Hibernate 4带有二级缓存:我的理解有什么不对？

Question

我已经开始使用Hibernate 4和二级缓存.根据文档,配置非常简单:

<property name="hibernate.cache.use_second_level_cache"  value="true"></property>
<property name="hibernate.cache.use_query_cache"  value="true"></property>
<property name="hibernate.cache.region.factory_class"  value="org.hibernate.cache.ehcache.EhCacheRegionFactory"></property>

根据我的理解,二级缓存应该消除对数据库的相同查询.我有非常简单的实体和非常简单的命名查询:

@Entity
@NamedQueries({
        @NamedQuery(name="SimplePerson.findByName", query="select p from SimplePerson p where p.name = :name"),
})

@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class SimplePerson {

    public static final String FIND_BY_NAME = "SimplePerson.findByName";

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String name;

    public SimplePerson() {

    }

    public SimplePerson(String name) {
        this.name = name;
    }



}

我运行命名查询4次,不幸的是我看到hibernate运行了4次.

EntityManagerFactory emf = Persistence.createEntityManagerFactory("test");      
EntityManager em = emf.createEntityManager();

Query query = em.createNamedQuery(SimplePerson.FIND_BY_NAME);
query.setParameter("name", "BOB");

List result = query.getResultList();
result = query.getResultList();
result = query.getResultList();
result = query.getResultList();

输出:

Hibernate: select simplepers0_.id as id0_, simplepers0_.name as name0_ from SimplePerson simplepers0_ where simplepers0_.name=?
Hibernate: select simplepers0_.id as id0_, simplepers0_.name as name0_ from SimplePerson simplepers0_ where simplepers0_.name=?
Hibernate: select simplepers0_.id as id0_, simplepers0_.name as name0_ from SimplePerson simplepers0_ where simplepers0_.name=?
Hibernate: select simplepers0_.id as id0_, simplepers0_.name as name0_ from SimplePerson simplepers0_ where simplepers0_.name=?

我对二级缓存的理解有什么问题？为什么Hibernate运行查询4次？我是否会错过一些配置？

迈克尔,提前谢谢

Answer 1

javax.persistence.Query中没有setCacheable方法,因此您需要将缓存提示添加到命名查询(或调用setHint):

@NamedQueries({
@NamedQuery(
    name="SimplePerson.findByName", 
    query="select p from SimplePerson p where p.name = :name", 
    hints = { @QueryHint(name = "org.hibernate.cacheable", value = "true") })
})

也就是说,使用查询缓存已经跳过了鲨鱼,如果你甚至要考虑它,下面的文章是必读的.现在有更好的方法,如Spring Caching抽象.