Get test suite to full pass with SQLAlchemy 2.0

Remaining issues encountered when running with SQLAlchemy 2.0 for real:

* Never call str() on a URL and expect it to be meaningful anymore.
  The password is aggressively obfuscated now (users absolultely
  wouldn't let us leave it as is)
* More utilities and fixtures that were calling begin() within a
  block that would have already begun
* isnot is now called is_not; mocking "isnot" leads into too many
  weird compat layers
* ORM InstrumentedAttribute and internals use __slots__ now, mock
  seems to not be able to patch methods.  Ideally these tests would use
  a comparator subclass or something
* Connection.connection.connection is now called driver_connection,
  SQLAlchemy keeps the old name available however oslo.db test suite
  does not appear to tolerate the deprecation warning emitted,
  so add a compat layer
* mapper() is fully removed from 2.0, not sure if there is another
  not-yet-committed gerrit that removes mapper()

[1] https://docs.sqlalchemy.org/en/20/core/engines.html#sqlalchemy.create_engine.params.pool_pre_ping
[2] https://docs.sqlalchemy.org/en/20/changelog/changelog_20.html#change-2fe37eaf2295cebd3bb4ee8e5b8c575c
[3] https://github.com/sqlalchemy/sqlalchemy/issues/5648

Change-Id: Ifaca67c07f008d8bc0febeecd3e200cc7ee7a4b0

12 files changed, 251 insertions, 153 deletions

diff --git a/oslo_db/sqlalchemy/compat/__init__.py b/oslo_db/sqlalchemy/compat/__init__.py
new file mode 100644
index 0000000..6713696
--- /dev/null
+++ b/oslo_db/sqlalchemy/compat/__init__.py
@@ -0,0 +1,36 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from oslo_utils import versionutils
+
+from sqlalchemy import __version__
+
+
+_vers = versionutils.convert_version_to_tuple(__version__)
+sqla_2 = _vers >= (2, )
+
+
+def dialect_from_exception_context(ctx):
+    if sqla_2:
+        # SQLAlchemy 2.0 still has context.engine, however if the
+        # exception context is called in the context of a ping handler,
+        # engine is not present.  need to use dialect instead
+        return ctx.dialect
+    else:
+        return ctx.engine.dialect
+
+
+def driver_connection(connection):
+    if sqla_2:
+        return connection.connection.driver_connection
+    else:
+        return connection.connection.connection
diff --git a/oslo_db/sqlalchemy/enginefacade.py b/oslo_db/sqlalchemy/enginefacade.py
index 3a316b3..39fb061 100644
--- a/oslo_db/sqlalchemy/enginefacade.py
+++ b/oslo_db/sqlalchemy/enginefacade.py
@@ -164,7 +164,6 @@ class _TransactionFactory(object):
         }
         self._maker_cfg = {
             'expire_on_commit': _Default(False),
-            '__autocommit': False,
         }
         self._transaction_ctx_cfg = {
             'rollback_reader_sessions': False,
@@ -468,7 +467,6 @@ class _TransactionFactory(object):
 
     def _maker_args_for_conf(self, conf):
         maker_args = self._args_for_conf(self._maker_cfg, conf)
-        maker_args['autocommit'] = maker_args.pop('__autocommit')
         return maker_args
 
     def dispose_pool(self):
@@ -1238,9 +1236,6 @@ class LegacyEngineFacade(object):
     :param sqlite_fk: enable foreign keys in SQLite
     :type sqlite_fk: bool
 
-    :param autocommit: use autocommit mode for created Session instances
-    :type autocommit: bool
-
     :param expire_on_commit: expire session objects on commit
     :type expire_on_commit: bool
 
@@ -1282,22 +1277,14 @@ class LegacyEngineFacade(object):
 
     """
     def __init__(self, sql_connection, slave_connection=None,
-                 sqlite_fk=False, autocommit=False,
-                 expire_on_commit=False, _conf=None, _factory=None, **kwargs):
+                 sqlite_fk=False, expire_on_commit=False, _conf=None,
+                 _factory=None, **kwargs):
         warnings.warn(
             "EngineFacade is deprecated; please use "
             "oslo_db.sqlalchemy.enginefacade",
             warning.OsloDBDeprecationWarning,
             stacklevel=2)
 
-        if autocommit is True:
-            warnings.warn(
-                'autocommit support will be removed in SQLAlchemy 2.0 and '
-                'should not be relied on; please rework your code to remove '
-                'reliance on this feature',
-                warning.OsloDBDeprecationWarning,
-                stacklevel=2)
-
         if _factory:
             self._factory = _factory
         else:
@@ -1305,7 +1292,6 @@ class LegacyEngineFacade(object):
 
             self._factory.configure(
                 sqlite_fk=sqlite_fk,
-                __autocommit=autocommit,
                 expire_on_commit=expire_on_commit,
                 **kwargs
             )
@@ -1371,7 +1357,7 @@ class LegacyEngineFacade(object):
 
     @classmethod
     def from_config(cls, conf,
-                    sqlite_fk=False, autocommit=False, expire_on_commit=False):
+                    sqlite_fk=False, expire_on_commit=False):
         """Initialize EngineFacade using oslo.config config instance options.
 
