Hello.
I have a naive system that links dict-like objects to mapped classes
so that rows can be saved to the db. It doesn't know anything about
mapped class instances, so many-to-many relationships are [currently]
saved by a class mapped to the swing table itself; for example, it's
the equivalent of :
client_role = Role(role_name="client")
acme = Organization(
organization_name="Acme")
acme_is_a_client = OrganizationRoles(
organization_id = acme.id,
role_id = client_role.id)
The deletion process iters through from child to parent according to
foreign keys and performs :
session.delete(acme_is_a_client)
session.delete(acme)
session.delete(client_role)
However, if somewhere in the app
"Organization.query().join('roles').select()" was performed, then
deleting acme will fail because it would have been deleted
automatically by session.delete(acme_is_a_client). Specifically, I
get a ConcurrentModificationError saying the deleted row count was 0.
Given the limitation of this approach and not trying to depend on the
configuration of ondelete/passive_deletes, is it possible to simply
detect whether or not acme or client_role has been deleted in the
session before deleting? That is, something more like :
if not object_was_deleted(session, acme_is_a_client):
session.delete(acme_is_a_client)
if not object_was_deleted(session, acme):
# this should not be executed
session.delete(acme)
if not object_was_deleted(session, client_role):
# nor this
session.delete(client_role)
The implementation below seems to detect deletions of the same object
but *not* the above scenario where the objects deleted were children :
def object_was_deleted(session, obj):
from sqlalchemy.orm.mapper import object_mapper
for c in [obj] + list(object_mapper(obj).cascade_iterator(
'delete', obj)):
if c in session.uow.deleted:
return True
elif not session.uow._is_valid(c):
return True
return False
Is there a way to detect deleted children? Thanks for reading and let
me know if you need a more concrete example
-Kumar
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