Extend JPA entity to add attributes and logic

问题

I need to know if it's possible to add some attributes and behaviours to some POJO JPA entity (using hibernate provider) by extending it, and then to make entityManager to return extended objects instead of just pojo entitys, like the following examples:

POJO JPA Entity Class

@Entity
@Table("test")
public class Test implements Serializable {
}

Extended Class

public class ExtendedTest extends Test {
...
}

Fetching Extended Class's objects

List<ExtendedTest> extendedList = entityManager.createNamedQuery("ExtendedTest.findByFoo").setParameter("foo", "bar").getResultList();

The other possible way i'm assessing is extending funcionality with a composite entity and delegating all setters and getters, but this could mean a lot of work with huge tables:

public class ExtendedTest2 {
    private Test test;

    public ExtendedTest2(Test test) {
        this.test = test;
    }

    public getFoo() {
        return test.getFoo();
    }

    public getBar() {
        return test.getBar();
    } 

    ...
}

Any suggestions will be very appreciated.

回答1:

Using @Inheritance

@Entity
@Table(name="TEST")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
public class Test {
    ...
}

@Entity
public class ExtendedTest 
    extends Test {
    ...
}  

or @MappedSuperclass

@MappedSuperclass
public class Test {
    ...
}

@Entity
public class ExtendedTest 
    extends Test {
    ...
}

来源：https://stackoverflow.com/questions/12570251/extend-jpa-entity-to-add-attributes-and-logic