Spring Jpa共享主键

Question

我希望我的Account表中的User共享主键。所以我这样做了：

@Entity
@Table(name = "user")
public class User implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "user_id")
    private int userId;

    @OneToOne(mappedBy = "user", cascade = CascadeType.ALL)
    private Account account;
}

@Entity
@Table(name = "account")
public class Account implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "user_id")
    private int userId;

    private String password;

    private String username;

    // bi-directional one-to-one association to User
    @OneToOne
    @JoinColumn(name = "user_id")
    @MapsId
    private User user;
}

以下是保存新帐户时的代码。

User user= userService.get(1);
Account account = new Account();
account.username("Loi");
account.password("mypass");

contact.setAccount(account);
account.setUser(contact);

accountService.save(account);

然后我得到了这个例外

org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist: com.amashub.tc.models.User; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: com.amashub.tc.models.User
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:276)
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:221)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:417)
    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$CrudMethodMetadataPopulatingMethodIntercceptor.invoke(CrudMethodMetadataPostProcessor.java:122)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
    at com.sun.proxy.$Proxy65.save(Unknown Source)

我在哪里错过了？