Toplink mapping for one-to-many object inheritance

Question

Hi
I currently have a Person object, extended by two specialist classes, PremisesLicenceHolder and PersonalLicenceHolder. I have mapped this in Toplink and it works fine saving a person into the specialist tables using the primary key person_id.
However, a single Person may be extended any number of times by either one or both of the two specialist types. So, a Person may be a PremisesLicenceHolder many times over for different premises and licences, and also a PersonalLicenceHolder several times over.
Is it possible to map this object model in Toplink avoiding duplicate person_id primary keys in the specialist tables?
Thanks

Answer 1

Hi,
I am happy that my object model fits the problem domain. The Person and Organisation objects contain base information and have the primary keys person_id and organisation_id. It is important that there is no duplication of person and organisation records, no matter how many times they are saved in different roles.
There are two types of licenceholder in the problem domain, and the ILicenceHolder interface defines information and methods that are common to both. The PersonalLicenceHolder object represents one of these types of licenceholder, and is always a person, so this class extends Person and implements ILicenceHolder.
The additional information and methods that are required by the second type of licenceholder are defined in the interface IPremisesLicenceHolder, which extends ILicenceHolder. Premises licence holders can either be people or organisations, so I have two objects to represent these - PremisesLicenceHolderPerson which implements IPremisesLicenceHolder and extends Person, and PremisesLicenceHolderOrganisation which implements IPremisesLicenceHolder and extends Organisation.
The model is further complicated by the fact that any single Person may be both a PersonalLicenceHolder and a PremisesLicenceHolderPerson, and may be so several times over. In this case, the same basic Person information needs to be linked to several different sets of licenceholder information. In the same way, any single Organisation may be a PremisesLicenceHolderOrganisation several times over.
Sorry this is complicated!
My initial idea for the schemas is to have Person and Organisation tables containing the basic information with the primary keys person_id and organisation_id. The Person table would have a one-to-many relationship with both the PersonalLicenceHolder table (pk: personalLicenceHolder_id, fk: person_id), and the PremisesLicenceHolderPerson table (pk: premisesLicenceHolderPerson_id, fk: person_id). There would also be a one-to-many relationship between the Organisation table and the PremisesLicenceHolderOrganisation table (pk: premisesLicenceHolderOrganisation_id, fk: organisation_id).
I am flexible as to the design of my schema though, as I am happy to adopt any that will facilitate the Toplink Mapping.
Thanks for your help with this.