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

django/db/models/base.py

@@ -15,6 +15,7 @@ from django.db import (
     DEFAULT_DB_ALIAS, DJANGO_VERSION_PICKLE_KEY, DatabaseError, connection,
     connections, router, transaction,
 )
+from django.db.models import NOT_PROVIDED
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.constraints import CheckConstraint, UniqueConstraint
 from django.db.models.deletion import CASCADE, Collector
@@ -842,6 +843,14 @@ class Model(metaclass=ModelBase):
         if not pk_set and (force_update or update_fields):
             raise ValueError("Cannot force an update in save() with no primary key.")
         updated = False
+        # Skip an UPDATE when adding an instance and primary key has a default.
+        if (
+            not force_insert and
+            self._state.adding and
+            self._meta.pk.default and
+            self._meta.pk.default is not NOT_PROVIDED
+        ):
+            force_insert = True
         # If possible, try an UPDATE. If that doesn't update anything, do an INSERT.
         if pk_set and not force_insert:
             base_qs = cls._base_manager.using(using)