java – Hibernate缓存和延迟加载的关联

我有一个典型的订单和物品实体关联.为了能够只读订单,设置的项是默认的FetchType.LAZY.启用了第二级和查询缓存.要阅读包含相关项目的订单,我正在使用JPQL查询.查询和实体由EHCache缓存.但是在访问项目时的第二次调用时,抛出了LazyInitializationException,因为项目未初始化(未从缓存中恢复).为什么?实施此要求的最佳方法是什么?

订购:

@Entity
@Cacheable
@NamedQueries({
  @NamedQuery(name = Order.NQ_FIND_BY_ID_FETCH_ITEMS, query = "SELECT DISTINCT o FROM Order o JOIN FETCH o.items WHERE o.id = :id")
})
@Table(...)
public class Order extends ... {
  ...
  @OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
  // @Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
  private Set<Item> items = new HashSet<Item>();
  ...
}

项目:

@Entity
@Cacheable
@Table(...)
public class Item extends ... {
  @ManyToOne
  @JoinColumn(name = "order_id", nullable = false)
  private Order order;
  ...
}

DAO:

public class OrderDaoJpaImpl extends ... {

  @Override
  public Catalog findByIdFetchItems(Long id) {
    TypedQuery<Order> query = entityManager.createNamedQuery(Order.NQ_FIND_BY_ID_FETCH_ITEMS, Order.class);
    query.setParameter("id", id);
    // query.setHint(QueryHints.HINT_CACHEABLE, Boolean.TRUE);
    Order order = JPAUtil.singleResultOrNull(query);
    return order;
}

服务:

@Service("orderService")
@Transactional(propagation = Propagation.SUPPORTS, readOnly = true)
public class OrderServiceImpl implements OrderService {

  @Override
  public Order getOrderWithItems(Long orderId) {
    return orderDao.findByIdFetchItems(orderId);
  }
}

persistence.xml中:

<persistence ...>
  <persistence-unit name="shop-persistence" transaction-type="RESOURCE_LOCAL">
    <jar-file>shop-persistence.jar</jar-file>
    <!-- Enable JPA 2 second level cache -->
    <shared-cache-mode>ALL</shared-cache-mode>
    <properties>
      ...
      <property name="hibernate.cache.use_second_level_cache" value="true" />
      <property name="hibernate.cache.use_query_cache" value="true" />
      <property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory"/>
    </properties>
  </persistence-unit>
</persistence>

Spring Framework 4.3.7.RELEASE和Hibernate 5.2.9.Final.

如您所见,我尝试使用Hibernate实体注释和缓存提示而不是JPA缓存.我也尝试过JPA实体图而不是JOIN FETCH.始终相同:在订单查询的第二次调用中未初始化/恢复项目.

最佳答案 由于
HHH-12430问题,抛出了LazyInitializationException.

但是,您的代码也存在一些问题,并且在Hibernate HHH-12430问题得到修复之前,您可以使用一种解决方法.

当您使用Hibernate时,使用@Cacheable注释您的实体是不够的.

this article中所述,您还需要提供缓存并发策略:

@Entity
@org.hibernate.annotations.Cache(usage = 
    CacheConcurrencyStrategy.READ_WRITE)

查询缓存only stores entity identifiers,由于您只选择订单,因此项目关联也不会被缓存.

你可以做的是将你的查询更改为:

@NamedQuery(name = Order.NQ_FIND_BY_ID_FETCH_ITEMS, query = "SELECT DISTINCT o FROM Order o WHERE o.id = :id")

然后,激活缓存以进行收集:

@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
private Set<Item> items = new HashSet<Item>();

订单和物品都应该使用:

@Entity
@org.hibernate.annotations.Cache(usage = 
    CacheConcurrencyStrategy.READ_WRITE)

因为它们需要可缓存.

并确保在返回结果集之前初始化items集合:

Order order = JPAUtil.singleResultOrNull(query);
if(order != null) {
    order.getItems().size();
}
return order;

这样,将始终初始化项目,并从缓存中提取集合,而不是从数据库中提取集合.

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