@Entity
@Table(name = "users", uniqueConstraints = @UniqueConstraint(columnNames = { "username" }))
public class User extends BaseEntity {
    @Column(name = "username", length = 50, nullable = false)
    private String username;

    @Column(name = "password", length = 50, nullable = false)
    private String password;

    @Column(name = "enabled", columnDefinition = "TINYINT")
    private boolean enabled;

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
    private Set<Authority> authorities;

@Entity
@Table(name = "authorities", uniqueConstraints = @UniqueConstraint(columnNames= {"username", "authority"}))
public class Authority extends BaseEntity {
   
    @ManyToOne(optional = false)
    @JoinColumn(name = "username", referencedColumnName = "username", updatable = true)
    private User user;

    @Column(name = "authority", length = 50, nullable = false)
    private String authority;

   public static void main(String[] args) {
       
       EntityManagerFactory emf = new HibernateUtils().getEMF();
        EntityManager entityManager = (EntityManager) emf.createEntityManager();
        entityManager.getTransaction().begin();
       
        User u = new User();
        u.setUsername("asd");
        u.setPassword("asd");
       
       
        save(u, entityManager);
       
        User u1 = entityManager.find(User.class, 1l);
        u1.setUsername("asda");
       
        save(u1, entityManager);
       
        HibernateUtils.commit(entityManager);
       
    }

    private static void save(User entity, EntityManager entityManager) {
        Set<Authority> authorities = entity.getAuthorities();
        System.out.println(authorities);
        if (null != authorities) {
            entity.setAuthorities(null);
            for (Authority authority : authorities) {
                entityManager.remove(authority);
            }           
        }
       
        Authority auth = new Authority();
        auth.setUser(entity);
        boolean isAdmin = true;
        auth.setAuthority(isAdmin ? "ROLE_ADMIN" : "ROLE_USER");
        entity.addAuthority(auth);
       
        entity.setEnabled(true);       

        if (entity.isNew()) {
            entityManager.persist(entity);
        } else {
            entityManager.merge(entity);
        }
    }