db: Replace use of Executable.scalar(), Executable.execute()

Resolve the following RemovedIn20Warning warnings:

  The Executable.scalar() method is considered legacy as of the 1.x
  series of SQLAlchemy and will be removed in 2.0. Scalar execution in
  SQLAlchemy 2.0 is performed by the Connection.scalar() method of
  Connection, or in the ORM by the Session.scalar() method of Session.

  The Executable.execute() method is considered legacy as of the 1.x
  series of SQLAlchemy and will be removed in 2.0. All statement
  execution in SQLAlchemy 2.0 is performed by the Connection.execute()
  method of Connection, or in the ORM by the Session.execute() method of
  Session.

Note that while we're resolving these issues, we also head off other
issues that are currently ignored but will ultimately need to be
resolved such as switching to the modern calling style of 'select()'

Change-Id: Idebcba02a6704df21e5520fdbf60296b8187e79c
Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin

nova/cmd/status.py

@@ -87,10 +87,15 @@ def _count_compute_nodes(self, context=None):
         # table, or by only counting compute nodes with a service version of at
         # least 15 which was the highest service version when Newton was
         # released.
-        meta = sa.MetaData(bind=main_db_api.get_engine(context=context))
-        compute_nodes = sa.Table('compute_nodes', meta, autoload=True)
-        return sa.select([sqlfunc.count()]).select_from(compute_nodes).where(
-            compute_nodes.c.deleted == 0).scalar()
+        meta = sa.MetaData()
+        engine = main_db_api.get_engine(context=context)
+        compute_nodes = sa.Table('compute_nodes', meta, autoload_with=engine)
+        with engine.connect() as conn:
+            return conn.execute(
+                sa.select(sqlfunc.count()).select_from(compute_nodes).where(
+                    compute_nodes.c.deleted == 0
+                )
+            ).scalars().first()
 
     def _check_cellsv2(self):
         """Checks to see if cells v2 has been setup.
@@ -104,7 +109,7 @@ def _check_cellsv2(self):
         for compute nodes if there are no host mappings on a fresh install.
         """
         meta = sa.MetaData()
-        meta.bind = api_db_api.get_engine()
+        engine = api_db_api.get_engine()
 
         cell_mappings = self._get_cell_mappings()
         count = len(cell_mappings)
@@ -123,9 +128,13 @@ def _check_cellsv2(self):
                     'retry.')
             return upgradecheck.Result(upgradecheck.Code.FAILURE, msg)
 
-        host_mappings = sa.Table('host_mappings', meta, autoload=True)
-        count = sa.select([sqlfunc.count()]).select_from(host_mappings)\
-            .scalar()
+        host_mappings = sa.Table('host_mappings', meta, autoload_with=engine)
+
+        with engine.connect() as conn:
+            count = conn.execute(
+                sa.select(sqlfunc.count()).select_from(host_mappings)
+            ).scalars().first()
+
         if count == 0:
             # This may be a fresh install in which case there may not be any
             # compute_nodes in the cell database if the nova-compute service

nova/tests/fixtures/nova.py

@@ -925,18 +925,6 @@ def setUp(self):
             message=r'Using strings to indicate relationship names .*',
             category=sqla_exc.SADeprecationWarning)
 
-        warnings.filterwarnings(
-            'ignore',
-            module='nova',
-            message=r'The Executable.execute\(\) method is considered .*',
-            category=sqla_exc.SADeprecationWarning)
-
-        warnings.filterwarnings(
-            'ignore',
-            module='nova',
-            message=r'The Executable.scalar\(\) method is considered .*',
-            category=sqla_exc.SADeprecationWarning)
-
         warnings.filterwarnings(
             'ignore',
             module='nova',