Interfaces and abstract types.
Allows interception of statement execution by Connections.
Subclass ConnectionProxy, overriding either or both of execute() and cursor_execute() The default behavior is provided, which is to call the given executor function with the remaining arguments. The proxy is then connected to an engine via create_engine(url, proxy=MyProxy()) where MyProxy is the user-defined ConnectionProxy class.
Hooks into the lifecycle of connections in a Pool.
All of the standard connection Pool types can accept event listeners for key connection lifecycle events: creation, pool check-out and check-in. There are no events fired when a connection closes.
For any given DB-API connection, there will be one connect event, n number of checkout events, and either n or n - 1 checkin events. (If a Connection is detached from its pool via the detach() method, it won't be checked back in.)
These are low-level events for low-level objects: raw Python DB-API connections, without the conveniences of the SQLAlchemy Connection wrapper, Dialect services or ClauseElement execution. If you execute SQL through the connection, explicitly closing all cursors and other resources is recommended.
Events also receive a _ConnectionRecord, a long-lived internal Pool object that basically represents a "slot" in the connection pool. _ConnectionRecord objects have one public attribute of note: info, a dictionary whose contents are scoped to the lifetime of the DB-API connection managed by the record. You can use this shared storage area however you like.
There is no need to subclass PoolListener to handle events. Any class that implements one or more of these methods can be used as a pool listener. The Pool will inspect the methods provided by a listener object and add the listener to one or more internal event queues based on its capabilities. In terms of efficiency and function call overhead, you're much better off only providing implementations for the hooks you'll be using.
Called when a connection returns to the pool.
Note that the connection may be closed, and may be None if the connection has been invalidated. checkin will not be called for detached connections. (They do not return to the pool.)
Called when a connection is retrieved from the Pool.
If you raise an exc.DisconnectionError, the current connection will be disposed and a fresh connection retrieved. Processing of all checkout listeners will abort and restart using the new connection.
Called once for each new DB-API connection or Pool's creator().