         :param conf: oslo.config config instance
@@ -1380,9 +1366,6 @@ class LegacyEngineFacade(object):
         :param sqlite_fk: enable foreign keys in SQLite
         :type sqlite_fk: bool
 
-        :param autocommit: use autocommit mode for created Session instances
-        :type autocommit: bool
-
         :param expire_on_commit: expire session objects on commit
         :type expire_on_commit: bool
 
@@ -1391,5 +1374,4 @@ class LegacyEngineFacade(object):
         return cls(
             None,
             sqlite_fk=sqlite_fk,
-            autocommit=autocommit,
             expire_on_commit=expire_on_commit, _conf=conf)
diff --git a/oslo_db/sqlalchemy/engines.py b/oslo_db/sqlalchemy/engines.py
index 4634ce5..146d189 100644
--- a/oslo_db/sqlalchemy/engines.py
+++ b/oslo_db/sqlalchemy/engines.py
@@ -16,6 +16,7 @@
 """Core SQLAlchemy connectivity routines.
 """
 
+import functools
 import itertools
 import logging
 import os
@@ -29,10 +30,11 @@ import sqlalchemy
 from sqlalchemy import event
 from sqlalchemy import exc
 from sqlalchemy import pool
-from sqlalchemy.sql.expression import select
+from sqlalchemy import select
 
 from oslo_db import exception
 
+from oslo_db.sqlalchemy import compat
 from oslo_db.sqlalchemy import exc_filters
 from oslo_db.sqlalchemy import ndb
 from oslo_db.sqlalchemy import utils
@@ -57,6 +59,7 @@ def _connect_ping_listener(connection, branch):
 
     Ping the server at transaction begin and transparently reconnect
     if a disconnect exception occurs.
+
     """
     if branch:
         return
@@ -94,6 +97,14 @@ def _connect_ping_listener(connection, branch):
             connection.rollback()
 
 
+# SQLAlchemy 2.0 is compatible here, however oslo.db's test suite
+# raises for all deprecation errors, so we have to check for 2.0
+# and wrap out a parameter that is deprecated
+if compat.sqla_2:
+    _connect_ping_listener = functools.partial(
+        _connect_ping_listener, branch=False)
+
+
 def _setup_logging(connection_debug=0):
     """setup_logging function maps SQL debug level to Python log level.
 
@@ -189,7 +200,7 @@ def create_engine(sql_connection, sqlite_fk=False, mysql_sql_mode=None,
     _vet_url(url)
 
     engine_args = {
-        "pool_recycle": connection_recycle_time,
+        'pool_recycle': connection_recycle_time,
         'connect_args': {},
         'logging_name': logging_name
     }
@@ -198,11 +209,13 @@ def create_engine(sql_connection, sqlite_fk=False, mysql_sql_mode=None,
 
     _init_connection_args(
         url, engine_args,
-        max_pool_size=max_pool_size,
-        max_overflow=max_overflow,
-        pool_timeout=pool_timeout,
-        json_serializer=json_serializer,
-        json_deserializer=json_deserializer,
+        dict(
+            max_pool_size=max_pool_size,
+            max_overflow=max_overflow,
+            pool_timeout=pool_timeout,
+            json_serializer=json_serializer,
+            json_deserializer=json_deserializer,
+        )
     )
 
     engine = sqlalchemy.create_engine(url, **engine_args)
@@ -224,6 +237,7 @@ def create_engine(sql_connection, sqlite_fk=False, mysql_sql_mode=None,
     exc_filters.register_engine(engine)
 
     # register engine connect handler
+
     event.listen(engine, "engine_connect", _connect_ping_listener)
 
     # initial connect + test
@@ -237,9 +251,16 @@ def create_engine(sql_connection, sqlite_fk=False, mysql_sql_mode=None,
 
 
 @utils.dispatch_for_dialect('*', multiple=True)
-def _init_connection_args(
-    url, engine_args,
-    max_pool_size=None, max_overflow=None, pool_timeout=None, **kw):
+def _init_connection_args(url, engine_args, kw):
+
+    # (zzzeek) kw is passed by reference rather than as **kw so that the
+    # init_connection_args routines can modify the contents of what
+    # will be passed to create_engine, including removing arguments that
+    # don't apply.  This allows things such as replacing QueuePool with
+    # NUllPool, for example, as the latter pool would reject these parameters.
+    max_pool_size = kw.get("max_pool_size", None)
+    max_overflow = kw.get("max_overflow", None)
+    pool_timeout = kw.get("pool_timeout", None)
 
     pool_class = url.get_dialect().get_pool_class(url)
     if issubclass(pool_class, pool.QueuePool):
@@ -252,17 +273,25 @@ def _init_connection_args(
 
 
 @_init_connection_args.dispatch_for("sqlite")
-def _init_connection_args(url, engine_args, **kw):
+def _init_connection_args(url, engine_args, kw):
     pool_class = url.get_dialect().get_pool_class(url)
-    # singletonthreadpool is used for :memory: connections;
-    # replace it with StaticPool.
     if issubclass(pool_class, pool.SingletonThreadPool):
+        # singletonthreadpool is used for :memory: connections;
+        # replace it with StaticPool.
         engine_args["poolclass"] = pool.StaticPool
         engine_args['connect_args']['check_same_thread'] = False
+    elif issubclass(pool_class, pool.QueuePool):
+        # SQLAlchemy 2.0 uses QueuePool for sqlite file DBs; put NullPool
+        # back to avoid compatibility issues
+        kw.pop("max_pool_size", None)
+        kw.pop("max_overflow", None)
+        engine_args.pop("max_pool_size", None)
+        engine_args.pop("max_overflow", None)
+        engine_args["poolclass"] = pool.NullPool
 
