如何使用JPA删除连接表中的行

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String username;

    @ManyToMany
    @JoinTable(
        name = "user_role",
        joinColumns = @JoinColumn(name = "user_id"),
        inverseJoinColumns = @JoinColumn(name = "role_id")
    )
    private Set<Role> roles = new HashSet<>();

    // getters and setters
}

@Entity
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @ManyToMany(mappedBy = "roles")
    private Set<User> users = new HashSet<>();

    // getters and setters
}

public void deleteUserRole(Long userId, Long roleId) {
    EntityManager entityManager = entityManagerFactory.createEntityManager();
    EntityTransaction transaction = entityManager.getTransaction();

    try {
        transaction.begin();

        User user = entityManager.find(User.class, userId);
        Role role = entityManager.find(Role.class, roleId);

        if (user != null && role != null) {
            user.getRoles().remove(role);
            entityManager.merge(user);
        }

        transaction.commit();
    } catch (Exception e) {
        if (transaction != null && transaction.isActive()) {
            transaction.rollback();
        }
        e.printStackTrace();
    } finally {
        entityManager.close();
    }
}