SQLAlchemy 1.1 Documentation
Deprecated Event Interfaces¶
This section describes the class-based core event interface introduced in SQLAlchemy 0.5. The ORM analogue is described at Deprecated ORM Event Interfaces.
Deprecated since version 0.7: The new event system described in Events replaces the extension/proxy/listener system, providing a consistent interface to all events without the need for subclassing.
Execution, Connection and Cursor Events¶
- class
sqlalchemy.interfaces.
ConnectionProxy
¶ Allows interception of statement execution by Connections.
Note
ConnectionProxy
is deprecated. Please refer toConnectionEvents
.Either or both of the
execute()
andcursor_execute()
may be implemented to intercept compiled statement and cursor level executions, e.g.:class MyProxy(ConnectionProxy): def execute(self, conn, execute, clauseelement, *multiparams, **params): print "compiled statement:", clauseelement return execute(clauseelement, *multiparams, **params) def cursor_execute(self, execute, cursor, statement, parameters, context, executemany): print "raw statement:", statement return execute(cursor, statement, parameters, context)
The
execute
argument is a function that will fulfill the default execution behavior for the operation. The signature illustrated in the example should be used.The proxy is installed into an
Engine
via theproxy
argument:e = create_engine('someurl://', proxy=MyProxy())
-
begin
(conn, begin)¶ Intercept begin() events.
-
begin_twophase
(conn, begin_twophase, xid)¶ Intercept begin_twophase() events.
-
commit
(conn, commit)¶ Intercept commit() events.
-
commit_twophase
(conn, commit_twophase, xid, is_prepared)¶ Intercept commit_twophase() events.
-
cursor_execute
(execute, cursor, statement, parameters, context, executemany)¶ Intercept low-level cursor execute() events.
-
execute
(conn, execute, clauseelement, *multiparams, **params)¶ Intercept high level execute() events.
-
prepare_twophase
(conn, prepare_twophase, xid)¶ Intercept prepare_twophase() events.
-
release_savepoint
(conn, release_savepoint, name, context)¶ Intercept release_savepoint() events.
-
rollback
(conn, rollback)¶ Intercept rollback() events.
-
rollback_savepoint
(conn, rollback_savepoint, name, context)¶ Intercept rollback_savepoint() events.
-
rollback_twophase
(conn, rollback_twophase, xid, is_prepared)¶ Intercept rollback_twophase() events.
-
savepoint
(conn, savepoint, name=None)¶ Intercept savepoint() events.
-
Connection Pool Events¶
- class
sqlalchemy.interfaces.
PoolListener
¶ Hooks into the lifecycle of connections in a
Pool
.Note
PoolListener
is deprecated. Please refer toPoolEvents
.Usage:
class MyListener(PoolListener): def connect(self, dbapi_con, con_record): '''perform connect operations''' # etc. # create a new pool with a listener p = QueuePool(..., listeners=[MyListener()]) # add a listener after the fact p.add_listener(MyListener()) # usage with create_engine() e = create_engine("url://", listeners=[MyListener()])
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 ofcheckout
events, and either n or n - 1checkin
events. (If aConnection
is detached from its pool via thedetach()
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 orClauseElement
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 internalPool
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. ThePool
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.-
checkin
(dbapi_con, con_record)¶ 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.)- dbapi_con
- A raw DB-API connection
- con_record
- The
_ConnectionRecord
that persistently manages the connection
-
checkout
(dbapi_con, con_record, con_proxy)¶ Called when a connection is retrieved from the Pool.
- dbapi_con
- A raw DB-API connection
- con_record
- The
_ConnectionRecord
that persistently manages the connection - con_proxy
- The
_ConnectionFairy
which manages the connection for the span of the current checkout.
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.
-
connect
(dbapi_con, con_record)¶ Called once for each new DB-API connection or Pool’s
creator()
.- dbapi_con
- A newly connected raw DB-API connection (not a SQLAlchemy
Connection
wrapper). - con_record
- The
_ConnectionRecord
that persistently manages the connection
-
first_connect
(dbapi_con, con_record)¶ Called exactly once for the first DB-API connection.
- dbapi_con
- A newly connected raw DB-API connection (not a SQLAlchemy
Connection
wrapper). - con_record
- The
_ConnectionRecord
that persistently manages the connection
-