JPA使用中應注意的地方

• ​​寫在前面​​
• ​​一、事務處理​​
• ​​二、儲存和批量儲存​​
• ​​三、SQL日志列印問題​​

寫在前面

一、事務處理

@Transactional，這個注解，想要關聯事務處理，要特别注意異常處理

二、儲存和批量儲存

關于JPA中save,saveAndFlush和saveAll的差別，

@Transactional
  public <S extends T> S save(S entity) {
    if (entityInformation.isNew(entity)) {
      em.persist(entity);
      return entity;
    } else {
      return em.merge(entity);
    }
  }      

@Transactional
  public <S extends T> S saveAndFlush(S entity) {
    S result = save(entity);
    flush();
    return result;
  }      

@Transactional
  public <S extends T> List<S> saveAll(Iterable<S> entities) {
    Assert.notNull(entities, "The given Iterable of entities not be null!");
    List<S> result = new ArrayList<S>();
    for (S entity : entities) {
      result.add(save(entity));
    }
    return result;
  }      

// 測試，耗時約 130-170 s
 @GetMapping("/batch-add")
    public ResultBean batchAdd() {

        LocalDateTime start = LocalDateTime.now();
        for (int i = 60000; i < 61000; i++) {
            UserInfo u = new UserInfo();
            u.setUserName("name" + i);
            u.setUserCode("code" + i);
            userRepository.save(u);
        }
        LocalDateTime end = LocalDateTime.now();
        return ResultBean.ok(ChronoUnit.SECONDS.between(start,end));
    }
//  測試，耗時約 1 s
    @GetMapping("/batch-all")
    public ResultBean batchAllAdd() {

        ArrayList<UserInfo> list = Lists.newArrayList();
        LocalDateTime start = LocalDateTime.now();
        for (int i = 61000; i < 62000; i++) {
            UserInfo u = new UserInfo();
            u.setUserName("name" + i);
            u.setUserCode("code" + i);
            list.add(u);
        }
        userRepository.saveAll(list);
        LocalDateTime end = LocalDateTime.now();
        return ResultBean.ok(ChronoUnit.SECONDS.between(start, end));
    }      

三、SQL日志列印問題