@mit.edu>
Date: Mon, 29 Jan 2018 20:04:41 -0500
Subject: [PATCH] Give an example of copying a polymorphic object

---
 docs/advanced.rst | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/docs/advanced.rst b/docs/advanced.rst
index bcffe50..a091c8e 100644
--- a/docs/advanced.rst
+++ b/docs/advanced.rst
@@ -92,6 +92,20 @@ A ManyToManyField example::
       <ModelB: id 2, field1 (CharField), field2 (CharField)>,
       <ModelC: id 3, field1 (CharField), field2 (CharField), field3 (CharField)> ]
 
+Copying Polymorphic objects
+---------------------------
+
+When creating a copy of a polymorphic object, both the
+``.id`` and the ``.pk`` of the object need to be set
+to ``None`` before saving so that both the base table
+and the derived table will be updated to the new object::
+
+    >>> o = ModelB.objects.first()
+    >>> o.field1 = 'new val' # leave field2 unchanged
+    >>> o.pk = None
+    >>> o.id = None
+    >>> o.save()
+
 
 Using Third Party Models (without modifying them)
 -------------------------------------------------