[TM4J-users] Hibernate and Locators

[Thomas M. <th...@sn...>]

Hi,

I want to look up all topics that have a certain subject indicator. While
this works without problems with the in-memory backend, there seems to be no
elegant solution for the Hibernate backend:

// using Hibernate provider...
LocatorFactory lf         = provider.getLocatorFactory();
Locator        psiSynonym = lf.createLocator( "URI", PSI_SYNONYM );
TopicMap       tm;
// ...
Collection c = tm.getUtils().getMembersOfType( topic, psiSynonym );

The last line causes a ClassCastException with the Hibernate backend...
because the Hibernate implementation of getMembersOfType() uses a cast to
URILocatorImpl on the Locator object:

  LocatorDataObject ldo = (LocatorDataObject) sess.load(
                          LocatorDataObject.class,
          ====>           ((URILocatorImpl) subjectOrIndicator)
                          .getPersistenceId());

But createLocator() returns instances of TransientURILocatorImpl, so this
cannot work.

I've found a workaround by using an implementation specific call to create
suitable Locator instances:

if (lf instanceof org.tm4j.topicmap.hibernate.LocatorFactoryImpl) {
  psiSynonym = ((org.tm4j.topicmap.hibernate.LocatorFactoryImpl)lf)
               .createPersistentLocator( "URI", PSI_SYNONYM );
}
else {
  psiSynonym = lf.createLocator( "URI", PSI_SYNONYM );
}

This works (and TM4J uses the same "trick" in its
getSubClasses/getSuperClasses methods), but it does not seem elegant to me
(it relies on the implementation instead of a public interface).

Is there a better solution that uses only public API and does not depend on
a certain implementation?

bye, Thomas