Persisting interfaces using JDO/Datanucleus
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class TclRequest implements Comparable<TclRequest> {
    @PrimaryKey
    private String id;

    @Persistent(types = { DNSTestData.class, POP3TestData.class, PPPoETestData.class, RADIUSTestData.class }, defaultFetchGroup = "true")
    @Columns({ @Column(name = "dnstestdata_fk"), @Column(name = "pop3testdata_fk"), @Column(name = "pppoetestdata_fk"), @Column(name = "radiustestdata_fk") })
    private TestData testData;

    public String getId() {
        return id;
    }

    public TestData getTestData() {
        return testData;
    }

    public void setId(String id) {
        this.id = id;
    }

    public void setTestData(TestData testData) {
        this.testData = testData;
    }
}

@PersistenceCapable(detachable = "true")
    public interface TestData {
    @PrimaryKey
    public String getId();

    public void setId(String id);
}

@PersistenceCapable(detachable = "true")
public class RADIUSTestData implements TestData {
    @PrimaryKey
    private String id;
    private String password;
    private String username;

    public RADIUSTestData() {
    }

    public RADIUSTestData(String password, String username) {
        super();
        this.password = password;
        this.username = username;
    }

    @Override
    public String getId() {
        return id;
    }

    @Override
    public void setId(String id) {
        this.id = id;
    }
}

//'o' is the constructed TclRequest object.
PersistenceManager pm = null;
Transaction t = null;
try {
    pm = getPM();
    t = pm.currentTransaction();
    t.begin();
    pm.makePersistent(o);
    t.commit();
} catch (Exception e) {
    e.printStackTrace();
    if (t != null && t.isActive()) {
        t.rollback();
    }
} finally {
    closePM(pm);
}