java - 如果 Hibernate 已经存在，为什么要插入具有相同键的新实体？

Question

我遇到以下问题。我已将示例插入 GitHub 中。

如果我想保留我的类PlayerStatistics的实例，那么Hibernate会尝试创建一个已经存在的Matchday实体(指定为@ManyToOne)，我不想这样做，但我似乎无法绕过它。

我坚持使用 DemoApplicationTests 的 init 方法。

@Before
public void init() {
    final Matchday matchday = matchdayRepository.save(new Matchday(1));
    final Club club1 = clubRepository.save(new Club("Klub1"));
    final Club club2 = clubRepository.save(new Club("Klub2"));
    final Match match = matchRepository.save(new Match(matchday, club1, club2));
    final Player player = playerRepository.save(new Player(1, "Jan", "Kowalski", club1)); 
    playerStatisticsRepository.save(new PlayerStatistics(matchday, player, match));
}

如果我有上面的情况，那么我会得到以下异常。

org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [SYS_PK_10114]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:278)
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:244)
    at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:521)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:761)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:730)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:504)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:292)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
    at com.sun.proxy.$Proxy102.save(Unknown Source)
    at com.example.DemoApplicationTests.init(DemoApplicationTests.java:49)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
    at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:59)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:97)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:207)
    at org.hibernate.engine.jdbc.batch.internal.NonBatchingBatch.addToBatch(NonBatchingBatch.java:45)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2934)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3434)
    at org.hibernate.action.internal.EntityInsertAction.execute(EntityInsertAction.java:89)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:582)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:456)
    at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:337)
    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:39)
    at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1407)
    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:477)
    at org.hibernate.internal.SessionImpl.flushBeforeTransactionCompletion(SessionImpl.java:3170)
    at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2384)
    at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:467)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:146)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access$100(JdbcResourceLocalTransactionCoordinatorImpl.java:38)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:220)
    at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:68)
    at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:517)
    ... 44 more
Caused by: java.sql.SQLIntegrityConstraintViolationException: integrity constraint violation: unique constraint or index violation; SYS_PK_10114 table: MATCHDAY
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
    at org.hsqldb.jdbc.JDBCPreparedStatement.fetchResult(Unknown Source)
    at org.hsqldb.jdbc.JDBCPreparedStatement.executeUpdate(Unknown Source)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:204)
    ... 62 more
Caused by: org.hsqldb.HsqlException: integrity constraint violation: unique constraint or index violation; SYS_PK_10114 table: MATCHDAY
    at org.hsqldb.error.Error.error(Unknown Source)
    at org.hsqldb.Constraint.getException(Unknown Source)
    at org.hsqldb.index.IndexAVLMemory.insert(Unknown Source)
    at org.hsqldb.persist.RowStoreAVL.indexRow(Unknown Source)
    at org.hsqldb.TransactionManager2PL.addInsertAction(Unknown Source)
    at org.hsqldb.Session.addInsertAction(Unknown Source)
    at org.hsqldb.Table.insertSingleRow(Unknown Source)
    at org.hsqldb.StatementDML.insertSingleRow(Unknown Source)
    at org.hsqldb.StatementInsert.getResult(Unknown Source)
    at org.hsqldb.StatementDMQL.execute(Unknown Source)
    at org.hsqldb.Session.executeCompiledStatement(Unknown Source)
    at org.hsqldb.Session.execute(Unknown Source)
    ... 65 more

如果我调试 HQL，我可以清楚地看到 Hibernate 想要在表 Matchday 中插入一个新行，即使它已经存在。

Hibernate: 
    insert 
    into
        Matchday
        (matchdayNumber) 
    values
        (?)