 
 @_init_connection_args.dispatch_for("postgresql")
-def _init_connection_args(url, engine_args, **kw):
+def _init_connection_args(url, engine_args, kw):
     if 'client_encoding' not in url.query:
         # Set encoding using engine_args instead of connect_args since
         # it's supported for PostgreSQL 8.*. More details at:
@@ -273,13 +302,13 @@ def _init_connection_args(url, engine_args, **kw):
 
 
 @_init_connection_args.dispatch_for("mysql")
-def _init_connection_args(url, engine_args, **kw):
+def _init_connection_args(url, engine_args, kw):
     if 'charset' not in url.query:
         engine_args['connect_args']['charset'] = 'utf8'
 
 
 @_init_connection_args.dispatch_for("mysql+mysqlconnector")
-def _init_connection_args(url, engine_args, **kw):
+def _init_connection_args(url, engine_args, kw):
     # mysqlconnector engine (<1.0) incorrectly defaults to
     # raise_on_warnings=True
     #  https://bitbucket.org/zzzeek/sqlalchemy/issue/2515
@@ -288,8 +317,7 @@ def _init_connection_args(url, engine_args, **kw):
 
 
 @_init_connection_args.dispatch_for("mysql+mysqldb")
-@_init_connection_args.dispatch_for("mysql+oursql")
-def _init_connection_args(url, engine_args, **kw):
+def _init_connection_args(url, engine_args, kw):
     # Those drivers require use_unicode=0 to avoid performance drop due
     # to internal usage of Python unicode objects in the driver
     #  http://docs.sqlalchemy.org/en/rel_0_9/dialects/mysql.html
@@ -444,7 +472,6 @@ def _add_process_guards(engine):
                 "database connection, "
                 "which is being discarded and recreated.",
                 {"newproc": pid, "orig": connection_record.info['pid']})
-            connection_record.connection = connection_proxy.connection = None
             raise exc.DisconnectionError(
                 "Connection record belongs to pid %s, "
                 "attempting to check out in pid %s" %
diff --git a/oslo_db/sqlalchemy/provision.py b/oslo_db/sqlalchemy/provision.py
index a4830b6..a6cc527 100644
--- a/oslo_db/sqlalchemy/provision.py
+++ b/oslo_db/sqlalchemy/provision.py
@@ -241,7 +241,6 @@ class Backend(object):
         :raises: ``BackendNotAvailable`` if the backend is not available.
 
         """
-
         if not self.verified:
             try:
                 eng = self._ensure_backend_available(self.url)
@@ -493,7 +492,6 @@ class BackendImpl(object, metaclass=abc.ABCMeta):
         then emit a command to switch to the named database.
 
         """
-
         url = utils.make_url(base_url)
 
         # TODO(zzzeek): remove hasattr() conditional in favor of "url.set()"
@@ -515,16 +513,14 @@ class MySQLBackendImpl(BackendImpl):
         return "mysql+pymysql://openstack_citest:openstack_citest@localhost/"
 
     def create_named_database(self, engine, ident, conditional=False):
-        with engine.connect() as conn:
+        with engine.begin() as conn:
             if not conditional or not self.database_exists(conn, ident):
-                with conn.begin():
-                    conn.exec_driver_sql("CREATE DATABASE %s" % ident)
+                conn.exec_driver_sql("CREATE DATABASE %s" % ident)
 
     def drop_named_database(self, engine, ident, conditional=False):
-        with engine.connect() as conn:
+        with engine.begin() as conn:
             if not conditional or self.database_exists(conn, ident):
-                with conn.begin():
-                    conn.exec_driver_sql("DROP DATABASE %s" % ident)
+                conn.exec_driver_sql("DROP DATABASE %s" % ident)
 
     def database_exists(self, engine, ident):
         s = sql.text("SHOW DATABASES LIKE :ident")
@@ -585,19 +581,17 @@ class PostgresqlBackendImpl(BackendImpl):
             isolation_level="AUTOCOMMIT",
         ) as conn:
             if not conditional or not self.database_exists(conn, ident):
-                with conn.begin():
-                    conn.exec_driver_sql("CREATE DATABASE %s" % ident)
+                conn.exec_driver_sql("CREATE DATABASE %s" % ident)
 
     def drop_named_database(self, engine, ident, conditional=False):
         with engine.connect().execution_options(
             isolation_level="AUTOCOMMIT",
         ) as conn:
             self._close_out_database_users(conn, ident)
-            with conn.begin():
-                if conditional:
-                    conn.exec_driver_sql("DROP DATABASE IF EXISTS %s" % ident)
-                else:
-                    conn.exec_driver_sql("DROP DATABASE %s" % ident)
+            if conditional:
+                conn.exec_driver_sql("DROP DATABASE IF EXISTS %s" % ident)
+            else:
+                conn.exec_driver_sql("DROP DATABASE %s" % ident)
 
     def drop_additional_objects(self, conn):
         enums = [e['name'] for e in sqlalchemy.inspect(conn).get_enums()]
diff --git a/oslo_db/sqlalchemy/update_match.py b/oslo_db/sqlalchemy/update_match.py
index 559aa78..c2dd8d6 100644
--- a/oslo_db/sqlalchemy/update_match.py
+++ b/oslo_db/sqlalchemy/update_match.py
@@ -393,8 +393,8 @@ def update_returning_pk(query, values, surrogate_key):
     mapper = inspect(entity).mapper
     session = query.session
 
