Fixed #23617 -- Added get_pk_value_on_save()

The method is mainly intended for use with UUIDField. For UUIDField we
want to call the field's default even when primary key value is
explicitly set to None to match the behavior of AutoField.

Thanks to Marc Tamlyn and Tim Graham for review.

2 files changed, 12 insertions, 0 deletions

diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index 01fcb1a4ed..4eb16d4345 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -217,6 +217,15 @@ Note that ``lambda``\s cannot be used for field options like ``default``
 because they cannot be :ref:`serialized by migrations <migration-serializing>`.
 See that documentation for other caveats.
 
+The default value is used when new model instances are created and a value
+isn't provided for the field. When the field is a primary key, the default is
+also used when the field is set to ``None``.
+
+.. versionchanged:: 1.8
+
+    The default wasn't used for ``None`` primary key values in previous
+    versions.
+
 ``editable``
 ------------
 
diff --git a/docs/releases/1.8.txt b/docs/releases/1.8.txt
index bee112b713..bbb932ada3 100644
--- a/docs/releases/1.8.txt
+++ b/docs/releases/1.8.txt
@@ -526,6 +526,9 @@ Models
 * You can now get the set of deferred fields for a model using
   :meth:`Model.get_deferred_fields() <django.db.models.Model.get_deferred_fields>`.
 
+* Model field ``default``’s are now used when primary key field's are set to
+  ``None``.
+
 Signals
 ^^^^^^^