events.py 文件源码

def before_attach(self, session, instance):
        """Execute before an instance is attached to a session.

        This is called before an add, delete or merge causes
        the object to be part of the session.

        .. versionadded:: 0.8.  Note that :meth:`~.SessionEvents.after_attach`
           now fires off after the item is part of the session.
           :meth:`.before_attach` is provided for those cases where
           the item should not yet be part of the session state.

        .. seealso::

            :meth:`~.SessionEvents.after_attach`

            :ref:`session_lifecycle_events`

        """