如何在sqlalchemy中管理此提交/回退模式

从我的工作代码（会话注册表包装器的一种方法）来看，这是正确的。

它是这样使用的：

# dblink is an object that knows how to connect to the database
with dblink.CommittingSession() as session:
session.add(...)
# do anything else.
# at this point, session.commit() has been called.


要么：

try:
with dblink.CommittingSession() as session:
session.add(...)
except ...:
# at this point, session.rollback has been called.
log.error('We failed!')


实现：

from contextlib import contextmanager
class DbLink(object):
"""This class knows how to connect to the database."""
# ...
# Basically we wrap a sqlalchemy.orm.sessionmaker value here, in session_registry.
# You might want to create sessions differently.
@contextmanager
def CommittingSession(self, **kwargs):
"""Creates a session, commits at the end, rolls back on exception, removes.
Args:
**kwargs: optional; supplied to session_registry while asking
to construct a session (mostly for testing).
Yields:
a session object. The session will .commit() when a `with CommittingSession()`
statement terminates normally, or .rollback() on an exception.
"""
try:
session = self.session_registry(**kwargs) # this gives us a session.
# transaction has already begun here, so no explicit .begin().
yield session
except:
session.rollback()
raise
else:
session.commit()
finally:
# Note: close() unbinds model objects, but keeps the DB connection.
session.close()
self.session_registry.remove()