@Entity
@Table(name="ADMIN_OBJECT")
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class DBObject{
    @Column(length = 255, nullable = false)
    private String name;
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Long id;
    @Column(length=1024)
    private String description;
    @Column(nullable = false)
    @Version
    private Long version;
   
   
    public DBObject(){
    }
   
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public  Long getId(){
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public Long getVersion() {
        return version;
    }
    public void setVersion(Long version) {
        this.version = version;
    } 
}

@Entity
@Table(name="ADMIN_USER")
public class User extends DBObject{
    @ManyToOne
    @JoinColumn(name="groupID", nullable = false)
    private Group group;
   
    public User(){
        super();
    }


    public void setGroup(Group group) {
        this.group = group;
    }




    public Group getGroup() {
        return group;
    }   
   
}

@Entity
@Table(name="ADMIN_GROUP")
public class Group extends DBObject{
    @OneToMany(mappedBy="group")
    private List<User> userList;
   
   
    public Group(){
        super();
    }
        public List<User> getUserList() {
        return userList;
    }


    public void setUserList(List<User> userList) {
        this.userList = userList;
    }
   
}

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
        session.beginTransaction();
       
        session.save(org);
        session.flush();
       
        Group g = new Group();
        g.setName("Group 1");
        session.save(g);
       
       
       
        User user = new User();
        user.setGroup(g);
        user.setName("User1");
        session.save(user);
       
       
        User user2 = new User();
        user2.setGroup(g);
        user.setName("User2");       
        session.save(user2);
       

        session.flush();
        List<Group> groupList = session.createQuery("from Group as group").list();
        for(Group group: groupList){
            System.out.println(group);
        }