Spring data jpa @Version注解及自定义数据库乐观锁实现

客官°小女子只卖身不卖艺 2022-05-18 09:28 328阅读 0赞

在数据库并发操作时，为了保证数据的正确性，经常要对数据加锁，加锁有两种方式：悲观锁、乐观锁

悲观锁：把所需要的数据全部加锁，不允许其他事务对数据做修改

update xxx where xxxx for update

乐观锁：对数据进行版本校验，如果版本不一致，则操作数据失败

update xxx,version+1  where xxxx and version=x

在jpa中，@Version注解，可以实现乐观锁功能

实体类Account，version属性上加@Version注解

package com.xhx.springboot.entity;
    
    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.Version;
    
    /**
     * @author xuhaixing
     * @date 2018/4/28 10:29
     */
    @Entity
    public class Account {
        @Id
        private int id;
        private String name;
        private Double money;
        @Version
        private int version;
    
    
        public int getVersion() {
            return version;
        }
    
        public void setVersion(int version) {
            this.version = version;
        }
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Double getMoney() {
            return money;
        }
    
        public void setMoney(Double money) {
            this.money = money;
        }
    }

在更新数据时，需要用jpa自己实现的save方法

<S extends T> S save(S var1);
    
        <S extends T> Iterable<S> saveAll(Iterable<S> var1);

如果是自己写的update方法，下面这样，是不生效的

@Repository
    public interface AccountDao extends JpaRepository<Account, Integer> {
    
    
        @Modifying
        @Query("update Account set name=:name, money=:money where id=:id")
        int updateAccount(@Param("id") int id,@Param("name") String name, @Param("money") double money);
    
    }

数据库数据如下：

![70][]

我们更新id是10的数据，数据库中版本是0，我们设置版本1

Account account = new Account();
            account.setId(10);
            account.setName("eeee");
            account.setMoney(7999.0);
            account.setVersion(1);
    
            accountController.update(account);

报如下错误：

org.springframework.orm.ObjectOptimisticLockingFailureException: Object of class [com.xhx.springboot.entity.Account] with identifier [10]: optimistic locking failed; nested exception is org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.xhx.springboot.entity.Account#10]
    
    	at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:298)
    	at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:225)
    	at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:527)

把版本号改成0，再更新，数据库中执行如下语句，更新成功

![70 1][]

再看数据库，版本号+1了

![70 2][]

自己实现可以这样：

@Modifying
    @Query("update Account set name=:name, money=:money,version=:version+1 where id=:id and version=:version")
    int updateAccountByVersion(@Param("id") int id,@Param("name") String name, @Param("money") double money,@Param("version") int version);

service中加判断，抛异常，这样就自己通过数据库实现了乐观锁

@Transactional(rollbackFor = Exception.class)
        public int updateAccountByVersion(Account account){
            int i =accountDao.updateAccountByVersion(account.getId(),account.getName(),account.getMoney(),account.getVersion());
            if(i==0){
                throw new ObjectOptimisticLockingFailureException("更新account失败",new Exception());
            }
            return i;
        }

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[70]: /images/20220518/9efb6ada26f14409bfff9522ede829ab.png
[70 1]: /images/20220518/6c9637472cc54008b6bbf21db2db7bd2.png
[70 2]: /images/20220518/629a0e7052d84d299b0a3d70aa77000b.png
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