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interfaces.py
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# sqlalchemy/interfaces.py # Copyright (C) 2007-2021 the SQLAlchemy authors and contributors # <see AUTHORS file> # Copyright (C) 2007 Jason Kirtland jek@discorporate.us # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Deprecated core event interfaces. .. deprecated:: 0.7 As of SQLAlchemy 0.7, the new event system described in :ref:`event_toplevel` replaces the extension/proxy/listener system, providing a consistent interface to all events without the need for subclassing. """ from . import event from . import util class PoolListener(object): """Hooks into the lifecycle of connections in a :class:`_pool.Pool`. .. deprecated:: 0.7 :class:`.PoolListener` is deprecated and will be removed in a future release. Please refer to :func:`.event.listen` in conjunction with the :class:`_events.PoolEvents` listener interface. 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 :class:`~sqlalchemy.pool.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. """ @classmethod def _adapt_listener(cls, self, listener): """Adapt a :class:`.PoolListener` to individual :class:`event.Dispatch` events. """ methods = ["connect", "first_connect", "checkout", "checkin"] listener = util.as_interface(listener, methods=methods) for meth in methods: me_meth = getattr(PoolListener, meth) ls_meth = getattr(listener, meth, None) if ls_meth is not None and not util.methods_equivalent( me_meth, ls_meth ): util.warn_deprecated( "PoolListener.%s is deprecated. The " "PoolListener class will be removed in a future " "release. Please transition to the @event interface, " "using @event.listens_for(Engine, '%s')." % (meth, meth) ) if hasattr(listener, "connect"): event.listen(self, "connect", listener.connect) if hasattr(listener, "first_connect"): event.listen(self, "first_connect", listener.first_connect) if hasattr(listener, "checkout"): event.listen(self, "checkout", listener.checkout) if hasattr(listener, "checkin"): event.listen(self, "checkin", listener.checkin) def connect(self, 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 """ def first_connect(self, 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 """ def checkout(self, 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. """ def checkin(self, 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 """ class ConnectionProxy(object): """Allows interception of statement execution by Connections. .. deprecated:: 0.7 :class:`.ConnectionProxy` is deprecated and will be removed in a future release. Please refer to :func:`.event.listen` in conjunction with the :class:`_events.ConnectionEvents` listener interface. Either or both of the ``execute()`` and ``cursor_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 :class:`~sqlalchemy.engine.Engine` via the ``proxy`` argument:: e = create_engine('someurl://', proxy=MyProxy()) """ @classmethod def _adapt_listener(cls, self, listener): methods = [ "execute", "cursor_execute", "begin", "rollback", "commit", "savepoint", "rollback_savepoint", "release_savepoint", "begin_twophase", "prepare_twophase", "rollback_twophase", "commit_twophase", ] for meth in methods: me_meth = getattr(ConnectionProxy, meth) ls_meth = getattr(listener, meth) if not util.methods_equivalent(me_meth, ls_meth): util.warn_deprecated( "ConnectionProxy.%s is deprecated. The " "ConnectionProxy class will be removed in a future " "release. Please transition to the @event interface, " "using @event.listens_for(Engine, '%s')." % (meth, meth) ) def adapt_execute(conn, clauseelement, multiparams, params): def execute_wrapper(clauseelement, *multiparams, **params): return clauseelement, multiparams, params return listener.execute( conn, execute_wrapper, clauseelement, *multiparams, **params ) event.listen(self, "before_execute", adapt_execute) def adapt_cursor_execute( conn, cursor, statement, parameters, context, executemany ): def execute_wrapper(cursor, statement, parameters, context): return statement, parameters return listener.cursor_execute( execute_wrapper, cursor, statement, parameters, context, executemany, ) event.listen(self, "before_cursor_execute", adapt_cursor_execute) def do_nothing_callback(*arg, **kw): pass def adapt_listener(fn): def go(conn, *arg, **kw): fn(conn, do_nothing_callback, *arg, **kw) return util.update_wrapper(go, fn) event.listen(self, "begin", adapt_listener(listener.begin)) event.listen(self, "rollback", adapt_listener(listener.rollback)) event.listen(self, "commit", adapt_listener(listener.commit)) event.listen(self, "savepoint", adapt_listener(listener.savepoint)) event.listen( self, "rollback_savepoint", adapt_listener(listener.rollback_savepoint), ) event.listen( self, "release_savepoint", adapt_listener(listener.release_savepoint), ) event.listen( self, "begin_twophase", adapt_listener(listener.begin_twophase) ) event.listen( self, "prepare_twophase", adapt_listener(listener.prepare_twophase) ) event.listen( self, "rollback_twophase", adapt_listener(listener.rollback_twophase), ) event.listen( self, "commit_twophase", adapt_listener(listener.commit_twophase) ) def execute(self, conn, execute, clauseelement, *multiparams, **params): """Intercept high level execute() events.""" return execute(clauseelement, *multiparams, **params) def cursor_execute( self, execute, cursor, statement, parameters, context, executemany ): """Intercept low-level cursor execute() events.""" return execute(cursor, statement, parameters, context) def begin(self, conn, begin): """Intercept begin() events.""" return begin() def rollback(self, conn, rollback): """Intercept rollback() events.""" return rollback() def commit(self, conn, commit): """Intercept commit() events.""" return commit() def savepoint(self, conn, savepoint, name=None): """Intercept savepoint() events.""" return savepoint(name=name) def rollback_savepoint(self, conn, rollback_savepoint, name, context): """Intercept rollback_savepoint() events.""" return rollback_savepoint(name, context) def release_savepoint(self, conn, release_savepoint, name, context): """Intercept release_savepoint() events.""" return release_savepoint(name, context) def begin_twophase(self, conn, begin_twophase, xid): """Intercept begin_twophase() events.""" return begin_twophase(xid) def prepare_twophase(self, conn, prepare_twophase, xid): """Intercept prepare_twophase() events.""" return prepare_twophase(xid) def rollback_twophase(self, conn, rollback_twophase, xid, is_prepared): """Intercept rollback_twophase() events.""" return rollback_twophase(xid, is_prepared) def commit_twophase(self, conn, commit_twophase, xid, is_prepared): """Intercept commit_twophase() events.""" return commit_twophase(xid, is_prepared)