[1.10.x] Documented how to copy a OneToOneField.

Thanks Anton Gilgur for the report and review.

Backport of 2f44fa7f069427e2da18a0f6cb2ffc29699f2ca3 from master

1 files changed, 9 insertions, 0 deletions

diff --git a/docs/topics/db/queries.txt b/docs/topics/db/queries.txt
index afa1f6be43..a32a3b33d6 100644
--- a/docs/topics/db/queries.txt
+++ b/docs/topics/db/queries.txt
@@ -993,6 +993,15 @@ entry::
     entry.save()
     entry.authors.set(old_authors)
 
+For a ``OneToOneField``, you must duplicate the related object and assign it
+to the new object's field to avoid violating the one-to-one unique constraint.
+For example, assuming ``entry`` is already duplicated as above::
+
+    detail = EntryDetail.objects.all()[0]
+    detail.pk = None
+    detail.entry = entry
+    detail.save()
+
 .. _topics-db-queries-update:
 
 Updating multiple objects at once