net.java.ao
Annotation Type Polymorphic

@Retention(value=RUNTIME)
@Target(value=TYPE)
public @interface Polymorphic

Tags a given entity type as polymorphically abstract. This means that the given type will not peer to any table, but rather represent a polymorphic supertype to other entities (entities which extend the given interface). Unlike conventional inheritence, which also causes the supertype to not peer to a table, polymorphic type inheritence allows instances of the subtype to be stored in the database into fields which are "typed" in ActiveObjects as the supertype. All of this is really much simpler than it sounds:

public interface Person extends Entity {
     public Computer getComputer();
     public void setComputer(Computer computer);
 }
 
 @Polymorphic
 public interface Computer extends Entity {
     public float getSpeed();
     public void setSpeed(float speed);
 }
 
 public interface Mac extends Computer {}
 public interface PC extends Computer {}

In this case, Computer does not correspond with any table in the database. Likewise, Person has no foreign keys for the corresponding field to getComputer(). When an entity type is polymorphic, its subtypes can be used polymorphically as they are in Person. This is essentially the conceptual analog of an abstract class when mapped into the database.

Author:

Daniel Spiewak