避免通过Hibernate Criteria或HQL查询进行辅助选择或联接

避免通过Hibernate Criteria或HQL查询进行辅助选择或联接

如前所述

我想要一个 可以控制 执行查询时 延迟加载的内容 的解决方案

如果您有这样的映射

@Entitypublic class GiftCard implements Serializable {    private User buyer;    @ManyToOne    @JoinColumn(name="buyerUserId")    public User getBuyer() {        return this.buyer;    }}

默认情况下，任何
ToOne关系（例如@OneToOne和@ManyToOne）都是FetchType.EAGER，这意味着将始终对其进行提取。但是，这可能不是您想要的。当
我可以控制延迟加载的内容时， 您所说的 内容 可以翻译为“

获取策略”*
。Action
Book中的POJO支持这种模式（Notice方法签名）

public class GiftCardRepositoryImpl implements GiftCardRepository {     public List<GiftCard> findGiftCardWithBuyer() {         return sessionFactory.getCurrentSession().createQuery("from GiftCard c inner join fetch c.buyer where c.recipientNotificationRequested = 1").list();     }}

因此，根据您的用例，您可以创建自己的 find … With … And … 方法。它会照顾 您想要的东西

但这有一个问题：它不支持通用方法签名。对于每个@Entity存储库，您必须定义自定义 find … With … And
方法。因此，我向您展示了如何定义通用存储库

public interface Repository<INSTANCE_CLASS, UPDATABLE_INSTANCE_CLASS, PRIMARY_KEY_CLASS> {    void add(INSTANCE_CLASS instance);    void remove(PRIMARY_KEY_CLASS id);    void update(PRIMARY_KEY_CLASS id, UPDATABLE_INSTANCE_CLASS updatableInstance);    INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id);    INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id, FetchingStrategy fetchingStrategy);    List<INSTANCE_CLASS> findAll();    List<INSTANCE_CLASS> findAll(FetchingStrategy fetchingStrategy);    List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize);    List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize, FetchingStrategy fetchingStrategy);    List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria);    List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria, FetchingStrategy fetchingStrategy);    List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria);    List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, FetchingStrategy fetchingStrategy);}

但是， 有时
，您不希望通用存储库接口定义所有方法。解决方案：创建一个AbstractRepository类，它将实现一个虚拟存储库。例如，Spring
framework 大量使用这种模式 接口>> AbstractInterface

public abstract class AbstractRepository<INSTANCE_CLASS, UPDATABLE_INSTANCE_CLASS, PRIMARY_KEY_CLASS> implements Repository<INSTANCE_CLASS, UPDATABLE_INSTANCE_CLASS, PRIMARY_KEY_CLASS> {    public void add(INSTANCE_CLASS instance) {        throw new UnsupportedOperationException("Not supported yet.");    }    public void remove(PRIMARY_KEY_CLASS id) {        throw new UnsupportedOperationException("Not supported yet.");    }    public void update(PRIMARY_KEY_CLASS id, UPDATABLE_INSTANCE_CLASS updatableInstance) {        throw new UnsupportedOperationException("Not supported yet.");    }    public INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id) {        throw new UnsupportedOperationException("Not supported yet.");    }    public INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id, FetchingStrategy fetchingStrategy) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAll() {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAll(FetchingStrategy fetchingStrategy) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize, FetchingStrategy fetchingStrategy) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria, FetchingStrategy fetchingStrategy) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria) {        throw new UnsupportedOperationException("Not supported yet.");    }    public List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, FetchingStrategy fetchingStrategy) {        throw new UnsupportedOperationException("Not supported yet.");    }}

因此，您的GiftCardRepository可以重写为（请参见扩展而不是工具），并且 可以覆盖您真正想要的内容

public class GiftCardRepository extends AbstractRepository<GiftCard, GiftCard, String> {    public static final GIFT_CARDS_WITH_BUYER GIFT_CARDS_WITH_BUYER = new GIFT_CARDS_WITH_WITH_BUYER();    public static final GIFT_CARDS_WITHOUT_NO_RELATIonSHIP GIFT_CARDS_WITHOUT_NO_RELATIonSHIP = new GIFT_CARDS_WITHOUT_NO_RELATIonSHIP();    public List<GiftCard> findAll(FetchingStrategy fetchingStrategy) {        sessionFactory.getCurrentSession().getNamedQuery(fetchingStrategy.toString()).list();    }        private static class GIFT_CARDS_WITH_BUYER extends AbstractFetchingStrategy {}        private static class GIFT_CARDS_WITHOUT_NO_RELATIonSHIP extends AbstractFetchingStrategy {}}

现在，我们将命名查询外部化为多行且可读且可维护的xml文件

// app.hbl.xml<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <query name="GIFT_CARDS_WITH_BUYER">        <![CDATA[ from      GiftCard c left join fetch      c.buyer where     c.recipientNotificationRequested = 1        ]]>    </query>    <query name="GIFT_CARDS_WITHOUT_NO_RELATIONSHIP">        <![CDATA[ from      GiftCard        ]]>    </query></hibernate-mapping>

因此，如果您想与买家一起找回GiftCard，只需致电

Repository<GiftCard, GiftCard, String> giftCardRepository;List<GiftCard> giftCardList = giftCardRepository.findAll(GiftCardRepository.GIFT_CARDS_WITH_WITH_BUYER);

并要获取没有任何关系的GiftCard，只需致电

List<GiftCard> giftCardList = giftCardRepository.findAll(GiftCardRepository.GIFT_CARDS_WITHOUT_NO_RELATIONSHIP);

或使用import static

import static packageTo.GiftCardRepository.*;

和

List<GiftCard> giftCardList = giftCardRepository.findAll(GIFT_CARDS_WITHOUT_NO_RELATIONSHIP);

希望对您有用！