Spring-data 无法更新 id 为 0 的对象

Question

我有以下实体类：

@Entity
public class Item {
    @Id
    private long id;
    private String name;
    //getters & setters
}

一个标准的回购：

public interface Repo extends CrudRepository<Item, Long> {}

一个简单的restController：

@RestController
public class Controller {
    @Autowired
    private Repo repo;

    @GetMapping("1")
    public Iterable<Item> getItems1() {
        Item item = new Item();
        item.setId(1);
        item.setName("name1");
        repo.save(item);

        item = new Item();
        item.setId(1);
        item.setName("name11");
        repo.save(item);

        return repo.findAll();
    }

    @GetMapping("0")
    public Iterable<Item> getItems0() {
        Item item = new Item();
        item.setId(0);
        item.setName("name0");
        repo.save(item);

        item = new Item();
        item.setId(0);
        item.setName("name00");
        repo.save(item);

        return repo.findAll();
    }
}

依赖项：spring-boot-starter-web、spring-boot-starter-data-jpa 和 com.h2database:h2。

测试：

curl -si http://localhost:8080/1
HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked

[{"id":1,"name":"name11"}]

curl -si http://localhost:8080/0
HTTP/1.1 500
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
Connection: close

{"timestamp":"2019-05-09T16:45:01.734+0000","status":500,"error":"Internal Server Error","message":"A different object with the same identifier value was already associated with the session : [test.Item#0]; nested exception is javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [test.Item#0]","path":"/0"}

为什么使用 id 1（或任何其他 id）存储可以正常工作并正确更新实体，而使用 id 0 存储总是在第二次存储时失败？

我用谷歌搜索了这个异常并理解它可能与休眠有关，认为它是一个未初始化的 id？但是无法理解它是如何进入这个异常的确切逻辑。

堆栈跟踪：

javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [test.Item#0]
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:118) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:157) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:164) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:790) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:768) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202]
at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:350) ~[spring-orm-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at com.sun.proxy.$Proxy74.persist(Unknown Source) ~[na:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202]
at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:305) ~[spring-orm-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at com.sun.proxy.$Proxy74.persist(Unknown Source) ~[na:na]
at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:490) ~[spring-data-jpa-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202]
at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:377) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:200) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:641) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:605) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:590) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:59) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:294) ~[spring-tx-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98) ~[spring-tx-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139) ~[spring-tx-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:135) ~[spring-data-jpa-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:61) ~[spring-data-commons-2.0.10.RELEASE.jar:2.0.10.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at com.sun.proxy.$Proxy76.save(Unknown Source) ~[na:na]
at test.Controller.getItems0(Controller.java:37) ~[classes/:na] <-- when saving (0, "item00")

Answer 1

看SimpleJpaRepository.save的实现

@Transactional
public <S extends T> S save(S entity) {

    if (entityInformation.isNew(entity)) {
        em.persist(entity);
        return entity;
    } else {
        return em.merge(entity);
    }
}

比检查AbstractEntityInformation.isNew。它得出的结论是，只有当实体为空（或数字类型为 0）时，实体才是新的。

您有两种选择来处理这种情况：

• 使用entityManager.persist 或entityManager.merge 代替spring 数据存储库
• 派生自org.springframework.data.domain.Persistable并实现isNew()