將JoinColumn中的空字符串視為null

Question

我目前正在使用以下方案進行項目：

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

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

這里最重要的部分是從Profile到Function的外鍵（ CODE_FUNCTION => CODE ）。

但是，並非每個配置文件都具有功能，因此在某些情況下，CODE_FUNCTION只是空白行（ " " ）。

我通過使用以下方式映射了該函數（在Profile ）：

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

在Function表中，使用以下方式映射代碼：

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

當配置文件具有功能時，這可以正常工作，但是，當沒有輸入功能代碼時，出現以下錯誤：

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

這里的問題（我假設）是，因為我們使用的是空字符串（而不是NULL`），所以映射失敗，因為它正在嘗試查找具有該ID的函數。

有沒有一種方法可以在不調整所有表記錄並將這些空字符串替換為NULL情況下防止這種情況發生？ 例如，我知道我可以使用實體偵聽器來處理某些字段，但是可以對使用@JoinColumn注釋的字段執行相同的@JoinColumn嗎？

Answer 1

添加@NotFound批注

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

Answer 2

如果僅使用@NotFound（action = NotFoundAction.IGNORE），則強制Hibernate對每個缺少的FK發出附加的SELECT請求。 實際上，我找到了一個更好的解決方案：使用@JoinFormula。

所以代替：

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

采用：

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

這樣，Hibernate會將空關系識別為實際的NULLS。