我在纠结这个奇怪的错误：CrudRepository的findById()方法返回Optional.empty，除非之前在使用mysql时调用了findAll()。
例如
使用者

@Entity
public class User {

    @Id
    @GeneratedValue
    private UUID id;

    public UUID getId() {
        return id;
    }

}

UserRepository

public interface UserRepository extends CrudRepository<User, UUID> { }

用户服务

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    @Transactional
    public UUID create() {
        final User user = new User();
        userRepository.save(user);
        return user.getId();
    }

    @Transactional
    public User find(@PathVariable UUID userId) {
        // userRepository.findAll(); TODO without this functin call, Optinoal.empty is returned by the repo
        return userRepository.findById(userId).orElseThrow(() -> new IllegalArgumentException(String.format("missing user:%s", userId)));
    }
}

UserApp

@SpringBootApplication
public class UserApp {

    private static final Logger LOG = LoggerFactory.getLogger(UserApp.class);

    @Autowired
    private UserService userService;

    @EventListener
    public void onApplicationEvent(ContextRefreshedEvent event) {
        final UUID userId = userService.create();
        final User user = userService.find(userId);
        LOG.info("found user: {}", user.getId());
    }

    public static void main(String[] args) {
        SpringApplication.run(UserApp.class, args);
    }

}

application.properties

spring.datasource.url=jdbc:mysql://localhost:3306/db_test
spring.datasource.username=springuser
spring.datasource.password=ThePassword

spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.show-sql=true
spring.jpa.database=mysql

为什么findAll()方法调用会改变findById()的结果？
编辑：使用findAll的Hibernate日志：

Hibernate: drop table if exists user
Hibernate: create table user (id binary(255) not null, primary key (id)) engine=MyISAM
Hibernate: insert into user (id) values (?)
Hibernate: select user0_.id as id1_0_ from user user0_

无：

Hibernate: drop table if exists user
Hibernate: create table user (id binary(255) not null, primary key (id)) engine=MyISAM
Hibernate: insert into user (id) values (?)
Hibernate: select user0_.id as id1_0_0_ from user user0_ where user0_.id=?