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# interfaces.py
# 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
"""Interfaces and abstract types."""
class PoolListener(object):
"""Hooks into the lifecycle of connections in a ``Pool``.
All of the standard connection [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.
"""
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 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.
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.
"""
def execute(self, conn, execute, clauseelement, *multiparams, **params):
""""""
return execute(clauseelement, *multiparams, **params)
def cursor_execute(self, execute, cursor, statement, parameters, context, executemany):
""""""
return execute(cursor, statement, parameters, context)
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