mapping an interface?

sagimann · **Joined:** Sun Jun 11, 2006 10:41 am **Posts:** 164

Hi all,
I have the following object model:

Code:

public interface Component {
   void start();
   void stop();
}

public class MyComp implements Component {
...
}

public class Server {
   Component comp;
   void setComponent(Component c) { comp = c; }
// component is a part of the server, but may vary in implementation
}

Let's also assume all components are in a single table (COMPONENT) with a discriminator column (CLASS).

How do I create mapping files for this object model? Hibernate forces me to provide an 'id' in the Component.hbm.xml file, but obviously, I do not want to expose any id-handling in this interface... I'd rather keep it private in the MyComp implementation.

Hibernate version:
3.1

Mapping documents:

Code between sessionFactory.openSession() and session.close():
Server s1 = new Server();
s1.setComponent(new MyComp());

Full stack trace of any exception that occurs:

Name and version of the database you are using:
HSQLDB 1.8.0.4

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

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tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Read up on the table per class hierarchy polymorphism implementation strategy. Specify only classes in your mapping files, not interfaces. As you are implementing table per class hierarchy, obviously all implementations have the same ID and discriminator, at least: make a ComponentImpl class that includes these, and have all your component implementations extend that.

You can also specify abstract="true" on your top-level mapping, and specify the id element in all concrete mappings. That's a waste of effort, IMO.