Spring-Hibernate持久化不会导致插入

Question

我正在尝试实现一个简单的DAO.我有道:

@Repository("iUserDao")
@Transactional(readOnly = true)
public class UserDao implements IUserDao {
    private EntityManager entityManager;

    @PersistenceContext
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    @Override
    public User getById(int id) {
        return entityManager.find(User.class, id);
    }

    @Override
    public boolean save(User user) {
        entityManager.persist(user);
        entityManager.flush();
        return true;
    }

    @Override
    public boolean update(User user) {
        entityManager.merge(user);
        entityManager.flush();
        return true;
    }

    @Override
    public boolean delete(User user) {
        user = entityManager.getReference(User.class, user.getId());
        if (user == null)
            return false;
        entityManager.remove(user);
        entityManager.flush();
        return true;
    }

一个实体:

@Entity
@Table(name = "users")
public class User {
    private int id;
    private Date creationDate;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int getId() {
        return id;
    }

    public User() {
    }

    public User(Date creationDate) {
        this.creationDate = creationDate;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Date getCreationDate() {
        return creationDate;
    }

    public void setCreationDate(Date creationDate) {
        this.creationDate = creationDate;
    }
}

这是appContext.xml:`

<bean id="entityManagerFactory"
      class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
      p:dataSource-ref="dataSource" p:jpaVendorAdapter-ref="jpaAdapter"
      p:persistenceUnitName="test">
    <property name="loadTimeWeaver">
        <bean
                class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver"/>
    </property>
</bean>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager"
      p:entityManagerFactory-ref="entityManagerFactory"/>
<bean id="jpaAdapter"
      class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"
      p:database="MYSQL" p:showSql="true"/>

<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/>
<tx:annotation-driven/>`

除非我flush()之后调用persist()或merge()插入未执行.这是为什么？如果我删除@Transactional然后我得到关于刷新的"没有事务正在进行"的错误,但如果删除flush没有插入到数据库中.

Answer 1

它以这种方式工作,因为您将事务标记为只读@Transactional(readOnly = true).

正如您所看到的,它不会使您的事务实际上是只读的,因为您仍然可以通过flush()手动调用来保持更改.但是,它会在事务结束时禁用自动刷新,因此如果没有手动刷新,则不会保留更改.

您需要readOnly从类级别注释中删除,或者在具有方法级注释的非只读方法上覆盖它:

@Override
@Transactional(readOnly = false)
public boolean save(User user) { ... }

另请注意,事务划分通常应用于服务层方法,而不是DAO方法.特别是,在编写DAO方法时,您实际上不知道哪些事务应该是只读的,哪些不是.此信息仅在设计服务层时可用,如本例中所示:

public class UserService {
    @Autowired UserDAO dao;

    @Transactional(readOnly = true) 
    public User getUserById(int id) {
        return dao.getById(id); // getById() can participate in effectively read-only transaction
    }

    @Transactional
    public void changeUserName(int id, String newName) {
        User u = dao.getById(id); // Or not
        u.setName(newName); // Change will be flushed at the end of transaction
    }
}