我正在尝试实现一个简单的DAO.
我有道：
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/>`
除非我在persist()或merge()之后调用flush(),否则insert不会执行.
这是为什么？
如果我删除@Transactional然后我在刷新时遇到“没有事务正在进行中”的错误,但是如果删除了flush没有插入到DB中.
解决方法
它以这种方式工作,因为您使用@Transactional(readOnly = true)将事务标记为只读.
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手动调用flush()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.
您需要从类级别注释中删除readOnly,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
}
}