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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