概述：
我正在构建一个spring-boot应用程序，它部分地从外部REST服务中检索一些实体，并将它与数据库中本地保存的实体的先前版本进行比较。
我正在使用EntityManager注入@PersistenceContext，并使用它来处理数据库，因为有许多实体类型，并且该类型最初是模块未知的。我可以从工厂获得一个JpaRepository，但不同实体类型的数量可能会增长，如果可能的话，我宁愿不依赖它。
问题：
当模块检索它在数据库中没有保存的实体时，它会执行一些业务逻辑，然后尝试保留新实体。
Person类是有问题的实体之一，它包含三个类型为Site的字段，它们通常包含相同的对象。
当我尝试在Person的多个字段中保持一个新的Site具有相同的CascadeType.PERSIST对象时，我得到一个EntityExistsException（参见stacktrace（1））。
当我从Site字段中删除CascadeType.PERSIST，并尝试在多个字段中保留一个具有相同Person对象的新Site时，我得到一个TransientPropertyValueException（请参阅stacktrace（2））。
我想我理解两种异常发生的原因：
@Transactional注释试图在没有持久化站点实例的情况下刷新事务。我已经尝试删除@Transactional注释并开始并自己提交EntityTransaction，但我得到了一个IllegalStateException（参见stacktrace（3）），尽管我认为这是预期的，因为spring应该处理事务本身。
我看过类似问题的答案（例如this，this），但都提出了改变CascadeType的一些变化。
在另一个问题中，有人建议确保通过equals()方法正确评估有问题的实体，因此我检查了调试器，并且((Person)newEntity).currentSite.equals(((Person)newEntity).homeSite)评估为true。
如何在多个字段中使用相同对象持续持久/合并实体？
编辑：我也尝试过使用fetch = FetchType.EAGER的级联类型的各种组合，但是它们各自的异常没有变化。
编辑2：我尝试使用JpaRepository而不是使用EntityManager，并根据我正在使用的级联类型获得有效的同一组异常。
如果我使用PERSIST，但没有使用MERGE，我会得到一个EntityNotFoundException（参见stacktrace（4）），如果我同时使用PERSIST和MERGE，我会得到一个InvalidDataAccessApiUsageException`（参见stacktrace（5））。
人：
@EqualsAndHashCode(callSuper = true)
@javax.persistence.Entity
@XmlDiscriminatorValue("person")
@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({Subscriber.class})
public class Person extends MobileResource implements Serializable {
private static final Logger LOG = LogManager.getLogger(Person.class);
private String firstName;
private String surname;
public Person() {
super();
}
public Person(Long id) {
super(id);
}
public Person(Person that) {
super(that);
this.firstName = that.firstName;
this.surname = that.surname;
}
// getters && setters
}
MobileResource：
@EqualsAndHashCode(callSuper = true)
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@XmlRootElement(name = "resource")
@XmlDiscriminatorNode("@type")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({Vehicle.class, Person.class})
public abstract class MobileResource extends Resource implements Serializable {
private static final Logger LOG = LogManager.getLogger(MobileResource.class);
@ManyToOne(cascade = CascadeType.ALL)
private MobileResourceStatus status;
private Long incidentId;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.DETACH})
private Site homeSite;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.DETACH})
private Site currentSite;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.DETACH})
private Site relocationSite;
public MobileResource() {
super();
}
public MobileResource(Long id) {
super(id);
}
public MobileResource(MobileResource that) {
super(that);
this.status = that.status;
this.incidentId = that.incidentId;
this.homeSite = that.homeSite;
this.currentSite = that.currentSite;
this.relocationSite = that.relocationSite;
}
// getters && setters
}
现场：
@EqualsAndHashCode(callSuper = true)
@javax.persistence.Entity
public class Site extends Resource implements Serializable {
private static final Logger LOG = LogManager.getLogger(Site.class);
private String location;
public Site() {
super();
}
public Site(Long id) {
super(id);
}
public Site(Site that) {
super(that);
this.location = that.location;
}
}
资源：
@EqualsAndHashCode
@MappedSuperclass
@XmlRootElement
@XmlSeeAlso({MobileResource.class})
public abstract class Resource implements Entity, Serializable {
private static final Logger LOG = LogManager.getLogger(Resource.class);
@Id
private Long id;
private String callSign;
@XmlPath(".")