-    bind = session.connection(mapper=mapper)
-    if bind.dialect.implicit_returning:
+    bind = session.connection(bind_arguments=dict(mapper=mapper))
+    if bind.dialect.name == "postgresql":
         pk_strategy = _pk_strategy_returning
     elif bind.dialect.name == 'mysql' and \
         len(mapper.primary_key) == 1 and \
diff --git a/oslo_db/sqlalchemy/utils.py b/oslo_db/sqlalchemy/utils.py
index b539b6d..58b2486 100644
--- a/oslo_db/sqlalchemy/utils.py
+++ b/oslo_db/sqlalchemy/utils.py
@@ -213,7 +213,7 @@ def paginate_query(query, model, limit, sort_keys, marker=None,
             null_order_by_stmt = {
                 "": None,
                 "nullsfirst": sort_key_attr.is_(None),
-                "nullslast": sort_key_attr.isnot(None),
+                "nullslast": sort_key_attr.is_not(None),
             }[null_sort_dir]
         except KeyError:
             raise ValueError(_("Unknown sort direction, "
@@ -1016,26 +1016,29 @@ def suspend_fk_constraints_for_col_alter(
         yield
     else:
         with engine.connect() as conn:
-            insp = inspect(conn)
-            fks = []
-            for ref_table_name in referents:
-                for fk in insp.get_foreign_keys(ref_table_name):
-                    if not fk.get('name'):
-                        raise AssertionError("foreign key hasn't a name.")
-                    if fk['referred_table'] == table_name and \
-                            column_name in fk['referred_columns']:
-                        fk['source_table'] = ref_table_name
-                        if 'options' not in fk:
-                            fk['options'] = {}
-                        fks.append(fk)
-
-            ctx = MigrationContext.configure(conn)
-            op = Operations(ctx)
-
             with conn.begin():
+                insp = inspect(conn)
+                fks = []
+                for ref_table_name in referents:
+                    for fk in insp.get_foreign_keys(ref_table_name):
+                        if not fk.get('name'):
+                            raise AssertionError("foreign key hasn't a name.")
+                        if fk['referred_table'] == table_name and \
+                                column_name in fk['referred_columns']:
+                            fk['source_table'] = ref_table_name
+                            if 'options' not in fk:
+                                fk['options'] = {}
+                            fks.append(fk)
+
+                ctx = MigrationContext.configure(conn)
+                op = Operations(ctx)
+
                 for fk in fks:
                     op.drop_constraint(
-                        fk['name'], fk['source_table'], type_="foreignkey")
+                        fk['name'],
+                        fk['source_table'],
+                        type_="foreignkey",
+                    )
 
             yield
 
diff --git a/oslo_db/tests/sqlalchemy/test_enginefacade.py b/oslo_db/tests/sqlalchemy/test_enginefacade.py
index 4175880..c2b980f 100644
--- a/oslo_db/tests/sqlalchemy/test_enginefacade.py
+++ b/oslo_db/tests/sqlalchemy/test_enginefacade.py
@@ -357,11 +357,11 @@ class MockFacadeTest(test_base.BaseTestCase):
         maker_factories = mock.Mock(side_effect=get_maker)
 
         maker_factories(
-            autocommit=False, engine=engines.writer,
+            engine=engines.writer,
             expire_on_commit=False)
         if self.slave_uri:
             maker_factories(
-                autocommit=False, engine=engines.async_reader,
+                engine=engines.async_reader,
                 expire_on_commit=False)
 
         yield makers
diff --git a/oslo_db/tests/sqlalchemy/test_exc_filters.py b/oslo_db/tests/sqlalchemy/test_exc_filters.py
index 7f64594..af3cd91 100644
--- a/oslo_db/tests/sqlalchemy/test_exc_filters.py
+++ b/oslo_db/tests/sqlalchemy/test_exc_filters.py
@@ -26,6 +26,7 @@ from sqlalchemy.orm import registry
 from sqlalchemy import sql
 
 from oslo_db import exception
+from oslo_db.sqlalchemy import compat
 from oslo_db.sqlalchemy import engines
 from oslo_db.sqlalchemy import exc_filters
 from oslo_db.sqlalchemy import utils
@@ -139,18 +140,29 @@ class TestsExceptionFilter(_SQLAExceptionMatcher, test_base.BaseTestCase):
         # statement
         self.engine.connect().close()
 
-        with test_utils.nested(
+        patches = [
             mock.patch.object(engine.dialect, "do_execute", do_execute),
             # replace the whole DBAPI rather than patching "Error"
             # as some DBAPIs might not be patchable (?)
             mock.patch.object(engine.dialect,
                               "dbapi",
                               mock.Mock(Error=self.Error)),
+
             mock.patch.object(engine.dialect, "name", dialect_name),
             mock.patch.object(engine.dialect,
                               "is_disconnect",
                               lambda *args: is_disconnect)
-        ):
+        ]
+        if compat.sqla_2:
+            patches.append(
+                mock.patch.object(
+                    engine.dialect,
+                    "loaded_dbapi",
+                    mock.Mock(Error=self.Error),
+                )
+            )
+
+        with test_utils.nested(*patches):
             yield
 
     def _run_test(self, dialect_name, statement, raises, expected,
@@ -754,7 +766,7 @@ class TestExceptionCauseMySQLSavepoint(
             session.execute(sql.text("select 1"))
 
