在 JPA 中，将 @ManyToOne 作为 @Id 会在执行 em.getReference() 时引发 ClassCastException
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【中文标题】在 JPA 中，将 @ManyToOne 作为 @Id 会在执行 em.getReference() 时引发 ClassCastException【英文标题】：In JPA, having a @ManyToOne as @Id throws ClassCastException when doing em.getReference() 【发布时间】：2016-06-06 13:54:17 【问题描述】：我有这个导致以下异常的简单代码，可能是什么问题？？
MenuPK menuPK = new MenuPK(aVenueId, aMenuId);
Menu menu = em.getReference(Menu.class, menuPK); // where em is an EntityManager
//Menu menu = em.find(Menu.class, menuPK); // this works fine!!
// full trace
Exception Description: An internal error occurred accessing the primary key object [MenuPK@3ffa].
Internal Exception: java.lang.ClassCastException: java.lang.Long cannot be cast to Venue
Descriptor: RelationalDescriptor(Menu --> [DatabaseTable(Menus)])
VenuesWSrvc.deleteMenu(VenuesWSrvc.java:273)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4695)
com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:630)
com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:46)
sun.reflect.GeneratedMethodAccessor75.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4667)
com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4655)
com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
com.sun.proxy.$Proxy230.deleteMenu(Unknown Source)
WebServiceFilter.doFilter(WebServiceFilter.java:139)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
WebAuthFilter.doFilter(WebAuthFilter.java:186)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:316)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
org.glassfish.grizzly.strategies.Abstractiostrategy.fireIOEvent(AbstractIOStrategy.java:113)
org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
java.lang.Thread.run(Thread.java:745)
-----
java.lang.ClassCastException: java.lang.Long cannot be cast to Venue
VenuesWSrvc.deleteMenu(VenuesWSrvc.java:273)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4695)
com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:630)
com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:46)
sun.reflect.GeneratedMethodAccessor75.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4667)
com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4655)
com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
com.sun.proxy.$Proxy230.deleteMenu(Unknown Source)
WebServiceFilter.doFilter(WebServiceFilter.java:139)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
WebAuthFilter.doFilter(WebAuthFilter.java:186)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:316)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
java.lang.Thread.run(Thread.java:745)
-----
, 1, Failed to retrieve Menus, 1465220776471, /ws/deleteMenu, 3]
2016-06-06T16:46:16.477+0300|Fine: SELECT LAST_INSERT_ID()
2016-06-06T16:46:16.503+0300|Severe: javax.servlet.ServletException: Error invoking WebService: 'deleteMenu'
at WebServiceFilter.doFilter(WebServiceFilter.java:276)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
at WebAuthFilter.doFilter(WebAuthFilter.java:186)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:316)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Thread.java:745)
Caused by: ServiceException: Exception [EclipseLink-202] (Eclipse Persistence Services - 2.6.3.v20160428-59c81c5): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: An internal error occurred accessing the primary key object [MenuPK@3ffa].
Internal Exception: java.lang.ClassCastException: java.lang.Long cannot be cast to Venue
Descriptor: RelationalDescriptor(Menu --> [DatabaseTable(Menus)])
at VenuesWSrvc.deleteMenu(VenuesWSrvc.java:273)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4695)
at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:630)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:46)
at sun.reflect.GeneratedMethodAccessor75.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4667)
at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4655)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
at com.sun.proxy.$Proxy230.deleteMenu(Unknown Source)
at WebServiceFilter.doFilter(WebServiceFilter.java:139)
... 31 more
Caused by: Exception [EclipseLink-202] (Eclipse Persistence Services - 2.6.3.v20160428-59c81c5): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: An internal error occurred accessing the primary key object [MenuPK@3ffa].
Internal Exception: java.lang.ClassCastException: java.lang.Long cannot be cast to Venue
Descriptor: RelationalDescriptor(Menu --> [DatabaseTable(Menus)])
at org.eclipse.persistence.exceptions.DescriptorException.errorUsingPrimaryKey(DescriptorException.java:1937)
at org.eclipse.persistence.internal.jpa.CMP3Policy.createBeanUsingKey(CMP3Policy.java:342)
at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.getReference(UnitOfWorkImpl.java:5909)
at org.eclipse.persistence.internal.jpa.EntityManagerImpl.getReference(EntityManagerImpl.java:1405)
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.getReference(EntityManagerWrapper.java:418)
at VenuesWSrvc.deleteMenu(VenuesWSrvc.java:263)
... 62 more
Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to Venue
at Menu._persistence_set(Menu.java)
at org.eclipse.persistence.internal.descriptors.PersistenceObjectAttributeAccessor.setAttributeValueInObject(PersistenceObjectAttributeAccessor.java:102)
at org.eclipse.persistence.mappings.DatabaseMapping.setAttributeValueInObject(DatabaseMapping.java:1652)
at org.eclipse.persistence.internal.indirection.IndirectionPolicy.setRealAttributeValueInObject(IndirectionPolicy.java:340)
at org.eclipse.persistence.mappings.ForeignReferenceMapping.setRealAttributeValueInObject(ForeignReferenceMapping.java:1683)
at org.eclipse.persistence.internal.jpa.CMP3Policy.creat
2016-06-06T16:46:16.503+0300|Severe: eBeanUsingKey(CMP3Policy.java:338)
... 66 more
这是我的场地实体
@Entity
@Table(name="Venues")
public class Venue implements Serializable
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "id")
private long venueId;
@OneToMany(mappedBy="venue")
private List<Menu> menus;
还有一个代表场地可能有的菜单
@Entity
@Table(name="Menus")
@IdClass(MenuPK.class)
public class Menu implements Serializable
private static final long serialVersionUID = 1L;
@Id
@ManyToOne
@JoinColumn(name="venueId")
private Venue venue;
@Id
@Min(value=1)
private short menuId;
这是Menus的PK类
public class MenuPK implements Serializable
private static final long serialVersionUID = 1L;
private long venue;
private short menuId;
public MenuPK()
public MenuPK(long venueId, short menuId)
this.venue = venueId;
this.menuId = menuId;
public long getVenue()
return this.venue;
public short getMenuId()
return this.menuId;
public boolean equals(Object other)
if (this == other)
return true;
if (!(other instanceof MenuPK))
return false;
MenuPK castOther = (MenuPK)other;
return
(this.venue == castOther.venue) &&
(this.menuId == castOther.menuId);
public int hashCode()
final int prime = 31;
int hash = 17;
hash = hash * prime + (int)(this.venue ^ (this.venue >>> 32)); // taken from the hashCode() implementation of java.lang.Long
hash = hash * prime + ((int) this.menuId);
return hash;
【问题讨论】：
【参考方案1】：实体Menu的主键类型有：
长场地 短菜单 ID代表主键的类的类型有：
场地场地 短菜单 ID这就是为什么当您尝试获取具有 PK 的实体时会收到 ClassCastException 的原因
【讨论】：
这是一个@ManyToOne @Id。根据 JPA 规范，MenuPK 类中venue 的数据类型必须与 Venue 类中@Id 字段的数据类型匹配（并且不是 Venue 本身的类型）。请注意，上面的代码适用于 em.find() 而不是 em.getReference，两者都使用 MenuPK 类。以上是关于在 JPA 中，将 @ManyToOne 作为 @Id 会在执行 em.getReference() 时引发 ClassCastException的主要内容，如果未能解决你的问题，请参考以下文章
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