On Nov 8, 2010, at 11:02 AM, Mene wrote:
> Hi all,
> I have some 'child' tables which inherit from the same 'master' table,
> now I'd like to delete some entries from all tables. The 'where'-part
> comes solely from the master table.
> I have decided to use Concrete Table Inheritance since I don't need
> the inheritance at points other than deleting, but I expect the tables
> to have a lot of entries and at the moment I don't know how many child
> tables I will have in the future. Also the delete process won't occur
> often.
>
> Each table has a compound primary key of user and room.
> I use version 0.4.8 (and I can't change this)
>
> I need a delete statement that deletes according to user_id and the
> length of the room identifier.
> Also master is only an abstract class, so I don't need to have a table
> in my database (AFAIK).
There's only two choices here, you can either load the objects with the ORM and
individually pass them to session.delete(), or you can emit DELETE statements
against the tables directly using SQL expressions or strings. The SQL
expression would be along the lines of
Session.execute(master.delete().where(...)).
>
> master = Table('master', metadata,
> Column('user_id', Integer, ForeignKey('user.user_id',
> ondelete='CASCADE'), primary_key=True),
> Column('room', Unicode(16), ForeignKey('room.id'),
> primary_key=True)
> )
>
> child1 = Table('child1', metadata,
> Column('user_id', Integer, ForeignKey('user.user_id',
> ondelete='CASCADE'), primary_key=True),
> Column('room', Unicode(16), ForeignKey('room.id'),
> primary_key=True),
> Column('child1_data', Unicode(16))
> )
>
> child2 = Table('child2', metadata,
> Column('user_id', Integer, ForeignKey('user.user_id',
> ondelete='CASCADE'), primary_key=True),
> Column('room', Unicode(16), ForeignKey('room.id'),
> primary_key=True),
> Column('child2_data', Unicode(16))
> )
>
> join = polymorphic_union({
> 'master': master,
> 'child1': child1,
> 'child2': child2
> }, 'type', 'pjoin')
>
> master_mapper = mapper(Master, master, with_polymorphic=('*',
> vote_join), \
> polymorphic_on=vote_join.c.type, polymorphic_identity='vote_data')
>
> child1_mapper = mapper(Child1, child1, inherits=master, \
> concrete=True, polymorphic_identity='child1')
>
> child2_mapper = mapper(Child2, child2, inherits=master, \
> concrete=True, polymorphic_identity='child2')
>
> Thanks for your time,
> Mene
>
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