SQLAlchemy cascades deletes to collections associated with objects that are present in the Session. Not every database supports cascading of foreign keys. I didn't introduce this concept in my last email, but if you configure foreign key level cascades, and your application is only to be used on a cascade-supporting backend, you also can configure passive_deletes=True so that SQLA won't go through the effort of loading in collections to be deleted that aren't already present.
http://www.sqlalchemy.org/docs/orm/session.html#deleting http://www.sqlalchemy.org/docs/orm/collections.html#using-passive-deletes On Feb 25, 2011, at 11:09 AM, Eric Ongerth wrote: > Wouldn't he need to configure the "ondelete" cascade for even > "session.delete(session.query(User).get('testname'))" to work that > way? > > I know why the cascade is necessary for session.query(User).delete() > to also delete the associated IP instances. But I don't quite get why > it's not necessary for that other method of deleting the user to > delete the associated IPs. > > > On Feb 25, 7:17 am, Michael Bayer <mike...@zzzcomputing.com> wrote: >> On Feb 25, 2011, at 7:31 AM, Chris Withers wrote: >> >> >> >>> Hi All, >> >>> I have the following models: >> >>> class IP(Base): >>> __tablename__ = 'ip' >>> username = Column(String(50), >>> ForeignKey('user.username'), >>> primary_key=True) >>> ip = Column(String(15), primary_key=True, index=True) >> >>> class User(Base): >>> __tablename__ = 'user' >>> username = Column(String(50), primary_key=True) >>> ips = relation("IP", >>> order_by="IP.ip", >>> backref="user", >>> cascade="all") >> >>> If I delete a user as follows: >> >>> session.delete(session.query(User).get('testname')) >> >>> ...then the IPs associated with 'testname' get deleted. >> >>> However, if I do: >> >>> session.query(User).delete() >> >>> ..they do not. >> >>> Why is that? >>> How do I get them both to work? >> >> you would need to configure "ON DELETE CASCADE" on the foreign key. >> ForeignKey() offers the "ondelete" option for this. >> >> >> >>> cheers, >> >>> Chris >> >>> -- >>> Simplistix - Content Management, Batch Processing & Python Consulting >>> -http://www.simplistix.co.uk >> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To post to this group, send email to sqlalchemy@googlegroups.com. >>> To unsubscribe from this group, send email to >>> sqlalchemy+unsubscr...@googlegroups.com. >>> For more options, visit this group >>> athttp://groups.google.com/group/sqlalchemy?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalchemy@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