如果我注释 init() 方法的最后一行，那么它工作正常，所以问题必须出在这部分:playerStatisticsRepository.save(new PlayerStatistics(matchday, player, match))

@Before
public void init() {
    final Matchday matchday = matchdayRepository.save(new Matchday(1));
    final Club club1 = clubRepository.save(new Club("Klub1"));
    final Club club2 = clubRepository.save(new Club("Klub2"));
    final Match match = matchRepository.save(new Match(matchday, club1, club2));
    final Player player = playerRepository.save(new Player(1, "Jan", "Kowalski", club1)); 
    //playerStatisticsRepository.save(new PlayerStatistics(matchday, player, match));
}

我在这里做错了什么？

PlayerStatistics 类看起来像这样。

@Entity
@IdClass(PlayerStatisticsId.class)
public class PlayerStatistics implements Serializable {
    //...
    @Id
    @ManyToOne(optional = false)
    @PrimaryKeyJoinColumn
    private Player player;

    @Id
    @ManyToOne(optional = false)
    @PrimaryKeyJoinColumn
    private Matchday matchday;

    @ManyToOne(optional = false)
    @JoinColumns({ @JoinColumn(name = "matchday_matchdaynumber", referencedColumnName = "matchday_matchdaynumber"),
            @JoinColumn(name = "hometeam_name", referencedColumnName = "hometeam_name") })
    private Match match;

    @Column(nullable = false)
    private boolean playedFromTheFirstWhistleblow;

    @Min(0)
    @Column(nullable = false)
    private int enteredTheFieldAtInSeconds;

    @Min(0)
    @Column(nullable = false)
    private int leftTheFieldAtInSeconds;

    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable
    @MapKeyEnumerated(EnumType.STRING)
    private Map<ScoreType, Integer> statistics = new HashMap<>();

    //...
}

编辑

如果我想直接从 Player 实体管理它。然后我收到一个异常，该实体已经与 session 关联，但它似乎并未关联。

@Before
public void init() {
    final Matchday matchday = matchdayRepository.save(new Matchday(1));
    final Club club1 = clubRepository.save(new Club("Klub1"));
    final Club club2 = clubRepository.save(new Club("Klub2"));
    final Match match = matchRepository.save(new Match(matchday, club1, club2));
    final Player player = new Player(1, "Jan", "Kowalski", club1);
    player.addPlayerStatistics(new PlayerStatistics(matchday, player, match));
    playerRepository.save(player);
}

org.springframework.dao.DataIntegrityViolationException: A different object with the same identifier value was already associated with the session : [com.example.model.Player#1]; nested exception is javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [com.example.model.Player#1]
    at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:410)
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:246)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:491)
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:59)
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:213)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:147)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
    at com.sun.proxy.$Proxy99.save(Unknown Source)
    at com.example.DemoApplicationTests.init(DemoApplicationTests.java:49)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [com.example.model.Player#1]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:116)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:155)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:162)
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:899)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:855)
    at org.hibernate.engine.spi.CascadingActions$6.cascade(CascadingActions.java:261)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:391)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:316)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:155)
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:424)
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:356)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:319)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:155)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:104)
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:445)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:238)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:300)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:169)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:68)
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:864)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:845)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:850)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:298)
    at com.sun.proxy.$Proxy97.merge(Unknown Source)
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:509)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:503)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:488)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:460)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136)
    ... 37 more

Answer 1

这里的问题在于 PlayerStatisticsId 及其定义方式。

原来是这样的。

public class PlayerStatisticsId implements Serializable {
    //..
    private long player;

    private int matchday;

    public long getPlayer() {
        return player;
    }

    public int getMatchday() {
        return matchday;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof PlayerStatisticsId) {
            final PlayerStatisticsId o = (PlayerStatisticsId) obj;
            return o.matchday == matchday && o.player == player;
        } else {
            return false;
        }
    }
}

我可以发誓我在某处读到只有基元/基本类型可以在用于 @ClassId 的类中使用。但事实似乎并非如此。

修改后

public class PlayerStatisticsId implements Serializable {
    //...

    private Player player;

    private Matchday matchday;

    public Player getPlayer() {
        return player;
    }

    public Matchday getMatchday() {
        return matchday;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof PlayerStatisticsId) {
            final PlayerStatisticsId o = (PlayerStatisticsId) obj;
            return o.matchday.equals(matchday) && o.player.equals(player);
        } else {
            return false;
        }
    }
}

看起来确实有效。我现在收到一个完全不同的异常，但这是一个单独问题的情况。