             # close underying DB connection
-            session.connection().connection.connection.close()
+            compat.driver_connection(session.connection()).close()
 
             # alternate approach, but same idea:
             # conn_id = session.scalar("select connection_id()")
@@ -779,7 +791,7 @@ class TestExceptionCauseMySQLSavepoint(
             session.execute(sql.text("select 1"))
 
             # close underying DB connection
-            session.connection().connection.connection.close()
+            compat.driver_connection(session.connection()).close()
 
             # alternate approach, but same idea:
             # conn_id = session.scalar("select connection_id()")
@@ -947,8 +959,8 @@ class TestDuplicate(TestsExceptionFilter):
 class TestDeadlock(TestsExceptionFilter):
     statement = ('SELECT quota_usages.created_at AS '
                  'quota_usages_created_at FROM quota_usages '
-                 'WHERE quota_usages.project_id = %(project_id_1)s '
-                 'AND quota_usages.deleted = %(deleted_1)s FOR UPDATE')
+                 'WHERE quota_usages.project_id = :project_id_1 '
+                 'AND quota_usages.deleted = :deleted_1 FOR UPDATE')
     params = {
         'project_id_1': '8891d4478bbf48ad992f050cdf55e9b5',
         'deleted_1': 0
diff --git a/oslo_db/tests/sqlalchemy/test_provision.py b/oslo_db/tests/sqlalchemy/test_provision.py
index a6cedce..e0ab39f 100644
--- a/oslo_db/tests/sqlalchemy/test_provision.py
+++ b/oslo_db/tests/sqlalchemy/test_provision.py
@@ -13,6 +13,7 @@
 import os
 from unittest import mock
 
+from sqlalchemy.engine import url as sqla_url
 from sqlalchemy import exc as sa_exc
 from sqlalchemy import inspect
 from sqlalchemy import schema
@@ -156,8 +157,8 @@ class AdHocURLTest(test_base.BaseTestCase):
         fixture.setUp()
 
         self.assertEqual(
-            str(enginefacade._context_manager._factory._writer_engine.url),
-            "sqlite:///foo.db"
+            enginefacade._context_manager._factory._writer_engine.url,
+            sqla_url.make_url("sqlite:///foo.db")
             )
 
         self.assertTrue(os.path.exists("foo.db"))
@@ -176,14 +177,14 @@ class AdHocURLTest(test_base.BaseTestCase):
         self.addCleanup(
             mysql_backend.drop_named_database, "adhoc_test"
         )
-        url = str(mysql_backend.provisioned_database_url("adhoc_test"))
+        url = mysql_backend.provisioned_database_url("adhoc_test")
 
         fixture = test_fixtures.AdHocDbFixture(url)
 
         fixture.setUp()
 
         self.assertEqual(
-            str(enginefacade._context_manager._factory._writer_engine.url),
+            enginefacade._context_manager._factory._writer_engine.url,
             url
         )
 
diff --git a/oslo_db/tests/sqlalchemy/test_sqlalchemy.py b/oslo_db/tests/sqlalchemy/test_sqlalchemy.py
index a51d2cb..5f7b27f 100644
--- a/oslo_db/tests/sqlalchemy/test_sqlalchemy.py
+++ b/oslo_db/tests/sqlalchemy/test_sqlalchemy.py
@@ -23,10 +23,10 @@ from unittest import mock
 
 import fixtures
 from oslo_config import cfg
-from oslo_utils import versionutils
 import sqlalchemy
 from sqlalchemy.engine import base as base_engine
 from sqlalchemy import exc
+from sqlalchemy.pool import NullPool
 from sqlalchemy import sql
 from sqlalchemy import Column, MetaData, Table
 from sqlalchemy import Integer, String
@@ -34,6 +34,7 @@ from sqlalchemy.orm import declarative_base
 
 from oslo_db import exception
 from oslo_db import options as db_options
+from oslo_db.sqlalchemy import compat
 from oslo_db.sqlalchemy import enginefacade
 from oslo_db.sqlalchemy import engines
 from oslo_db.sqlalchemy import models
@@ -388,9 +389,8 @@ class EngineFacadeTestCase(test_base.BaseTestCase):
         self.assertIsNot(ses1, ses2)
 
     def test_get_session_arguments_override_default_settings(self):
-        ses = self.facade.get_session(autocommit=False, expire_on_commit=True)
+        ses = self.facade.get_session(expire_on_commit=True)
 
-        self.assertFalse(ses.autocommit)
         self.assertTrue(ses.expire_on_commit)
 
     @mock.patch('oslo_db.sqlalchemy.orm.get_maker')
@@ -410,7 +410,6 @@ class EngineFacadeTestCase(test_base.BaseTestCase):
             conf.set_override(optname, optvalue, group='database')
 
         session.EngineFacade.from_config(conf,
-                                         autocommit=False,
                                          expire_on_commit=True)
 
         create_engine.assert_called_once_with(
@@ -435,7 +434,6 @@ class EngineFacadeTestCase(test_base.BaseTestCase):
             logging_name=mock.ANY,
         )
         get_maker.assert_called_once_with(engine=create_engine(),
-                                          autocommit=False,
                                           expire_on_commit=True)
 
     def test_slave_connection(self):
@@ -696,22 +694,24 @@ class CreateEngineTest(test_base.BaseTestCase):
 
     def test_queuepool_args(self):
         engines._init_connection_args(
-            utils.make_url("mysql+pymysql://u:p@host/test"), self.args,
-            max_pool_size=10, max_overflow=10)
+            utils.make_url("mysql+pymysql://u:p@host/test"),
+            self.args,
+            {'max_pool_size': 10, 'max_overflow': 10},
+        )
         self.assertEqual(10, self.args['pool_size'])
         self.assertEqual(10, self.args['max_overflow'])
 
     def test_sqlite_memory_pool_args(self):
         for _url in ("sqlite://", "sqlite:///:memory:"):
             engines._init_connection_args(
-                utils.make_url(_url), self.args,
-                max_pool_size=10, max_overflow=10)
+                utils.make_url(_url),
+                self.args,
+                {'max_pool_size': 10, 'max_overflow': 10},
+            )
 
