- New features added to support engine/pool plugins with advanced

functionality.   Added a new "soft invalidate" feature to the
connection pool at the level of the checked out connection wrapper
as well as the :class:`._ConnectionRecord`.  This works similarly
to a modern pool invalidation in that connections aren't actively
closed, but are recycled only on next checkout; this is essentially
a per-connection version of that feature.  A new event
:class:`.PoolEvents.soft_invalidate` is added to complement it.
fixes #3379

- Added new flag
:attr:`.ExceptionContext.invalidate_pool_on_disconnect`.
Allows an error handler within :meth:`.ConnectionEvents.handle_error`
to maintain a "disconnect" condition, but to handle calling invalidate
on individual connections in a specific manner within the event.

- Added new event :class:`.DialectEvents.do_connect`, which allows
interception / replacement of when the :meth:`.Dialect.connect`
hook is called to create a DBAPI connection.  Also added
dialect plugin hooks :meth:`.Dialect.get_dialect_cls` and
:meth:`.Dialect.engine_created` which allow external plugins to
add events to existing dialects using entry points.
fixes #3355

1 files changed, 14 insertions, 2 deletions

diff --git a/lib/sqlalchemy/engine/strategies.py b/lib/sqlalchemy/engine/strategies.py
index 1fd105d67..a802e5d90 100644
--- a/lib/sqlalchemy/engine/strategies.py
+++ b/lib/sqlalchemy/engine/strategies.py
@@ -48,7 +48,8 @@ class DefaultEngineStrategy(EngineStrategy):
         # create url.URL object
         u = url.make_url(name_or_url)
 
-        dialect_cls = u.get_dialect()
+        entrypoint = u.get_dialect()
+        dialect_cls = entrypoint.get_dialect_cls(u)
 
         if kwargs.pop('_coerce_config', False):
             def pop_kwarg(key, default=None):
@@ -81,11 +82,18 @@ class DefaultEngineStrategy(EngineStrategy):
         # assemble connection arguments
         (cargs, cparams) = dialect.create_connect_args(u)
         cparams.update(pop_kwarg('connect_args', {}))
+        cargs = list(cargs)  # allow mutability
 
         # look for existing pool or create
         pool = pop_kwarg('pool', None)
         if pool is None:
-            def connect():
+            def connect(connection_record=None):
+                if dialect._has_events:
+                    for fn in dialect.dispatch.do_connect:
+                        connection = fn(
+                            dialect, connection_record, cargs, cparams)
+                        if connection is not None:
+                            return connection
                 return dialect.connect(*cargs, **cparams)
 
             creator = pop_kwarg('creator', connect)
@@ -157,6 +165,10 @@ class DefaultEngineStrategy(EngineStrategy):
                 dialect.initialize(c)
             event.listen(pool, 'first_connect', first_connect, once=True)
 
+        dialect_cls.engine_created(engine)
+        if entrypoint is not dialect_cls:
+            entrypoint.engine_created(engine)
+
         return engine