Fixed #29260 -- Skipped an UPDATE when adding a model instance with primary key that has a default.

tests/basic/models.py

@@ -3,6 +3,8 @@ Bare-bones model
 
 This is a basic model with only two non-primary-key fields.
 """
+import uuid
+
 from django.db import models
 
 
@@ -40,3 +42,7 @@ class SelfRef(models.Model):
         # This method intentionally doesn't work for all cases - part
         # of the test for ticket #20278
         return SelfRef.objects.get(selfref=self).pk
+
+
+class PrimaryKeyWithDefault(models.Model):
+    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4)