Hi Oleg,
On Wednesday 12 August 2009 10:06:30 Oleg Broytmann wrote:
> On Tue, Aug 11, 2009 at 07:40:12AM +0200, Tom Coetser wrote:
> > class Member(SQLObject):
> > name = StringCol(alternateID=True)
> > roles = SQLRelatedJoin('Role', intermediateTable='member_role',
> > createRelatedTable=False)
> >
> > class Role(SQLObject):
> > name = StringCol(alternateID=True)
> > members = SQLRelatedJoin('Member', intermediateTable='member_role',
> > createRelatedTable=False)
> >
> > class MemberRole(SQLObject):
> > member = ForeignKey('Member', notNull=True, cascade=False)
> > role = ForeignKey('Role', notNull=True, cascade=False)
> >
> > When I call destroySelf() on a member though, I would like to **not**
> > have that member deleted if it still has any roles assigned to it. I
> > tried setting the cascade=False option in the intermediate table, but
> > this does not help because it looks like the base destroySelf() method
> > automatically deletes any RelatedJoins.
>
> First thing I can guess your are using a backend that doesn't support
> CASCADE (SQLite?) With SQLite, you can CREATE a TRIGGER to prevent deletion
No, I am using Postgres after burning my fingers during the testing stages
with exactly this using SQLite.
> from the intermediate table, but you have to do it yourself.
> .destroySelf() actually doesn't rely on the backend support for CASCADE;
> instead it uses it itself, but not on the RelatedJoin's intermediate table
> even if the table is declared explicitly. The simplest way I see is to
> override .destroySelf:
>
> class Member(SQLObject):
> name = StringCol(alternateID=True)
> roles = SQLRelatedJoin('Role', intermediateTable='member_role',
> createRelatedTable=False)
>
> def destroySelf(self):
> if list(self.roles): # or self.roles.count()
> raise RuntimeError('Cannot delete a member (%s) that has roles'
> % self.id)
> super(Member, self).destroySelf()
>
> class Role(SQLObject):
> name = StringCol(alternateID=True)
> members = SQLRelatedJoin('Member', intermediateTable='member_role',
> createRelatedTable=False)
>
> def destroySelf(self):
> try:
> self.members[0]
> except IndexError:
> super(Role, self).destroySelf()
> else:
> raise RuntimeError('Cannot delete a role (%s) that has members'
> % self.id)
>
> I showed three different ways to check for RelatedJoin. This of course
> only works with .destroySelf - other means will happily delete rows.
Thanks. Yes, I did end up overriding .destroySelf() and that seems to work
fine. The other methods of deleting records are handled directly by the
backend via the cascade=False on the ForeignKeys on the intermediate table.
The only awkward part is that exception handling is a bit weird due to
different exceptions being raised for essentially the same reason but using
different delete methods. But for now I can live with this :-)
Thanks for the help.
Cheers,
Tom
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