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Spring JPA 事务只读与自动持久化

JPA Hibernate 框架中的实体entity有三种状态，transient(瞬时状态)，persistent(持久化状态)以及detached(离线状态)自动持久化，本文主要是讨论持久化状态的一些细节问题。

如果一个实体entity通过query语句查出来后，调用实体相关的setXXX方法，有可能会被待久化到db中，也有可以不会，总体来说，关键点取决于setXXX方法所处的函数是否有事务（Session）包裹着，但到生产环境中，会有比较多的复杂情况，下面我们以声明式事务的实现方式来探讨，编程式事务主要就是手工对session和transaction的管理，与之类似，亦可借鉴。

1、单一业务，自动提交场景（主方法test有事务）：

@Service
public class FunctionService {

    private Logger logger = LoggerFactory.getLogger(FunctionService.class);
    @Autowired
    private TUserServcie tUserServcie;
    @Autowired
    private TAddressServcie tAddressServcie;
    
    //测试方法
    @Transactional()
    public void test(String name){
        TUser user = tUserServcie.findByName(name);
        logger.info("test before age:"+user.getAge());
        user.setAge(user.getAge()+1);
    }
}

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2、单一业务，不会自动提交场景（主方法test不含事务事务或为read-only）：

@Service
public class FunctionService {

    private Logger logger = LoggerFactory.getLogger(FunctionService.class);
    @Autowired
    private TUserServcie tUserServcie;
    @Autowired
    private TAddressServcie tAddressServcie;
    //测试方法
    //@Transactional(readOnly = true)
    public void test(String name){
        TUser user = tUserServcie.findByName(name);
        logger.info("test before age:"+user.getAge());
        user.setAge(user.getAge()+1);
    }
}

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3、复合业务，不会自动提交（test无事务或read-only且countAllNotTrans无事务或read-only）

@Service
public class FunctionService {
    private Logger logger = LoggerFactory.getLogger(FunctionService.class);
    @Autowired
    private TUserServcie tUserServcie;
    @Autowired
    private TAddressServcie tAddressServcie;
    
    //测试方法
    //@Transactional(readOnly = true)
    public void test(String name){
        TUser user = tUserServcie.findByName(name);
        logger.info("test before age:"+user.getAge());
        user.setAge(user.getAge()+1);
        tAddressServcie.countAll();
    }
}

@Service
public class TAddressServcie {
    @Autowired
    private TAddressRepo tAddressRepo;
    
    //@Transactional(readOnly = true)
    public int countAll (){
        return tAddressRepo.countAll();
    }
}

public interface TAddressRepo extends JpaRepository<TAddress, Integer> {
    @Query(value ="SELECT count(*) FROM TAddress")
    int countAll();
}
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4、特别注意！！！复合业务，会自动提交（test无事务，countAll有事务）

@Service
public class FunctionService {
    private Logger logger = LoggerFactory.getLogger(FunctionService.class);
    @Autowired
    private TUserServcie tUserServcie;
    @Autowired
    private TAddressServcie tAddressServcie;
    //测试方法
    public void test(String name){
        TUser user = tUserServcie.findByName(name);
        logger.info("test before age:"+user.getAge());
        user.setAge(user.getAge()+1);
        tAddressServcie.countAll();
    }
}

@Service
public class TAddressServcie {
    @Autowired
    private TAddressRepo tAddressRepo;
    
    @Transactional()
    public int countAll (){
        return tAddressRepo.countAll();
    }
}

public interface TAddressRepo extends JpaRepository<TAddress, Integer> {
    @Query(value ="SELECT count(*) FROM TAddress")
    int countAll();
}
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原文 https://juejin.im/post/5cff5fb15188251346598eeb

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