improve error raise for dialect/pool events w/ async engine

Fixed issues where a descriptive error message was not raised for some
classes of event listening with an async engine, which should instead be a
sync engine instance.

Change-Id: I00b9f4fe9373ef5fd5464fac10651cc4024f648e

1 files changed, 10 insertions, 2 deletions

diff --git a/lib/sqlalchemy/ext/asyncio/events.py b/lib/sqlalchemy/ext/asyncio/events.py
index a059b93e6..c5d5e0126 100644
--- a/lib/sqlalchemy/ext/asyncio/events.py
+++ b/lib/sqlalchemy/ext/asyncio/events.py
@@ -16,21 +16,29 @@ class AsyncConnectionEvents(engine_event.ConnectionEvents):
     _dispatch_target = AsyncConnectable
 
     @classmethod
-    def _listen(cls, event_key, retval=False):
+    def _no_async_engine_events(cls):
         raise NotImplementedError(
             "asynchronous events are not implemented at this time.  Apply "
             "synchronous listeners to the AsyncEngine.sync_engine or "
             "AsyncConnection.sync_connection attributes."
         )
 
+    @classmethod
+    def _listen(cls, event_key, retval=False):
+        cls._no_async_engine_events()
+
 
 class AsyncSessionEvents(orm_event.SessionEvents):
     _target_class_doc = "SomeSession"
     _dispatch_target = AsyncSession
 
     @classmethod
-    def _listen(cls, event_key, retval=False):
+    def _no_async_engine_events(cls):
         raise NotImplementedError(
             "asynchronous events are not implemented at this time.  Apply "
             "synchronous listeners to the AsyncSession.sync_session."
         )
+
+    @classmethod
+    def _listen(cls, event_key, retval=False):
+        cls._no_async_engine_events()