我有一个基本的SpringBoot 2.0.4.RELEASE应用程序，使用Spring初始化程序、JPA、嵌入式Tomcat、Thymeleaf模板引擎，并将其打包为一个可执行的JAR文件。
我有这个方法：

@Transactional
    public User createUser(User user, Set<UserRole> userRoles) {

        User localUser = userRepository.findByEmail(user.getEmail());

        if (localUser != null) {
            LOG.info("User with username {} and email {} already exist. Nothing will be done. ",
                    user.getUsername(), user.getEmail());
        } else {

            String encryptedPassword = passwordEncoder.encode(user.getPassword());
            user.setPassword(encryptedPassword);

            for (UserRole ur : userRoles) {

                LOG.info("Saving role " + ur);

                roleRepository.save(ur.getRole());
            }

            user.getUserRoles().addAll(userRoles);

            localUser = userRepository.save(user);

        }

        return localUser;
    }

但当我创建用户时：

User user = new User();

        Set<UserRole> userRoles = new HashSet<>();
        userRoles.add(new UserRole(user, new Role(RolesEnum.ADMIN)));
        userService.createUser(user, userRoles);

我得到这个错误：

object references an unsaved transient instance - save the transient instance before flushing : com.tdk.backend.persistence.domain.backend.UserRole.role -> com.tdk.backend.persistence.domain.backend.Role