use the "passive_updates=True, passive_deletes='all'" flags. These
are described at
http://www.sqlalchemy.org/docs/05/sqlalchemy_orm.html#docstrings_sqlalchemy.orm_modfunc_relation
.
On Dec 5, 2008, at 11:42 AM, James Brady wrote:
> Hi all,
> I'm trying to get deletes and updates cascaded down from a parent
> object to the child objects (connected by ForeignKey).
>
> It all seems pretty simple in the docs, but I can't get it to work!
> I'm using MySQL with the InnoDB engine, and have played with all the
> variation of the onupdate, ondelete and cascade arguments I can
> think of.
>
> The problem is that immediately before the DELETE command is sent to
> MySQL, there are UPDATE commands nulling out the foreign key
> references of the child objects, so MySQL doesn't trigger it's ON
> DELETE CASCADE action, and for some reason cascade="all, delete-
> orphan" doesn't clean up the children with NULL FKs.
>
> Here's a simplified model:
> users_table = Table('tg_user', metadata,
> Column('user_id', Integer, primary_key=True),
> Column('created', DateTime, default=datetime.now),
> mysql_engine='InnoDB',
> )
>
> hat_table = Table('hat', metadata,
> Column('id', Integer, primary_key=True),
> Column('name', Unicode(100)),
> Column('user_id', Integer, ForeignKey('tg_user.user_id'),
> onupdate='CASCADE', ondelete='CASCADE'),
> mysql_engine='InnoDB',
> )
>
> class User(object):
> pass
>
> class Hat(object):
> pass
>
> mapper(User, users_table)
>
> mapper(Hat, hat_table,
> properties = {
> 'user': relation(User, backref="hats", cascade="all, delete,
> delete-orphan"),
> }
> )
>
> And the log from SA when I do a User.delete:
> BEGIN
> UPDATE hat SET user_id=%s WHERE hat.id = %s
> [None, 1L]
> DELETE FROM tg_user WHERE tg_user.user_id = %s
> [1L]
> COMMIT
>
> Any help would be much appreciated!
>
> James
>
> >
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