Avoiding secondary selects or joins with Hibernate Criteria or HQL query

Question

I am having trouble optimizing Hibernate queries to avoid performing joins or secondary selects.

When a Hibernate query is performed (criteria or hql), such as the f

Answer 1

As said

I want a solution that I can control what is lazily loaded when I perform the query

If you have a mapping like this one

@Entity
public class GiftCard implements Serializable {

    private User buyer;

    @ManyToOne
    @JoinColumn(name="buyerUserId")
    public User getBuyer() {
        return this.buyer;
    }
}

Any *ToOne relationship, such as @OneToOne and @ManyToOne, is, by default, FetchType.EAGER which means it will be always fetched. But, it could not be what you want. What you say as I can control what is lazily loaded can be translated as Fetching Strategy. POJO in Action book supports a pattern like this one (Notice method signature)

public class GiftCardRepositoryImpl implements GiftCardRepository {

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

}

So based on your use case, you can create your own find...With...And... method. It will take care of fetching just what you want

But it has a problem: It does not support a generic method signature. For each @Entity repository, you have to define your custom find...With...And method. Because of that, i show you how i define a generic repository

public interface Repository {

    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 findAll();
    List findAll(FetchingStrategy fetchingStrategy);
    List findAll(int pageNumber, int pageSize);
    List findAll(int pageNumber, int pageSize, FetchingStrategy fetchingStrategy);
    List findAllByCriteria(Criteria criteria);
    List findAllByCriteria(Criteria criteria, FetchingStrategy fetchingStrategy);
    List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria);
    List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, FetchingStrategy fetchingStrategy);

}

But, sometimes, you do not want all of methods defined by generic Repository interface. Solution: create an AbstractRepository class which will implement a dummy repository. Spring Framework, for instance, heavily use this kind of pattern Interface >> AbstractInterface

public abstract class AbstractRepository implements Repository {

    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 findAll() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll(FetchingStrategy fetchingStrategy) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll(int pageNumber, int pageSize) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll(int pageNumber, int pageSize, FetchingStrategy fetchingStrategy) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(Criteria criteria) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(Criteria criteria, FetchingStrategy fetchingStrategy) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, FetchingStrategy fetchingStrategy) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

}

So your GiftCardRepository can be re-written as (See extends instead of implements) and just overrides what you really want

public class GiftCardRepository extends AbstractRepository {

    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 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 {}
}

Now we externalize our named query in a multiline - and readable and maintainable - xml file

// app.hbl.xml



    
        
    
    
        
    

So if you want to retrieve you GiftCard with Buyer, just call

Repository giftCardRepository;

List giftCardList = giftCardRepository.findAll(GiftCardRepository.GIFT_CARDS_WITH_WITH_BUYER);

And to retrieve our GiftCard without no relationship, just call

List giftCardList = giftCardRepository.findAll(GiftCardRepository.GIFT_CARDS_WITHOUT_NO_RELATIONSHIP);

or use import static

import static packageTo.GiftCardRepository.*;

And

List giftCardList = giftCardRepository.findAll(GIFT_CARDS_WITHOUT_NO_RELATIONSHIP);

I hope it can be useful to you!