问题
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?
回答1:
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