-            # queuepool arguments are not peresnet
-            self.assertNotIn(
-                'pool_size', self.args)
-            self.assertNotIn(
-                'max_overflow', self.args)
+            # queuepool arguments are not present
+            self.assertNotIn('pool_size', self.args)
+            self.assertNotIn('max_overflow', self.args)
 
             self.assertEqual(False,
                              self.args['connect_args']['check_same_thread'])
@@ -721,8 +721,10 @@ class CreateEngineTest(test_base.BaseTestCase):
 
     def test_sqlite_file_pool_args(self):
         engines._init_connection_args(
-            utils.make_url("sqlite:///somefile.db"), self.args,
-            max_pool_size=10, max_overflow=10)
+            utils.make_url("sqlite:///somefile.db"),
+            self.args,
+            {'max_pool_size': 10, 'max_overflow': 10},
+        )
 
         # queuepool arguments are not peresnet
         self.assertNotIn('pool_size', self.args)
@@ -731,9 +733,12 @@ class CreateEngineTest(test_base.BaseTestCase):
 
         self.assertFalse(self.args['connect_args'])
 
-        # NullPool is the default for file based connections,
-        # no need to specify this
-        self.assertNotIn('poolclass', self.args)
+        if not compat.sqla_2:
+            # NullPool is the default for file based connections,
+            # no need to specify this
+            self.assertNotIn('poolclass', self.args)
+        else:
+            self.assertIs(self.args["poolclass"], NullPool)
 
     def _test_mysql_connect_args_default(self, connect_args):
         self.assertEqual({'charset': 'utf8', 'use_unicode': 1},
@@ -741,34 +746,29 @@ class CreateEngineTest(test_base.BaseTestCase):
 
     def test_mysql_connect_args_default(self):
         engines._init_connection_args(
-            utils.make_url("mysql://u:p@host/test"), self.args)
-        self._test_mysql_connect_args_default(self.args['connect_args'])
-
-    def test_mysql_oursql_connect_args_default(self):
-        engines._init_connection_args(
-            utils.make_url("mysql+oursql://u:p@host/test"), self.args)
+            utils.make_url("mysql://u:p@host/test"), self.args, {})
         self._test_mysql_connect_args_default(self.args['connect_args'])
 
     def test_mysql_pymysql_connect_args_default(self):
         engines._init_connection_args(
-            utils.make_url("mysql+pymysql://u:p@host/test"), self.args)
+            utils.make_url("mysql+pymysql://u:p@host/test"), self.args, {})
         self.assertEqual({'charset': 'utf8'}, self.args['connect_args'])
 
     def test_mysql_mysqldb_connect_args_default(self):
         engines._init_connection_args(
-            utils.make_url("mysql+mysqldb://u:p@host/test"), self.args)
+            utils.make_url("mysql+mysqldb://u:p@host/test"), self.args, {})
         self._test_mysql_connect_args_default(self.args['connect_args'])
 
     def test_postgresql_connect_args_default(self):
         engines._init_connection_args(
-            utils.make_url("postgresql://u:p@host/test"), self.args)
+            utils.make_url("postgresql://u:p@host/test"), self.args, {})
         self.assertEqual('utf8', self.args['client_encoding'])
         self.assertFalse(self.args['connect_args'])
 
     def test_mysqlconnector_raise_on_warnings_default(self):
         engines._init_connection_args(
             utils.make_url("mysql+mysqlconnector://u:p@host/test"),
-            self.args)
+            self.args, {})
         self.assertEqual(False, self.args['connect_args']['raise_on_warnings'])
 
     def test_mysqlconnector_raise_on_warnings_override(self):
@@ -776,7 +776,7 @@ class CreateEngineTest(test_base.BaseTestCase):
             utils.make_url(
                 "mysql+mysqlconnector://u:p@host/test"
                 "?raise_on_warnings=true"),
-            self.args
+            self.args, {}
         )
 
         self.assertNotIn('raise_on_warnings', self.args['connect_args'])
@@ -851,18 +851,18 @@ class ProcessGuardTest(db_test_base._DbTestCase):
 
         with mock.patch("os.getpid", get_parent_pid):
             with self.engine.connect() as conn:
-                dbapi_id = id(conn.connection.connection)
+                dbapi_id = id(compat.driver_connection(conn))
 
         with mock.patch("os.getpid", get_child_pid):
             with self.engine.connect() as conn:
-                new_dbapi_id = id(conn.connection.connection)
+                new_dbapi_id = id(compat.driver_connection(conn))
 
         self.assertNotEqual(dbapi_id, new_dbapi_id)
 
