java - 如何避免 javax.persistence.EntityExistsException : different object with the same identifier?

Question

我有一个小型学习项目，比如测验 API。当我尝试保存复杂对象(考试)时，hibernate 抛出 EntityExistsException。我使用 dto (CreateExamRequestDto) 获取 REST 请求，然后将此 dto 映射到实体并使用 Spring Data JPA 保存它。

这是我的实体类:

考试实体:

@Entity
@Table(name = "exams", uniqueConstraints = {@UniqueConstraint(columnNames = {
        "name",
        "category_id"
})})
public class Exam extends AbstractEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "exams_seq_gen")
    @SequenceGenerator(name = "exams_seq_gen", sequenceName = "exams_id_seq")
    @Column(name = "id")
    private Integer id;
    @Column(name = "name", nullable = false)
    private String name;
    @ManyToOne
    @JoinColumn(name = "category_id", nullable = false)
    private Category category;
    @ManyToOne
    @JoinColumn(name = "owner_id", nullable = false)
    private User owner;
    @OneToMany(cascade = {CascadeType.MERGE, CascadeType.PERSIST})
    private List<Section> sections;
    @Column(name = "target_score", nullable = false)
    private Integer targetScore;
    @OneToMany()
    private List<ExamResult> results;

    @Transient
    private ExamResult result;

    //public constructor, getters, setters, hashcode and equals
}

部分实体:

@Entity
@Table(name = "exam_sections", uniqueConstraints = @UniqueConstraint(columnNames = {
        "name",
        "exam_id"
}))
public class Section extends AbstractEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "exam_sections_seq_gen")
    @SequenceGenerator(name = "exam_sections_seq_gen", sequenceName = "exam_sections_id_seq")
    @Column(name = "id")
    private Integer id;
    @Column(name = "name", nullable = false)
    private String name;
    @Column(name = "question_weight", nullable = false)
    private Integer questionWeight;
    @Column(name = "target_questions", nullable = false)
    private Integer targetQuestions;
    @OneToMany(cascade = {CascadeType.MERGE, CascadeType.PERSIST})
    private List<Question> questions;
    @ManyToOne
    @JoinColumn(name = "exam_id", nullable = false)
    private Exam exam;

    //public constructor, getters, setters, hashcode and equals
}

问题实体:

@Entity
@Table(name = "questions")
public class Question extends AbstractEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "questions_seq_gen")
    @SequenceGenerator(name = "questions_seq_gen", sequenceName = "questions_id_seq")
    @Column(name = "id")
    private Integer id;
    @Column(name = "text", nullable = false)
    private String text;
    @Column(name = "type", nullable = false)
    @Enumerated(EnumType.STRING)
    private QuestionType type;
    @OneToMany(cascade = {CascadeType.MERGE, CascadeType.PERSIST})
    private List<Answer> answers;
    @ManyToOne
    @JoinColumn(name = "section_id")
    private Section section;

    //public constructor, getters, setters, hashcode and equals
}

回答实体:

@Entity
@Table(name = "answers")
public class Answer extends AbstractEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "answers_seq_gen")
    @SequenceGenerator(name = "answers_seq_gen", sequenceName = "answers_id_seq")
    @Column(name = "id")
    private Integer id;
    @Column(name = "text", nullable = false)
    private String text;
    @Column(name = "correct", nullable = false)
    private Boolean correct;
    @ManyToOne
    @JoinColumn(name = "question_id", nullable = false)
    private Question question;

    //public constructor, getters, setters, hashcode and equals
}

以及保存所有内容的代码:

@Override
@Transactional
public ExamShortDto createExam(CreateExamRequestDto request) {
    Exam exam = examMapper.mapToEntity(request, user);
    exam = examRepository.save(exam);             <<----- HERE

    return examMapper.mapToShortDto(exam);
}

在尖线上我遇到了下一个异常:

2017-09-05 17:24:12.278 ERROR 14024 --- [nio-8080-exec-1] o.s.b.w.servlet.support.ErrorPageFilter :由于异常，从请求 [/api/exam] 转发到错误页面 [具有相同标识符值的不同对象已与 session 关联:[org.yvasylchuk.testit.domain.entity.exam.Answer#191]；嵌套异常是 javax.persistence.EntityExistsException:具有相同标识符值的不同对象已与 session 关联:[org.yvasylchuk.testit.domain.entity.exam.Answer#191]]

org.springframework.dao.DataIntegrityViolationException: A different object with the same identifier value was already associated with the session : [org.yvasylchuk.testit.domain.entity.exam.Answer#191]; nested exception is javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [org.yvasylchuk.testit.domain.entity.exam.Answer#191]
    at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:395) ~[spring-orm-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:226) ~[spring-orm-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:499) ~[spring-orm-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:59) ~[spring-tx-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:216) ~[spring-tx-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:153) ~[spring-tx-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:134) ~[spring-data-jpa-2.0.0.RC2.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:61) ~[spring-data-commons-2.0.0.RC2.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.0.RC3.jar:5.0.0.RC3]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.0.0.RC3.jar:5.0.0.RC3]
    at com.sun.proxy.$Proxy130.save(Unknown Source) ~[na:na]
    at org.yvasylchuk.testit.service.exam.impl.ExamFacadeImpl.createExam(ExamFacadeImpl.java:143) ~[classes/:0.0.1-SNAPSHOT]

    ......

Caused by: javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [org.yvasylchuk.testit.domain.entity.exam.Answer#191]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:116) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:155) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:162) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:811) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:771) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:458) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:383) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:491) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:423) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:386) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:126) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:445) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:281) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:182) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:804) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:771) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:458) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:383) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:491) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:423) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:386) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:126) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:445) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:281) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:182) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:804) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:771) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:458) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:383) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:491) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:423) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:386) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:193) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:126) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:445) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:281) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:182) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:780) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:765) ~[hibernate-core-5.2.10.Final.jar:5.2.10.Final]
    ...

解决方案:

我只是将答案实体中的一行更改为:

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "answers_seq_gen")
HERE -->> @SequenceGenerator(name = "answers_seq_gen", sequenceName = "answers_id_seq")
@Column(name = "id")
private Integer id;

至:

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "answers_seq_gen")
HERE -->> @SequenceGenerator(name = "answers_seq_gen", sequenceName = "answers_id_seq", allocationSize = 200)
@Column(name = "id")
private Integer id;

Answer 1

实际发生的情况:由于您正在级联答案并且由于关系是 OneToMany，因此您可能有许多超过分配大小(序列生成器)的默认值的答案具有属性分配大小，指示交易中可能增量的数量，因此如果超出限制，您的 ID 中将出现重复。

解决方案:您可以将生成器更改为自动或增加分配大小