不使用RepositoryRestResource插入重复项

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

    @Column(unique = true)
    private String username;

    // 其他字段和方法...
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    @Modifying
    @Transactional
    @Query(value = "INSERT INTO user (username) VALUES (:username) ON DUPLICATE KEY UPDATE username = :username", nativeQuery = true)
    void insertUser(@Param("username") String username);
}

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public void insertUser(String username) {
        try {
            userRepository.insertUser(username);
        } catch (DataIntegrityViolationException e) {
            // 处理插入重复项的情况
            throw new IllegalArgumentException("Username already exists.");
        }
    }
}