[5.0.x] Fixed #34936 -- Fixed migration crash for DecimalField with db_default on SQLite.

CAST() must be wrapped in parentheses to be recognized as an expression on SQLite.

Regression in 7414704e88.

Backport of 797957fb48 from main

django/db/backends/oracle/features.py

@@ -119,6 +119,10 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "Oracle doesn't support comparing NCLOB to NUMBER.": {
             "generic_relations_regress.tests.GenericRelationTests.test_textlink_filter",
         },
+        "DecimalField.db_default doesn't return decimal.Decimal instances on Oracle "
+        "(#34941).": {
+            "field_defaults.tests.DefaultTests.test_field_db_defaults_returning",
+        },
     }
     django_test_expected_failures = {
         # A bug in Django/oracledb with respect to string handling (#23843).

django/db/models/expressions.py

@@ -27,7 +27,7 @@ class SQLiteNumericMixin:
         sql, params = self.as_sql(compiler, connection, **extra_context)
         try:
             if self.output_field.get_internal_type() == "DecimalField":
-                sql = "CAST(%s AS NUMERIC)" % sql
+                sql = "(CAST(%s AS NUMERIC))" % sql
         except FieldError:
             pass
         return sql, params

tests/field_defaults/models.py

@@ -10,6 +10,7 @@ field.
 """
 
 from datetime import datetime
+from decimal import Decimal
 
 from django.db import models
 from django.db.models.functions import Coalesce, ExtractYear, Now, Pi
@@ -33,6 +34,9 @@ class DBArticle(models.Model):
 
     headline = models.CharField(max_length=100, db_default="Default headline")
     pub_date = models.DateTimeField(db_default=Now())
+    cost = models.DecimalField(
+        max_digits=3, decimal_places=2, db_default=Decimal("3.33")
+    )
 
     class Meta:
         required_db_features = {"supports_expression_defaults"}

tests/field_defaults/tests.py

@@ -1,4 +1,5 @@
 from datetime import datetime
+from decimal import Decimal
 from math import pi
 
 from django.db import connection
@@ -44,6 +45,7 @@ class DefaultTests(TestCase):
         self.assertIsInstance(a.id, int)
         self.assertEqual(a.headline, "Default headline")
         self.assertIsInstance(a.pub_date, datetime)
+        self.assertEqual(a.cost, Decimal("3.33"))
 
     @skipIfDBFeature("can_return_columns_from_insert")
     @skipUnlessDBFeature("supports_expression_defaults")
@@ -54,6 +56,7 @@ class DefaultTests(TestCase):
         self.assertIsInstance(a.id, int)
         self.assertEqual(a.headline, "Default headline")
         self.assertIsInstance(a.pub_date, datetime)
+        self.assertEqual(a.cost, Decimal("3.33"))
 
     def test_null_db_default(self):
         obj1 = DBDefaults.objects.create()
@@ -141,12 +144,12 @@ class DefaultTests(TestCase):
         articles = [DBArticle(pub_date=pub_date), DBArticle(pub_date=pub_date)]
         DBArticle.objects.bulk_create(articles)
 
-        headlines = DBArticle.objects.values_list("headline", "pub_date")
+        headlines = DBArticle.objects.values_list("headline", "pub_date", "cost")
         self.assertSequenceEqual(
             headlines,
             [
-                ("Default headline", pub_date),
-                ("Default headline", pub_date),
+                ("Default headline", pub_date, Decimal("3.33")),
+                ("Default headline", pub_date, Decimal("3.33")),
             ],
         )