Hibernate缓存和延迟加载的关联

Question

我得到了一个典型的订单和物品的实体关联。为了使只读订单成为可能，项目设置为默认FetchType.LAZY。2级和查询缓存已启用。要读取具有关联项目的订单，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中，引发了LazyInitializationException异常，因为未初始化项目（未从缓存还原）。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;
  ...
}

道：

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：

<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代替JPA缓存。我还尝试了JPA实体图而不是JOIN FETCH。始终相同：在第二次调用订单查询时未初始化/还原项目。

Answer 1

我认为@Cacheable不是Hibernate缓存，而是Spring缓存。@Cache注解用于Hibernate缓存。除此之外，当我遇到这些问题时，为了使 JOIN FETCH 结果也可用于缓存，我必须将 Hibernate.initialize(...) 添加到 Dao 方法以避免 LazyInitializationException。