[pull] main from django:main

django/db/models/base.py

@@ -28,7 +28,14 @@
     router,
     transaction,
 )
-from django.db.models import NOT_PROVIDED, ExpressionWrapper, IntegerField, Max, Value
+from django.db.models import (
+    NOT_PROVIDED,
+    Expression,
+    ExpressionWrapper,
+    IntegerField,
+    Max,
+    Value,
+)
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.deletion import CASCADE, DO_NOTHING, Collector, DatabaseOnDelete
 from django.db.models.expressions import DatabaseDefault
@@ -1295,7 +1302,9 @@ def _prepare_related_fields_for_save(self, operation_name, fields=None):
                         "%s() prohibited to prevent data loss due to unsaved "
                         "related object '%s'." % (operation_name, field.name)
                     )
-                elif getattr(self, field.attname) in field.empty_values:
+                if (
+                    field_val := getattr(self, field.attname)
+                ) in field.empty_values or isinstance(field_val, Expression):
                     # Set related object if it has been saved after an
                     # assignment.
                     setattr(self, field.name, obj)

tests/field_defaults/models.py

@@ -13,7 +13,7 @@
 from decimal import Decimal
 
 from django.db import models
-from django.db.models.functions import Coalesce, ExtractYear, Now, Pi
+from django.db.models.functions import UUID4, Coalesce, ExtractYear, Now, Pi
 from django.db.models.lookups import GreaterThan
 
 
@@ -78,3 +78,23 @@ class DBDefaultsOneToOnePK(models.Model):
         db_default="kr",
         on_delete=models.CASCADE,
     )
+
+
+class DBDefaultsFunctionPK(models.Model):
+    uuid = models.UUIDField(primary_key=True, db_default=UUID4())
+
+    class Meta:
+        required_db_features = {
+            "supports_uuid4_function_in_default",
+            "supports_expression_defaults",
+        }
+
+
+class DBDefaultsFunctionFK(models.Model):
+    parent = models.ForeignKey(DBDefaultsFunctionPK, models.CASCADE)
+
+    class Meta:
+        required_db_features = {
+            "supports_uuid4_function_in_default",
+            "supports_expression_defaults",
+        }

tests/field_defaults/tests.py

@@ -13,7 +13,7 @@
     OrderByList,
     RawSQL,
 )
-from django.db.models.functions import Collate
+from django.db.models.functions import UUID4, Collate
 from django.db.models.lookups import GreaterThan
 from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
 
@@ -23,6 +23,8 @@
     DBDefaults,
     DBDefaultsFK,
     DBDefaultsFunction,
+    DBDefaultsFunctionFK,
+    DBDefaultsFunctionPK,
     DBDefaultsOneToOnePK,
     DBDefaultsPK,
 )
@@ -155,6 +157,18 @@ def test_primary_key_assigned_db_default_expression(self):
         # DatabaseDefault is used, but this behavior varies across databases.
         self.assertNotEqual(obj.language_code_id, "tr")
 
+    @skipUnlessDBFeature(
+        "can_return_columns_from_insert",
+        "supports_expression_defaults",
+        "supports_uuid4_function_in_default",
+    )
+    def test_foreign_key_to_parent_with_expression_pk(self):
+        parent = DBDefaultsFunctionPK(pk=UUID4())
+        obj = DBDefaultsFunctionFK(parent=parent)
+        parent.save()
+        obj.save()
+        self.assertEqual(obj.parent_id, parent.pk)
+
     @skipUnlessDBFeature("supports_expression_defaults")
     def test_case_when_db_default_returning(self):
         m = DBDefaultsFunction.objects.create()