参考文献

JPA自动更新问题

环境以及版本
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SpringBoot 2.2.2.RELEASE
MySQL      8.0.24
示例1
  • 描述: 不加@Transactional注解,两次查询,第一次查询修改实体的某个值
  • 结果: 两次查询的结果一致
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@GetMapping("/test3")
 public void test3() {
     Optional<TestJpa> byId = testDAO.findById(36);
     if (byId.isPresent()) {
         TestJpa test = byId.get();
         // id=36, x=0, y=71, z=53
         log.info("test: {}", test);
         test.setX(123);
     }
     TestJpa test2 = testDAO.findById(36).get();
     log.info("test2: {}", test2);
 }

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示例2
  • 描述: 相对示例1,多了个@Transactional
  • 结果: 两次查询的结果不一致,第一次查询后修改的值,在方法结束前自动更新了数据库
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@Transactional
@GetMapping("/test4")
public void test4() {
    Optional<TestJpa> byId = testDAO.findById(36);
    if (byId.isPresent()) {
        TestJpa test = byId.get();
        // id=36, x=0, y=71, z=53
        log.info("test: {}", test);
        test.setX(123);
    }
    TestJpa test2 = testDAO.findById(36).get();
    log.info("test2: {}", test2);
}

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分析

  • Hibernate对象生命周期

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  • 第一查询到的数据test为持久态,修改X后还是持久态,当第二次查询相同的记录的时候,是直接从持久态上下文获取的.

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  • 最后在方法结束前提交事务前会做下列操作

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    Execute all SQL (and second-level cache updates) in a special order so that foreign-key constraints cannot be violated:
    Inserts, in the order they were performed
    Updates
    Deletion of collection elements
    Insertion of collection elements
    Deletes, in the order they were performed
    Params:
    session – The session being flushed

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示例3
  • 描述: 相对示例2,多了entityManager.unwrap(org.hibernate.Session.class).evict(test);
  • 结果和示例1相似,两次查询结果一致
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@Transactional
@GetMapping("/test5")
public void test5() {
    Optional<TestJpa> byId = testDAO.findById(36);
    if (byId.isPresent()) {
        TestJpa test = byId.get();
        // id=36, x=0, y=71, z=53
        log.info("test: {}", test);
        test.setX(123);
        entityManager.unwrap(org.hibernate.Session.class).evict(test);
    }
    TestJpa test2 = testDAO.findById(36).get();
    log.info("test2: {}", test2);
}

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