JPA之@Version进行乐观锁并发更新

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在数据库并发操作时,为了保证数据的正确性,我们会做一些并发处理,主要就是加锁。在加锁的选择上,有几种方式,悲观锁,乐观锁。

悲观锁,简单的理解就是把需要的数据全部加锁,在事务提交之前,这些数据全部不可读取和修改。

乐观锁,使用对数据进行版本校验和比较,来对保证本次的更新时最新的,否则就失败。

悲观锁的做法:

select * from user where uid=1 for update;
update user  set name='bac'  where uid=1;

这样,uid为1的这行记录,就被锁住,在事务提交之前,他不可被其他事务读取和修改。

乐观锁的做法:

select uid,name,version from user where uid=1;

假设本次查询version=1,在更新操作时,

update user set name='abc', version=version+1 where uid=1 and version=1

这样,当其他事务在本次事务提交之前更新了,version就会+1,就不是刚才查询到的1,本次update 就失败。

在JPA中,我们可以使用@Version在某个字段上进行乐观锁控制。

@Entity
@Table(name = "data_version")
public class DataVersion extends BaseEntity {
    /**
     * 
     */
    private static final long serialVersionUID = 1830796806342370927L;
    private String name;
    private int age;
    @Version
    private Long version;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Long getVersion() {
        return version;
    }

    public void setVersion(Long version) {
        this.version = version;
    }

    @Override
    public String toString() {
        return "DataVersion [name=" + name + ", age=" + age + ", version=" + version + "]";
    }
}
@DataJpaTest
@RunWith(SpringRunner.class)
@ContextConfiguration(classes = Core.class)
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
public class JpaTest {
    @Autowired
    DataVersionJpaRepository jpa;

    @Test
    public void test() {
        DataVersion d = new DataVersion();
        d.setName("hello");
        d.setAge(27);
        d = jpa.saveAndFlush(d);
        Long id = d.getId();
        System.out.println(id);
        DataVersion d2 = jpa.findOne(id);
        d2.setAge(26);
        d2 = jpa.saveAndFlush(d2);
        System.out.println(d2);
    }
}
Hibernate: insert into data_version (enable, age, name, version) values (?, ?, ?, ?)
21
Hibernate: update data_version set enable=?, age=?, name=?, version=? where id=? and version=?
DataVersion [name=hello, age=26, version=1]

当乐观锁更新失败的时候,会抛出异常org.springframework.orm.ObjectOptimisticLockingFailureException

@RunWith(SpringRunner.class)
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
@SpringBootTest(classes = AccountsApplication.class)
public class JpaTest {
    @Autowired
    DataVersionJpaRepository jpa;

    @Test
    public void test() throws InterruptedException {
        DataVersion d = new DataVersion();
        d.setName("hello");
        d.setAge(27);
        d = jpa.saveAndFlush(d);
        Long id = d.getId();
        System.out.println(id);
        DataVersion d2 = jpa.findOne(id);
        d2.setAge(26);
        new Thread(new Runnable() {
            @Override
            public void run() {
                DataVersion d2 = jpa.findOne(id);
                d2.setAge(99);
                d2 = jpa.saveAndFlush(d2);
                System.out.println("th:" + d2);
            }
        }).start();
        Thread.sleep(5000);
        d2 = jpa.saveAndFlush(d2);
        System.out.println(d2);
        Thread.sleep(20000);
    }
}

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