Oh, of course - thanks Michael!
On Feb 7, 1:51 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
> cascade="all" includes "delete" cascade. any Hat objects attached to
> User will be deleted when the User is deleted. To resolve, leave
> the "cascade" argument out. it defaults to "save-update, merge" which
> is enough for most use cases.
>
> On Feb 6, 2009, at 11:05 PM, James wrote:
>
>
>
> > Hi, I'm trying to set up a model where child objects are allowed to
> > not have parents. At present, I can't get SA to leave the children
> > intact, despite having ondelete="SET NULL" and no "delete-orphan"s.
>
> > This is with SA 0.4.3.
>
> > To demonstrate my confusion, can someone explain why this code deletes
> > all my hats:
>
> > import sys, time
> > from datetime import datetime
> > from sqlalchemy import Table, Column, ForeignKey, MetaData,
> > create_engine
> > from sqlalchemy.orm import relation, sessionmaker, mapper, backref
> > from sqlalchemy import String, Unicode, Integer, DateTime
>
> > metadata=MetaData()
> > engine = create_engine("sqlite:///:memory:")
>
> > users_table = Table('tg_user', metadata,
> > Column('user_id', Integer, primary_key=True),
> > )
>
> > hat_table = Table('hat', metadata,
> > Column('id', Integer, primary_key=True),
> > Column('user_id', Integer, ForeignKey('tg_user.user_id',
> > ondelete='SET NULL')),
> > )
>
> > metadata.create_all(engine)
>
> > class User(object):
> > pass
>
> > class Hat(object):
> > pass
>
> > mapper(User, users_table)
>
> > mapper(Hat, hat_table,
> > properties = {
> > 'user': relation(User, backref=backref("hats",
> > cascade="all")),
> > }
> > )
>
> > Session = sessionmaker(bind=engine, autoflush=False,
> > transactional=True)
> > session = Session()
>
> > me = User()
> > me.hats.extend([Hat(), Hat(), Hat()])
> > session.save(me)
> > session.flush()
>
> > print session.query(Hat).count(), "hats"
> > session.delete(me)
> > session.flush()
> > print session.query(Hat).count(), "hats"
>
> > Thank you!
> > James
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