避免使用Hibernate Criteria或HQL查询进行二次选择或连接

Question

我在优化Hibernate查询时遇到问题,以避免执行连接或二次选择.

执行Hibernate查询(条件或hql)时,如下所示:

return getSession().createQuery(("from GiftCard as card where card.recipientNotificationRequested=1").list();

...和where子句检查不需要与其他表连接的属性...但是Hibernate仍然与其他表执行完全连接(或者根据我设置fetchMode的方式进行二次选择).

有问题的对象(GiftCard)有一些ManyToOne关联,在这种情况下我宁愿懒洋洋地加载(但不一定是所有情况).我想要一个解决方案,我可以控制在执行查询时延迟加载的内容.

这就是GiftCard实体的样子:

@Entity
@Table(name = "giftCards")
public class GiftCard implements Serializable
{
 private static final long serialVersionUID = 1L;

 private String id_;
 private User buyer_;
 private boolean isRecipientNotificationRequested_;


 @Id
 public String getId()
 {
  return this.id_;
 }

 public void setId(String id)
 {
  this.id_ = id;
 }

 @ManyToOne
 @JoinColumn(name = "buyerUserId")
 @NotFound(action = NotFoundAction.IGNORE)
 public User getBuyer()
 {
  return this.buyer_;
 }
 public void setBuyer(User buyer)
 {
  this.buyer_ = buyer;
 }

 @Column(name="isRecipientNotificationRequested", nullable=false, columnDefinition="tinyint")
 public boolean isRecipientNotificationRequested()
 {
  return this.isRecipientNotificationRequested_;
 }

 public void setRecipientNotificationRequested(boolean isRecipientNotificationRequested)
 {
  this.isRecipientNotificationRequested_ = isRecipientNotificationRequested;
 }
}

Answer 1

正如所说

我想要一个解决方案，可以控制执行查询时延迟加载的内容

如果您有这样的映射

@Entity
public 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，这意味着它将始终被获取。但是，这不可能是你想要的。你所说的我可以控制延迟加载的内容可以翻译为获取策略。《POJO in Action》一书支持这样的模式（注意方法签名）

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。它会负责获取你想要的东西

但它有一个问题：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，我将向您展示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 框架大量使用这种模式Interface >> 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（请参阅扩展而不是实现），并且只需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();
    }


    /**
      * FetchingStrategy is just a marker interface
      * public interface FetchingStrategy {}
      *
      * And AbstractFetchingStrategy allows you to retrieve the name of the Fetching Strategy you want, by overriding toString method
      * public class AbstractFetchingStrategy implements FetchingStrategy {
      *
      *     @Override
      *     public String toString() {
      *         return getClass().getSimpleName();
      *     } 
      *
      * }
      * 
      * Because there is no need to create an instance outside our repository, we mark it as private
      * Notive each FetchingStrategy must match a named query
      */
    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到一个多行且可读且可维护的 xml 文件中

// 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，如果您想向买家取回礼品卡，只需致电

Repository<GiftCard, GiftCard, String> giftCardRepository;

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

要在没有任何关系的情况下取回我们的礼品卡，只需致电

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

或使用导入静态

import static packageTo.GiftCardRepository.*;

和

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

我希望它对你有用！