I have a scenario in a system which I've tried to simplify as best as
I can. We have a table of (lets call them) artefacts, artefacts can be
accessed by any number of security roles and security roles can access
any number of artefacts. As such, we have 3 tables in the database -
one describing artefacts, one describing roles and a many-to-many
association table linking artefact ID to Role ID.
Domain wise, we have two classes - one for a role and one for an
artefact. the artefact class has an IList property that returns a list
of roles that can access it. (Roles however do not offer a property to
get artefacts that can be accessed).
As such, the nhibernate mapping for artefact contains the following;
<bag name="AccessRoles" table="ArtefactAccess" order-by="RoleID"
lazy="true" access="field.camelcase-underscore" optimistic-
lock="false">
<key column="ArtefactID"/>
<many-to-many class="Role" column="RoleID"/>
</bag>
This all works fine and if I delete an artefact, the association table
is cleaned up appropriately and all references between the removed
artefact and roles are removed (the role isn't deleted though,
correctly - as we don't want orphans deleted).
The problem is - how to delete a role and have it clear up the
association table automatically. If I presently try to delete a role,
I get a reference constraint as there are still entries in the
association table for the role. The only way to successfully delete a
role is to query for all artefacts that link to that role, remove the
role from the artefact's role collection, update the artefacts and
then delete the role - not very efficient or nice, especially when in
the un-simplified system, roles can be associated with any number of
other tables/objects.
I’ve tried adding a protected IList bag to role that links up to
artefact’s (even though I don’t want this in my domain model) and set
this as the inverse relationship (inverse=”true” on the bag) but this
doesn’t solve the problem.
I need to be able to hint to NHibernate that I want this association
table cleared whenever I delete a role - is this possible, and if so -
how do I do it?
Thanks for any help.
