Hibernate Projections / Lazy Loading for non required 1 to 1 Mappings

Question

I have the following 2 classes (trimmed down for this post)

public class ApplicationVO implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = -3314933694797958587L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    private Integer id;


    @OneToOne(fetch = FetchType.LAZY, mappedBy = "application")
    @Cascade({ CascadeType.ALL })
    @JsonIgnore
    private ApplicationHomeScreenVO applicationHomeScreen;

...
...
... 
}


public class ApplicationHomeScreenVO implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = -9158898930601867545L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    @JsonProperty("id")
    private Integer id;

    @OneToOne(fetch = FetchType.LAZY)
    @Cascade({ CascadeType.SAVE_UPDATE })
    @JoinColumn(name="application_id")
    @JsonProperty("application")
    protected ApplicationVO application;    

    ...
    ...
    ...
}

I am trying to load an applicationById wuthout loading the applicationHomeScreen Unfortunately the lazy loading doesnt seem to be working. I have looked at other posts and they recommend setting the option=false flag on the @OneToOne annotation but unfortunately, applicationHomeScreen can be optional

I am now trying to use projections but that is not working either for me either

When I call the following method

 public ApplicationVO findApplicationById(Integer applicationId) {

        Criteria criteria = currentSession().createCriteria(ApplicationVO.class);
        criteria.add(Restrictions.eq("id", applicationId));

        criteria.setProjection(Projections.projectionList()
                .add(Projections.property("applicationHomeScreen"), "applicationHomeScreen"))
              .setResultTransformer(Transformers.aliasToBean(ApplicationVO.class));

        ApplicationVO applicationVO = (ApplicationVO) criteria.uniqueResult();

        return applicationVO;
    }

I get the stack trace

java.lang.ArrayIndexOutOfBoundsException: 0
    at org.hibernate.loader.criteria.CriteriaLoader.getResultRow(CriteriaLoader.java:168)
    at org.hibernate.loader.criteria.CriteriaLoader.getResultColumnOrRow(CriteriaLoader.java:148)
    at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:754)
    at org.hibernate.loader.Loader.processResultSet(Loader.java:953)
    at org.hibernate.loader.Loader.doQuery(Loader.java:921)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:355)
    at org.hibernate.loader.Loader.doList(Loader.java:2554)
    at org.hibernate.loader.Loader.doList(Loader.java:2540)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2370)
    at org.hibernate.loader.Loader.list(Loader.java:2365)
    at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:126)
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1682)
    at org.hibernate.internal.CriteriaImpl.list(CriteriaImpl.java:380)
    at org.hibernate.internal.CriteriaImpl.uniqueResult(CriteriaImpl.java:402)
    at com.dao.database.impl.ApplicationDAOImpl.findApplicationById(ApplicationDAOImpl.java:349)

Can anyone recommend an approach I can use to either a) get lazy loading working properly for one to one mappings where the association is not required b) get projections working so I dont need to load any child associations if they are not needed

Thank you Damien

Answer 1

The only option is to follow these steps:

1. Add @LazyToOne to the one-to-one association:

   @OneToOne(fetch = FetchType.LAZY, mappedBy = "application")
   @Cascade({ CascadeType.ALL })
   @JsonIgnore
   @LazyToOne(value = LazyToOneOption.NO_PROXY)
   private ApplicationHomeScreenVO applicationHomeScreen;
   

2. Configure bytecode enhancement

Answer 2

Optional @OneToOne relationships cannot be lazy because the non-owning side of the relationship does not now whether the child exists(optional) - Hibernate doesn't know whether to put a proxy object or null. There are several workarounds for this. This link has detailed explanation on some workarounds