如何不在hibernate/springboot中获取@ManyToMany中的colletion？

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

public class UserRoleDTO {
    private Long userId;
    private Long roleId;
    // 其他需要的字段
    
    // 省略构造函数、getter和setter方法
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    @Query("SELECT new com.example.dto.UserRoleDTO(u.id, r.id) FROM User u JOIN u.roles r WHERE u.id = :userId")
    List<UserRoleDTO> findUserRoles(@Param("userId") Long userId);
}

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;
    
    public List<UserRoleDTO> getUserRoles(Long userId) {
        return userRepository.findUserRoles(userId);
    }
}