对于托管实体调用save是一个坏主意，因为Hibernate使用脏检查机制来帮助我们避免这种冗余调用。
关键点：
- Hibernate对于托管实体会触发UPDATE语句，无需显式调用save()方法
- 在幕后，进行冗余save()调用意味着性能损失（见这里）
@SpringBootApplication
public class RedundantSaveApplication {
private static final Logger logger = Logger.getLogger(RedundantSaveApplication.class.getName());
@Autowired
private UserService userService;
public static void main(String[] args) {
SpringApplication.run(RedundantSaveApplication.class, args);
}
@Bean
public ApplicationRunner init() {
return args -> {
userService.updateUserNameViaRedundantSave();
userService.updateUserNameRecommended();
};
}
}
@Repository
public interface UserRepository extends JpaRepository<User, Long> {
}
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@Service
public class UserService {
@Autowired
private UserRepository userRepository;
@Transactional
public void updateUserNameViaRedundantSave(){
User user = userRepository.findById(1L).get();
user.setName("Hulyo G");
userRepository.save(user); //冗余
}
@Transactional
public void updateUserNameRecommended(){
User user = userRepository.findById(1L).get();
user.setName("Magic J");
}
}
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