         # ensure it doesn't trip again
         with mock.patch("os.getpid", get_child_pid):
             with self.engine.connect() as conn:
-                newer_dbapi_id = id(conn.connection.connection)
+                newer_dbapi_id = id(compat.driver_connection(conn))
 
         self.assertEqual(new_dbapi_id, newer_dbapi_id)
 
@@ -906,13 +906,12 @@ class MySQLConnectPingListenerTest(db_test_base._MySQLOpportunisticTestCase):
             with self.engine.begin() as conn:
                 self.assertTrue(isinstance(conn._transaction,
                                            base_engine.RootTransaction))
-                engines._connect_ping_listener(conn, False)
                 # TODO(ralonsoh): drop this check once SQLAlchemy minimum
                 #  version is 2.0.
-                sqla_version = versionutils.convert_version_to_tuple(
-                    sqlalchemy.__version__)
-                if sqla_version[0] >= 2:
+                if compat.sqla_2:
+                    engines._connect_ping_listener(conn)
                     self.assertIsNone(conn._transaction)
                 else:
+                    engines._connect_ping_listener(conn, False)
                     self.assertTrue(isinstance(conn._transaction,
                                                base_engine.RootTransaction))
diff --git a/oslo_db/tests/sqlalchemy/test_utils.py b/oslo_db/tests/sqlalchemy/test_utils.py
index c78ec06..059d015 100644
--- a/oslo_db/tests/sqlalchemy/test_utils.py
+++ b/oslo_db/tests/sqlalchemy/test_utils.py
@@ -26,7 +26,7 @@ from sqlalchemy.dialects.postgresql import psycopg2
 from sqlalchemy.exc import OperationalError
 from sqlalchemy.ext.hybrid import hybrid_property
 from sqlalchemy.orm import declarative_base
-from sqlalchemy.orm import mapper
+from sqlalchemy.orm import registry
 from sqlalchemy.orm import Session
 from sqlalchemy import PrimaryKeyConstraint
 from sqlalchemy import sql
@@ -131,7 +131,8 @@ fake_table = Table(
     Column('key', String(50))
 )
 
-mapper(FakeTableClassicalyMapped, fake_table)
+reg = registry()
+reg.map_imperatively(FakeTableClassicalyMapped, fake_table)
 
 
 class FakeModel(object):
@@ -311,10 +312,16 @@ class TestPaginateQuery(test_base.BaseTestCase):
             'another_crit',
         ]
 
-        with mock.patch.object(self.model.user_id, 'isnot') as mock_isnot, \
-                mock.patch.object(self.model.user_id, 'is_') as mock_is_a, \
-                mock.patch.object(self.model.project_id, 'is_') as mock_is_b:
-            mock_isnot.return_value = 'asc_null_1'
+        with mock.patch.object(
+            self.model.user_id.comparator.expression, 'is_not'
+        ) as mock_is_not, \
+                mock.patch.object(
+                    self.model.user_id.comparator.expression, 'is_'
+                ) as mock_is_a, \
+                mock.patch.object(
+                    self.model.project_id.comparator.expression, 'is_'
+                ) as mock_is_b:
+            mock_is_not.return_value = 'asc_null_1'
             mock_is_a.side_effect = [
                 'desc_null_filter_1',
                 'desc_null_filter_2',
@@ -330,7 +337,7 @@ class TestPaginateQuery(test_base.BaseTestCase):
                                  sort_dirs=[
                                      'asc-nullslast', 'desc-nullsfirst'])
 
-            mock_isnot.assert_called_once_with(None)
+            mock_is_not.assert_called_once_with(None)
             mock_is_a.assert_has_calls([
                 mock.call(None),
                 mock.call(None),
@@ -384,11 +391,17 @@ class TestPaginateQuery(test_base.BaseTestCase):
         mock_and.return_value = 'some_crit'
         mock_or.side_effect = ['or_1', 'some_f']
 
-        with mock.patch.object(self.model.user_id, 'isnot') as mock_isnot, \
-                mock.patch.object(self.model.updated_at, 'is_') as mock_is_a, \
-                mock.patch.object(self.model.user_id, 'is_') as mock_is_b:
-
-            mock_isnot.return_value = 'asc_null_1'
+        with mock.patch.object(
+            self.model.user_id.comparator.expression, 'is_not'
+        ) as mock_is_not, \
+                mock.patch.object(
+                    self.model.updated_at.comparator.expression, 'is_'
+                ) as mock_is_a, \
+                mock.patch.object(
+                    self.model.user_id.comparator.expression, 'is_'
+                ) as mock_is_b:
+
+            mock_is_not.return_value = 'asc_null_1'
             mock_is_a.return_value = 'desc_null_1'
             mock_is_b.side_effect = ['asc_null_filter_1', 'asc_null_filter_2']
 
@@ -397,7 +410,7 @@ class TestPaginateQuery(test_base.BaseTestCase):
                                  marker=self.marker,
                                  sort_dirs=[
                                      'asc-nullslast', 'desc-nullsfirst'])
-            mock_isnot.assert_called_once_with(None)
+            mock_is_not.assert_called_once_with(None)
             mock_is_a.assert_called_once_with(None)
             mock_is_b.assert_has_calls([mock.call(None), mock.call(None)])
 
@@ -445,12 +458,20 @@ class TestPaginateQuery(test_base.BaseTestCase):
         ]
         self.query.filter.return_value = self.query
 
-        with mock.patch.object(self.model.user_id, 'isnot') as mock_isnot, \
-                mock.patch.object(self.model.updated_at, 'is_') as mock_is_a, \
-                mock.patch.object(self.model.user_id, 'is_') as mock_is_b, \
-                mock.patch.object(self.model.project_id, 'is_') as mock_is_c:
-
-            mock_isnot.return_value = 'asc_null_1'
+        with mock.patch.object(
+            self.model.user_id.comparator.expression, 'is_not'
+        ) as mock_is_not, \
+                mock.patch.object(
+                    self.model.updated_at.comparator.expression, 'is_'
+                ) as mock_is_a, \
+                mock.patch.object(
+                    self.model.user_id.comparator.expression, 'is_'
+                ) as mock_is_b, \
+                mock.patch.object(
+                    self.model.project_id.comparator.expression, 'is_'
+                ) as mock_is_c:
+
+            mock_is_not.return_value = 'asc_null_1'
             mock_is_a.return_value = 'desc_null_1'
             mock_is_b.side_effect = ['asc_null_filter_1', 'asc_null_filter_2']
             mock_is_c.side_effect = ['desc_null_3', 'desc_null_filter_3']
@@ -461,7 +482,7 @@ class TestPaginateQuery(test_base.BaseTestCase):
                                  sort_dirs=['asc-nullslast', 'desc-nullsfirst',
                                             'desc-nullsfirst'])
 
-            mock_isnot.assert_called_once_with(None)
+            mock_is_not.assert_called_once_with(None)
             mock_is_a.assert_called_once_with(None)
             mock_is_b.assert_has_calls([mock.call(None), mock.call(None)])
             mock_is_c.assert_has_calls([mock.call(None), mock.call(None)])
@@ -932,12 +953,12 @@ class TestConnectionUtils(test_base.BaseTestCase):
     def setUp(self):
         super(TestConnectionUtils, self).setUp()
 
-        self.full_credentials = {'backend': 'postgresql',
+        self.full_credentials = {'backend': 'postgresql+psycopg2',
                                  'database': 'test',
                                  'user': 'dude',
                                  'passwd': 'pass'}
 
-        self.connect_string = 'postgresql://dude:pass@localhost/test'
+        self.connect_string = 'postgresql+psycopg2://dude:pass@localhost/test'
 
         # NOTE(rpodolyaka): mock the dialect parts, so that we don't depend
         # on psycopg2 (or any other DBAPI implementation) in these tests
@@ -945,8 +966,20 @@ class TestConnectionUtils(test_base.BaseTestCase):
         @classmethod
         def fake_dbapi(cls):
             return mock.MagicMock()
-        patch_dbapi = mock.patch.object(psycopg2.PGDialect_psycopg2, 'dbapi',
-                                        new=fake_dbapi)
+
+        class OurDialect(psycopg2.PGDialect_psycopg2):
+            def dbapi(self):
+                return fake_dbapi
+
+            def import_dbapi(self):
+                return fake_dbapi
+
+        patch_dbapi = mock.patch.object(
+            psycopg2,
+            "PGDialect_psycopg2",
+            new=OurDialect,
+        )
+
         patch_dbapi.start()
         self.addCleanup(patch_dbapi.stop)
 
@@ -965,7 +998,7 @@ class TestConnectionUtils(test_base.BaseTestCase):
                 self.connect_string)
 
             self.assertIsInstance(eng, sqlalchemy.engine.base.Engine)
-            self.assertEqual(self.connect_string, str(eng.url))
+            self.assertEqual(utils.make_url(self.connect_string), eng.url)
 
             mock_connect.assert_called_once()
             fake_connection.close.assert_called_once()
@@ -982,10 +1015,10 @@ class TestConnectionUtils(test_base.BaseTestCase):
                 provision.Backend._ensure_backend_available,
                 self.connect_string)
             self.assertEqual(
-                "Backend 'postgresql' is unavailable: "
+                "Backend 'postgresql+psycopg2' is unavailable: "
                 "Could not connect", str(exc))
             self.assertEqual(
-                "The postgresql backend is unavailable: %s" % err,
+                "The postgresql+psycopg2 backend is unavailable: %s" % err,
                 log.output.strip())
 
     def test_ensure_backend_available_no_dbapi_raises(self):
@@ -1003,10 +1036,10 @@ class TestConnectionUtils(test_base.BaseTestCase):
                 utils.make_url(self.connect_string))
 
             self.assertEqual(
-                "Backend 'postgresql' is unavailable: "
+                "Backend 'postgresql+psycopg2' is unavailable: "
                 "No DBAPI installed", str(exc))
             self.assertEqual(
-                "The postgresql backend is unavailable: Can't import "
+                "The postgresql+psycopg2 backend is unavailable: Can't import "
                 "DBAPI module foobar", log.output.strip())
 
     def test_get_db_connection_info(self):
diff --git a/releasenotes/notes/sqlalchemy-20-0a193a01c70f805a.yaml b/releasenotes/notes/sqlalchemy-20-0a193a01c70f805a.yaml
new file mode 100644
index 0000000..b2c8d62
--- /dev/null
+++ b/releasenotes/notes/sqlalchemy-20-0a193a01c70f805a.yaml
@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    oslo.db now supports SQLAlchemy 2.0.
+  - |
+    A new ``oslo_db.compat`` module has been added. This provides a number of
+    shims for handling differences between SQLAlchemy 1.x and 2.x.
+upgrade:
+  - |
+    The ability to create engine facades that used autocommit, first deprecated
+    in 12.1.0, has now been removed. This is not supported in SQLAlchemy 2.x.