fully support isolation_level parameter in base dialect

Generalized the :paramref:`_sa.create_engine.isolation_level` parameter to
the base dialect so that it is no longer dependent on individual dialects
to be present. This parameter sets up the "isolation level" setting to
occur for all new database connections as soon as they are created by the
connection pool, where the value then stays set without being reset on
every checkin.

The :paramref:`_sa.create_engine.isolation_level` parameter is essentially
equivalent in functionality to using the
:paramref:`_engine.Engine.execution_options.isolation_level` parameter via
:meth:`_engine.Engine.execution_options` for an engine-wide setting. The
difference is in that the former setting assigns the isolation level just
once when a connection is created, the latter sets and resets the given
level on each connection checkout.

Fixes: #6342
Change-Id: Id81d6b1c1a94371d901ada728a610696e09e9741

1 files changed, 2 insertions, 7 deletions

diff --git a/lib/sqlalchemy/dialects/oracle/base.py b/lib/sqlalchemy/dialects/oracle/base.py
index 229a54b95..9846a65bd 100644
--- a/lib/sqlalchemy/dialects/oracle/base.py
+++ b/lib/sqlalchemy/dialects/oracle/base.py
@@ -1573,10 +1573,8 @@ class OracleDialect(default.DefaultDialect):
             # use the default
             return None
 
-    _isolation_lookup = ["READ COMMITTED", "SERIALIZABLE"]
-
-    def get_isolation_level(self, connection):
-        raise NotImplementedError("implemented by cx_Oracle dialect")
+    def get_isolation_level_values(self, dbapi_conn):
+        return ["READ COMMITTED", "SERIALIZABLE"]
 
     def get_default_isolation_level(self, dbapi_conn):
         try:
@@ -1586,9 +1584,6 @@ class OracleDialect(default.DefaultDialect):
         except:
             return "READ COMMITTED"
 
-    def set_isolation_level(self, connection, level):
-        raise NotImplementedError("implemented by cx_Oracle dialect")
-
     def has_table(self, connection, table_name, schema=None):
         self._ensure_has_table_connection(connection)