Modernize use of table.count() with func.count()

The table.count() function in SQLAlchemy has been deprecated
since version 1.1 [1] and is being removed in version 1.4 [2] [3].
In order to maintain forwards compatibility as well as
suit SQLAlchemy's CI that includes oslo.db, replace this
one usage with modern use of func.count() as well as
explicit connection execution (engine.execute() is also
going away more long term).

[1] https://docs.sqlalchemy.org/en/13/core/selectable.html?highlight=fromclause%20count#sqlalchemy.sql.expression.FromClause.count
[2] https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/1833
[3] https://github.com/sqlalchemy/sqlalchemy/issues/4643

Change-Id: I2e4b9082194df6d916000c4f8f179f05d606e1a3

1 files changed, 10 insertions, 4 deletions

diff --git a/oslo_db/tests/sqlalchemy/test_sqlalchemy.py b/oslo_db/tests/sqlalchemy/test_sqlalchemy.py
index bde7303..c60ee74 100644
--- a/oslo_db/tests/sqlalchemy/test_sqlalchemy.py
+++ b/oslo_db/tests/sqlalchemy/test_sqlalchemy.py
@@ -115,10 +115,16 @@ class SQLiteSavepointTest(test_base._DbTestCase):
             ).fetchall()
         )
         trans.rollback()
-        self.assertEqual(
-            0,
-            self.engine.scalar(self.test_table.count())
-        )
+
+        with self.engine.connect() as conn:
+            self.assertEqual(
+                0,
+                conn.scalar(
+                    sqlalchemy.select(
+                        [sqlalchemy.func.count(self.test_table.c.id)],
+                    ).select_from(self.test_table)
+                )
+            )
 
     def test_savepoint_middle(self):
         with self.engine.begin() as conn: