Question

我的Parent实体有一个Child实体和Element s的集合：

@Entity
public class Parent {
    @Id
    private String id;

    @OneToOne(cascade = CascadeType.ALL)
    private Child child;

    @ManyToMany(cascade = CascadeType.ALL)
    private List<Element> elements;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public Child getChild() {
        return child;
    }

    public void setChild(Child child) {
        this.child = child;
    }

    public List<Element> getElements() {
        return elements;
    }

    public void setElements(List<Element> elements) {
        this.elements = elements;
    }

}

Child实体也有Element个集合，但它仅限于包含Parent Element集合中的元素。（但不一定都是全部）。

@Entity
public class Child {
    @Id
    private String id;

    @ManyToMany
    private List<Element> elements;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public List<Element> getElements() {
        return elements;
    }

    public void setElements(List<Element> elements) {
        this.elements = elements;
    }
}

以下是Element实体：

@Entity
public class Element {

    public Element() {}

    public Element(String id) {
        this.id = id;
    }

    @Id
    private String id;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @Override
    public boolean equals(Object other) {
        if (!(other instanceof Element)) {
            return false;
        }
        return id.equals(((Element) other).getId());
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(id);
    }
}

我想将Parent的实例传递给save()方法，以便自动创建顶级Element集合（这就是我向第一个添加级联选项的原因）。 Parent Child实例也应该保存，但不应该创建它的元素，而应该创建对顶级集合中已存在的元素的引用（所以Child）中没有级联。

但是，以下代码会产生异常（Spring JPARepository内部调用EntityManager.merge()）

    Parent parent = new Parent();
    parent.setId("someId");

    Element element1 = new Element("id1");
    Element element2 = new Element("id2");
    Element element3 = new Element("id3");

    Element element1Copy = new Element("id1");
    Element element3Copy = new Element("id3");

    List<Element> originalElements = new ArrayList<Element>();
    originalElements.add(element1);
    originalElements.add(element2);
    originalElements.add(element3);
    parent.setElements(originalElements);

    Child child = new Child();
    child.setId("childId");
    parent.setChild(child);
    List<Element> elementsCopies = new ArrayList<Element>();
    elementsCopies.add(element1Copy);
    elementsCopies.add(element3Copy);
    child.setElements(elementsCopies);


    Parent saved = parentRepository.save(parent);

堆栈追踪：

Caused by: org.springframework.orm.jpa.JpaObjectRetrievalFailureException: Unable to find org.daniel.model.Element with id id1; nested exception is javax.persistence.EntityNotFoundException: Unable to find org.daniel.model.Element with id id1
    at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:389) ~[spring-orm-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:246) ~[spring-orm-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:491) ~[spring-orm-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:59) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:213) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:147) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133) ~[spring-data-jpa-1.10.5.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at com.sun.proxy.$Proxy73.save(Unknown Source) ~[na:na]
    at org.daniel.Monitor.createAndSave(Monitor.java:47) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_40]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_40]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_40]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_40]
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(InitDestroyAnnotationBeanPostProcessor.java:366) ~[spring-beans-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeInitMethods(InitDestroyAnnotationBeanPostProcessor.java:311) ~[spring-beans-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:134) ~[spring-beans-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    ... 23 common frames omitted
Caused by: javax.persistence.EntityNotFoundException: Unable to find org.daniel.model.Element with id id1
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$JpaEntityNotFoundDelegate.handleEntityNotFound(EntityManagerFactoryBuilderImpl.java:144) ~[hibernate-entitymanager-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:278) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.doOnLoad(DefaultLoadEventListener.java:121) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:89) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1129) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.internalLoad(SessionImpl.java:1022) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:639) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.EntityType.resolve(EntityType.java:431) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.EntityType.replace(EntityType.java:330) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.CollectionType.replaceElements(CollectionType.java:518) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.CollectionType.replace(CollectionType.java:663) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.AbstractType.replace(AbstractType.java:147) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.type.TypeHelper.replaceAssociations(TypeHelper.java:261) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.copyValues(DefaultMergeEventListener.java:427) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:240) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:301) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:170) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:850) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:832) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.engine.spi.CascadingActions$6.cascade(CascadingActions.java:260) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:398) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:162) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:111) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeBeforeSave(AbstractSaveEventListener.java:425) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:232) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:301) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:170) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:69) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:840) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:822) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:827) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:1161) ~[hibernate-entitymanager-5.0.11.Final.jar:5.0.11.Final]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_40]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_40]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_40]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_40]
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:298) ~[spring-orm-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at com.sun.proxy.$Proxy71.merge(Unknown Source) ~[na:na]
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:509) ~[spring-data-jpa-1.10.5.RELEASE.jar:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_40]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_40]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_40]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_40]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:503) ~[spring-data-commons-1.12.5.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:488) ~[spring-data-commons-1.12.5.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:460) ~[spring-data-commons-1.12.5.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61) ~[spring-data-commons-1.12.5.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136) ~[spring-tx-4.3.4.RELEASE.jar:4.3.4.RELEASE]
    ... 38 common frames omitted

我理解它的方式是Hibernate首先处理子进程（在顶级元素集合之前）并且它找不到应该与Child实例关联的Element实例，因为它们是在持久化顶级元素时创建的采集。

Hibernate / JPA如何解决这个问题？我是否可以指示它以我想要的方式保持我的结构，而不会回到手动逐场保存？

Answer 1

您当前的问题源于您设置了实体的ID，而实体的ID没有版本属性。因此，Spring认为这是一个已经存在的实体，并尝试将其与当前的EntityManager合并。但实际上它是一个新的实例。

因此，为了解决此问题，您可以执行以下操作之一：

为您的实体添加属性，并使用@Version
让JPA生成您的ID

我推荐第一种方法，因为版本属性也有其他原因。

但是你的问题不会在那里停止：你正在创建具有相同类型和id的多个实体，一旦解决了其他问题，这将导致异常。

而是使用相同的实例，如下所示：

    Parent parent = new Parent();
    parent.setId("someId");

    Element element1 = new Element("id1");
    Element element2 = new Element("id2");
    Element element3 = new Element("id3");

    List<Element> originalElements = new ArrayList<Element>();
    originalElements.add(element1);
    originalElements.add(element2);
    originalElements.add(element3);
    parent.setElements(originalElements);

    Child child = new Child();
    child.setId("childId");
    parent.setChild(child);
    List<Element> elementsCopies = new ArrayList<Element>();
    elementsCopies.add(element1);
    elementsCopies.add(element3);
    child.setElements(elementsCopies);


    Parent saved = parentRepository.save(parent);

对您的假设做出更多评论

我想将Parent的实例传递给save（）方法，以便自动创建顶级Element集合（这就是为什么我将cascade选项添加到第一个）。

你必须创建这个集合，JPA不会为你做这件事（但这似乎只是一个措辞问题，因为你在你的代码中做得很好）
< / LI>
级联选项几乎与为实体创建的记录无关，但仅限于。使用CascadeType.ALL引用的实体将在手头的实体保存时保存。没有级联，你必须自己保存。如果你不这样做，JPA将对一个不存在的实体进行例外处理

也应保存父亲的子实例，但不应创建它的元素，而应创建对顶级集合中已存在的元素的引用（因此在子级中不存在级联）。

再次，cascade与仅由谁负责创建数据库记录无关。
如果你想在JPA中的东西引用相同的第三件事，只需使用第三件事的相同实例。 JPA会解决这个问题。

我理解它的方式是Hibernate首先处理子进程（在顶级元素集合之前）并且它找不到应该与Child实例关联的Element实例，因为它们是在持久化顶级元素时创建的集合。

如上所述，这根本不是问题。一旦你给JPA提供了你想要保存的实例图，它就会找出正确的顺序（几乎在所有情况下）。

如何在同一个Spring Data JPA保存请求中级联创建和存储引用？

1 个答案: