# -*- coding: utf-8 -*-
# Time-stamp: < tx.py (2016-02-14 01:05) >
# Copyright (C) 2009-2016 Martin Slouf <martin.slouf@sourceforge.net>
#
# This file is a part of Summer.
#
# Summer is free software; you can redistribute it and/or modify it under
# the terms of the GNU Lesser General Public License as published by the Free
# Software Foundation; either version 3 of the License, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""Module ``tx`` contains support for programmatic transaction management.
Declarative transaction management is defined in :py:mod:`summer.txaop`.
"""
import logging
from sqlalchemy.orm import Session
from .ex import AbstractMethodException
from .sf import SessionFactory
logger = logging.getLogger(__name__)
[docs]class TransactionCallback(object):
"""Callback object called from within a :py:class:`TransactionWrapper`."""
[docs] def txrun(self, session: Session, *args, **kwargs) -> object:
"""Executed inside transaction.
This is a callback method. It is discouraged to use the ``*args`` and
``**kwargs`` magic.
Args:
session (Session): *SQLAlchemy* session
Returns:
object: whatever you want to get returned from a transaction
"""
raise AbstractMethodException()
[docs]class TransactionWrapper(object):
"""Wraps the code it executes inside a transaction.
Caller provides a callback object (:py:class:`TransactionCallback`
instance) to be executed inside a transaction; it gets passed in the
current thread-bound *SQLAlchemy* session.
It participates in current transaction if there is one active or
creates a new one.
If exception is raised, transaction is rolled back.
"""
[docs] def __init__(self, session_factory: SessionFactory):
"""
Args:
session_factory (SessionFactory): session factory to be used
"""
self.session_factory = session_factory
[docs] def execute(self, callback: TransactionCallback, *args, **kwargs) -> object:
"""Runs the callback provided inside transaction.
Whatever other arguments are provided, they are passed to callback.
Args:
callback (TransactionCallback): callback to be executed
Returns:
object: whatever the callback returns
"""
session = self.session_factory.get_session()
logger.debug("tx begin with session %s", session)
active = session.active
try:
if active:
logger.debug("tx active, continue")
else:
session.begin()
logger.debug("tx not active, started")
sqlalchemy_session = session.sqlalchemy_session
result = callback.txrun(sqlalchemy_session, *args, **kwargs)
if active:
logger.debug("tx active, no commit")
else:
sqlalchemy_session.commit()
logger.debug("tx commit")
except Exception as ex:
session.rollback()
logger.exception("tx rollback")
raise ex
finally:
if active:
logger.debug("tx active, not closing")
else:
# TODO martin.slouf -- decide whether session can outlive
# the transaction -- can be handy and less resourceful
# session.close()
# logger.debug("tx closed")
pass
return result