Persist subclass as superclass using Hibernate

Question

I have a subclass and a superclass. However, only the fields of the superclass are needed to be persist.

session.saveOrUpdate((Superclass) subclass);

If I do the above, I will get the following exception.

org.hibernate.MappingException: Unknown entity: test.Superclass
    at org.hibernate.impl.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:628)
    at org.hibernate.impl.SessionImpl.getEntityPersister(SessionImpl.java:1366)
    at org.hibernate.engine.ForeignKeys.isTransient(ForeignKeys.java:203)
    at org.hibernate.event.def.AbstractSaveEventListener.getEntityState(AbstractSaveEventListener.java:535)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:103)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
    at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:535)
    at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:527)
    at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:523)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:342)
    at $Proxy54.saveOrUpdate(Unknown Source)

How can I persist a subclass as a superclass? I do not prefer creating a superclass instance and then passing the values from the subclass instance. Because, it is easy to forget updating the logic if extra fields are added to superclass in the future.

Answer 1

What you try to achieve will cause you a lot of problems. Just imagine what happens if you load the data again. Which class is Hibernate supposed to use? The superclass? Or one of the subclasses? Which one?

I suggest to map the superclass directly and then use the delegate pattern to implement the extended functionality (basically turning your superclass in a data object which gets passed to "worker" instances).