The class MapperExtension has some methods, and before_insert, before_update, ... all have a parameter connection.
def before_insert(self, mapper, connection, instance):
I've read the documents of MapperExtension, but found nothing about this connection. What is it? And how to use it?
Denis Otkidach
It's an instance of Connection class. Recent versions of SQLAlchemy distribution have examples directory, see examples/nested_sets/nested_sets.py to get an idea on how to use it in mapper extension.
来源：https://stackoverflow.com/questions/3646773/what-is-the-connection-parameter-of-mapperextension-in-sqlalchemy