Refs #27222 -- Refreshed GeneratedFields values on save() initiated update.

This required implementing UPDATE RETURNING machinery that heavily
borrows from the INSERT one.

tests/model_fields/test_generatedfield.py

@@ -173,11 +173,6 @@ class BaseGeneratedFieldTests(SimpleTestCase):
 
 
 class GeneratedFieldTestMixin:
-    def _refresh_if_needed(self, m):
-        if not connection.features.can_return_columns_from_insert:
-            m.refresh_from_db()
-        return m
-
     def test_unsaved_error(self):
         m = self.base_model(a=1, b=2)
         msg = "Cannot retrieve deferred field 'field' from an unsaved model."
@@ -189,8 +184,11 @@ class GeneratedFieldTestMixin:
         # full_clean() ignores GeneratedFields.
         m.full_clean()
         m.save()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.field, 3)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 3)
 
     @skipUnlessDBFeature("supports_table_check_constraints")
     def test_full_clean_with_check_constraint(self):
@@ -199,8 +197,11 @@ class GeneratedFieldTestMixin:
         m = self.check_constraint_model(a=2)
         m.full_clean()
         m.save()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.a_squared, 4)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.a_squared, 4)
 
         m = self.check_constraint_model(a=-1)
         with self.assertRaises(ValidationError) as cm:
@@ -217,8 +218,11 @@ class GeneratedFieldTestMixin:
         m = self.unique_constraint_model(a=2)
         m.full_clean()
         m.save()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.a_squared, 4)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.a_squared, 4)
 
         m = self.unique_constraint_model(a=2)
         with self.assertRaises(ValidationError) as cm:
@@ -230,8 +234,11 @@ class GeneratedFieldTestMixin:
 
     def test_create(self):
         m = self.base_model.objects.create(a=1, b=2)
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.field, 3)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 3)
 
     def test_non_nullable_create(self):
         with self.assertRaises(IntegrityError):
@@ -241,26 +248,52 @@ class GeneratedFieldTestMixin:
         # Insert.
         m = self.base_model(a=2, b=4)
         m.save()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.field, 6)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 6)
         # Update.
         m.a = 4
         m.save()
-        m.refresh_from_db()
-        self.assertEqual(m.field, 8)
+        expected_num_queries = (
+            0 if connection.features.can_return_rows_from_update else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 8)
+        # Update non-dependent field.
+        self.base_model.objects.filter(pk=m.pk).update(a=6)
+        m.save(update_fields=["fk"])
+        with self.assertNumQueries(0):
+            self.assertEqual(m.field, 8)
+        # Update dependent field without persisting local changes.
+        m.save(update_fields=["b"])
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 10)
+        # Update dependent field while persisting local changes.
+        m.a = 8
+        m.save(update_fields=["a"])
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 12)
 
     def test_save_model_with_pk(self):
         m = self.base_model(pk=1, a=1, b=2)
         m.save()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.field, 3)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 3)
 
     def test_save_model_with_foreign_key(self):
         fk_object = Foo.objects.create(a="abc", d=Decimal("12.34"))
         m = self.base_model(a=1, b=2, fk=fk_object)
         m.save()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.field, 3)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, 3)
 
     def test_generated_fields_can_be_deferred(self):
         fk_object = Foo.objects.create(a="abc", d=Decimal("12.34"))
@@ -330,17 +363,23 @@ class GeneratedFieldTestMixin:
 
     def test_model_with_params(self):
         m = self.params_model.objects.create()
-        m = self._refresh_if_needed(m)
-        self.assertEqual(m.field, "Constant")
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m.field, "Constant")
 
     def test_nullable(self):
         m1 = self.nullable_model.objects.create()
-        m1 = self._refresh_if_needed(m1)
         none_val = "" if connection.features.interprets_empty_strings_as_nulls else None
-        self.assertEqual(m1.lower_name, none_val)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m1.lower_name, none_val)
         m2 = self.nullable_model.objects.create(name="NaMe")
-        m2 = self._refresh_if_needed(m2)
-        self.assertEqual(m2.lower_name, "name")
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(m2.lower_name, "name")
 
 
 @skipUnlessDBFeature("supports_stored_generated_columns")
@@ -354,8 +393,21 @@ class StoredGeneratedFieldTests(GeneratedFieldTestMixin, TestCase):
 
     def test_create_field_with_db_converters(self):
         obj = GeneratedModelFieldWithConverters.objects.create(field=uuid.uuid4())
-        obj = self._refresh_if_needed(obj)
-        self.assertEqual(obj.field, obj.field_copy)
+        expected_num_queries = (
+            0 if connection.features.can_return_columns_from_insert else 1
+        )
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(obj.field, obj.field_copy)
+
+    def test_save_field_with_db_converters(self):
+        obj = GeneratedModelFieldWithConverters.objects.create(field=uuid.uuid4())
+        obj.field = uuid.uuid4()
+        expected_num_queries = (
+            0 if connection.features.can_return_rows_from_update else 1
+        )
+        obj.save(update_fields={"field"})
+        with self.assertNumQueries(expected_num_queries):
+            self.assertEqual(obj.field, obj.field_copy)
 
     def test_create_with_non_auto_pk(self):
         obj = GeneratedModelNonAutoPk.objects.create(id=1, a=2)