Treat empty string in JoinColumn as null

Question

I'm currently working on a project with the following scheme:

Profile
-------
CODE          |  CHAR(6)
CODE_FUNCTION |  CHAR(2)

Function
--------
CODE          |  CHAR(2)

The most important part here is the foreign key from Profile to Function (CODE_FUNCTION => CODE).

However, not each profile has a function, so in some cases the CODE_FUNCTION is just a blank row (" ").

I mapped the function (in Profile) by using:

@OneToOne
@JoinColumn(name = "CODE_FUNCTION", referencedColumnName = "CODE")
private Function function;

And in the Function table the code is mapped by using:

@Id
@Column(name = "CODE_FUNCTION")
private String code;

This is working properly when the profile has a function, however, the moment the function code is not entered, I'm getting the following error:

Caused by: javax.persistence.EntityNotFoundException: Unable to find org.example.entities.Function with id   
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$JpaEntityNotFoundDelegate.handleEntityNotFound(EntityManagerFactoryBuilderImpl.java:181)
    at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:218)
    at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:274)
    at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:150)
    at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1070)
    at org.hibernate.internal.SessionImpl.internalLoad(SessionImpl.java:989)
    at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:716)
    at org.hibernate.type.EntityType.resolve(EntityType.java:502)
    at org.hibernate.engine.internal.TwoPhaseLoad.doInitializeEntity(TwoPhaseLoad.java:170)
    at org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:144)
    at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1114)
    at org.hibernate.loader.Loader.processResultSet(Loader.java:972)
    at org.hibernate.loader.Loader.doQuery(Loader.java:920)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:354)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:324)
    at org.hibernate.loader.Loader.loadEntity(Loader.java:2148)
    at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:78)
    at org.hibernate.loader.entity.EntityLoader.loadByUniqueKey(EntityLoader.java:161)
    at org.hibernate.persister.entity.AbstractEntityPersister.loadByUniqueKey(AbstractEntityPersister.java:2385)
    at org.hibernate.type.EntityType.loadByUniqueKey(EntityType.java:767)
    at org.hibernate.type.EntityType.resolve(EntityType.java:505)
    at org.hibernate.engine.internal.TwoPhaseLoad.doInitializeEntity(TwoPhaseLoad.java:170)
    at org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:144)
    at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1114)
    at org.hibernate.loader.Loader.processResultSet(Loader.java:972)
    at org.hibernate.loader.Loader.doQuery(Loader.java:920)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:354)
    at org.hibernate.loader.Loader.doList(Loader.java:2553)
    at org.hibernate.loader.Loader.doList(Loader.java:2539)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2369)
    at org.hibernate.loader.Loader.list(Loader.java:2364)
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:496)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:387)
    at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:231)
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1264)
    at org.hibernate.internal.QueryImpl.list(QueryImpl.java:103)
    at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:573)
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:449)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.springframework.orm.jpa.SharedEntityManagerCreator$DeferredQueryInvocationHandler.invoke(SharedEntityManagerCreator.java:311)
    at com.sun.proxy.$Proxy77.getResultList(Unknown Source)
    at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:96)
    at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:61)
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:96)
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:86)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:337)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:96)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:260)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155)
    ... 92 more

The problem here (I assume) is that, because we're using an empty string (in stead of NULL`), the mapping is failing becasue it's trying to find the function with that ID.

Is there a way to prevent this from happening without adjusting all table records and replacing these empty strings by NULL? For example, I know I can use entity listeners to process certain fields, but can I do the same for fields annotated with @JoinColumn?

Answer 1

If you simply use @NotFound(action=NotFoundAction.IGNORE) you force Hibernate to make an additional SELECT request for every missing FK. Actually I found a better solution: use @JoinFormula.

So instead of:

@JoinColumn(name = "CODE_FUNCTION", referencedColumnName = "CODE")

use:

@JoinFormula(name = "NULLIF(CODE_FUNCTION, '')", referencedColumnName = "CODE")

That way empty relations are recognized as actuals NULLS by Hibernate.

Answer 2

add @NotFound annotation

@OneToOne
@JoinColumn(name = "CODE_FUNCTION", referencedColumnName = "CODE")
@NotFound(action=NotFoundAction.IGNORE)
private Function function;