Yes, I definitely want to emit a DELETE statement. The Problem is that
calling master.delete() only gives an delete statement for the master
table. However, I need n querys: DELETE child1... , DELETE child2 and
so on.
On 8 Nov., 20:31, Michael Bayer <mike...@zzzcomputing.com> wrote:
> 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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