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
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.
Oleg.
--
Oleg Broytmann http://phd.pp.ru/ [email protected]
Programmers don't die, they just GOSUB without RETURN.
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