Hibernate做了太多的查询

Question

我的申请中有一个性能问题。

我有三个实体，其关系如下：

one Order => many OrderLines => Many Cards

从数据库加载实体需要太多时间，orderLines加载的是急切加载，而Cards加载的是惰性加载。为了让应用流畅，懒惰加载是必要的。

我需要为一个案例配置即时加载，我需要帮助。

我正在使用jhsipster stack:spring boot和JPA

我试图编写Hql查询

@Query(value = "from Order as order "
        + "inner join order.orderLines as orderLines "
        + "inner join orderlines.cards gc "
        + "where order.id= :order")
Order findWithDependencies(@Param("order")Long order);

我有un错误：意外的令牌订单（第2行）

我尝试了原生查询

@Query(value = "select * "+ 
        "from order_table ot "+
        "left join order_line ol ON ot.id = ol.order_id "+
        "left join  giftcard gc ON gc.orderline_id = ol.id "+
        "where ot.id=:order", nativeQuery= true)
Order findWithDependenciesNative(@Param("order")Long order);

但当我这么做的时候

orderLine.getCard()

从代码中，Hibernate仍然执行查询以从数据库获取数据，这导致了我的性能问题。

必要的实体代码：

public class Order implements Serializable {
    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "order_id", nullable = false)
    @Size(min = 1)
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    @JsonProperty("detail")
    @Valid
    private List<OrderLine> orderLines = new ArrayList<>();
}
public class OrderLine extends AbstractAuditingEntity implements Serializable, Comparable {
    @OneToMany
    @JoinColumn(name = "orderline_id")
    @JsonIgnore
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    private Set<Giftcard> giftcards = new HashSet<>();
}

public class Giftcard extends AbstractAuditingEntity implements Serializable, Comparable {
    @ManyToOne(optional = true)
    @JoinColumn(name= "orderline_id")
    @JsonIgnore
    private OrderLine orderLine;
}

实际上是我的代码

{
    Order order = orderRepository.findWithDependenciesNative(linkFile.getOrder());
    //Some code
    List<OrderLine> orderLines = order.getOrderLines();
    orderLines.sort(Comparator.comparing(OrderLine::getId));
    for (OrderLine orderLine : orderLines) {
        Stream<Card> cards = orderLine.getCards().stream().sorted(Comparator.comparing(Card::getCardNumber));
        for (Card card : cards.collect(Collectors.toList())) {
        //Some code
        }
    }

问题是在第二个foreach中，对于每个卡，hibernate执行两个查询，而带有join的请求不会加载数据，比如eager配置。你有办法帮我吗？

非常感谢

Answer 1

使用“join fetch”避免延迟加载。“fetch”联接允许使用单个select来初始化值的关联或集合及其父对象。这在收集的情况下特别有用。它有效地覆盖了关联和集合的映射文件的外部联接和延迟声明。请参阅有关join fetch的更多信息：Hibernate中join和join fetch的区别

@Query("Select order from Order as order "
        + "inner join fetch order.orderLines as orderLines "
        + "inner join fetch orderlines.cards gc "
        + "where order.id= :order")
Order findWithDependencies(@Param("order")Long order);