private LatLon latLon;
private Long brigadeId;
private Long batchId;
@ManyToMany(cascade = CascadeType.ALL)
private List<Attribute> attributes;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.DETACH})
private ResourceType type;
public Resource() {
}
public Resource(Long id) {
this.id = id;
}
public Resource(Resource that) {
this.id = that.id;
this.callSign = that.callSign;
this.latLon = that.latLon;
this.attributes = that.attributes;
this.batchId = that.batchId;
this.brigadeId = that.brigadeId;
this.type = that.type;
}
// getters && setters
}
DefaultEntityMessageHandler：
@Component
public class DefaultEntityMessageHandler implements EntityMessageHandler {
@PersistenceContext
private EntityManager entityManager;
@Override
@Transactional
public void handleEntityMessage(EntityMessageData data, Message message) {
// business logic
if (newEntity != null) {
if (oldEntity != null)
entityManager.merge(newEntity);
else
entityManager.persist(newEntity);
}
}
}
Stacktrace（1）：
2018-06-06 12:05:15,975 ERROR ActiveMQMessageConsumer - ID:cpt-9225-1528283097161-1:1:1:1 Exception while processing message: ID:cpt-8919-1528281875592-1:1:1:1:4
javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [my.class.path.entity.resource.site.Site#738]
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:118)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:157)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:164)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:813)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:773)
at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80)
at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:467)
at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:392)
at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193)
at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:126)
at org.hibernate.event.internal.AbstractSaveEventListener.cascadeBeforeSave(AbstractSaveEventListener.java:414)
at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:252)
at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:182)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67)
at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132)
...
更改MobileResource中的级联类型：
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.REMOVE, CascadeType.DETACH})
private Site homeSite;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.REMOVE, CascadeType.DETACH})
private Site currentSite;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.REMOVE, CascadeType.DETACH})
Stacktrace（2）：
2018-06-06 12:19:24,084 ERROR ExceptionMapperStandardImpl - HHH000346: Error during managed flush [org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : my.class.path.entity.resource.mobile_resource.person.Person.currentSite -> my.class.path.entity.resource.site.Site]
2018-06-06 12:19:24,093 ERROR ActiveMQMessageConsumer - ID:cpt-9436-1528283955454-1:1:1:1 Exception while processing message: ID:cpt-8919-1528281875592-1:1:1:1:8
org.springframework.dao.InvalidDataAccessApiUsageException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : my.class.path.entity.resource.mobile_resource.person.Person.currentSite -> my.class.path.entity.resource.site.Site; nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : my.class.path.entity.resource.mobile_resource.person.Person.currentSite -> my.class.path.entity.resource.site.Site
at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:365)
at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:227)
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:540)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:746)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:714)
...
Stacktrace（3）：
2018-06-06 13:29:35,594 ERROR ActiveMQMessageConsumer - ID:cpt-9864-1528288166188-1:1:1:1 Exception while processing message: ID:cpt-8919-1528281875592-1:1:1:1:9
java.lang.IllegalStateException: Not allowed to create transaction on shared EntityManager - use Spring transactions or EJB CMT instead
at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:254)
at com.sun.proxy.$Proxy114.getTransaction(Unknown Source)
at my.class.path.entity_controller.DefaultEntityMessageHandler.handleEntityMessage(DefaultEntityMessageHandler.java:60)
at my.class.path.entity_listener.listeners.IdExtractorMessageListener.onMessage(IdExtractorMessageListener.java:41)
...
Stacktrace（4）
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2018-06-06 15:26:36,143 ERROR SpringApplication - Application run failed
java.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:793)
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:774)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:335)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1246)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1234)
at my.class.path.OfficerSubscription.main(OfficerSubscription.java:44)
Caused by: org.springframework.orm.jpa.JpaObjectRetrievalFailureException: Unable to find my.class.path.entity.resource.site.Site with id 738; nested exception is javax.persistence.EntityNotFoundException: Unable to find my.class.path.entity.resource.site.Site with id 738
at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:373)
at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:227)
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:507)
at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:61)
at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:242)
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:153)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
...
Stacktrace（5）
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2018-06-06 15:31:54,840 ERROR SpringApplication - Application run failed
java.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:793)
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:774)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:335)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1246)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1234)
at my.class.path.OfficerSubscription.main(OfficerSubscription.java:44)
Caused by: org.springframework.dao.InvalidDataAccessApiUsageException: Multiple representations of the same entity [my.class.path.entity.resource.site.Site#738] are being merged. Detached: [FJE84 - Uckfield]; Detached: [FJE84 - Uckfield]; nested exception is java.lang.IllegalStateException: Multiple representations of the same entity [my.class.path.entity.resource.site.Site#738] are being merged. Detached: [FJE84 - Uckfield]; Detached: [FJE84 - Uckfield]
at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:365)
at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:227)
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:507)
at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:61)
at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:242)
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:153)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:135)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
at org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:61)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212)
at com.sun.proxy.$Proxy122.save(Unknown Source)
at my.class.path.OfficerSubscription.run(OfficerSubscription.java:81)
at my.class.path.OfficerSubscription$$FastClassBySpringCGLIB$$705870eb.invoke(<generated>)
...
经过几天的搜索，我终于在春季启动项目中解决了这个问题。
在application.yaml文件中添加以下块：
jpa:
properties:
hibernate:
enable_lazy_load_no_trans: true
event:
merge:
entity_copy_observer: allow