JPA映射：外键在引用的主键中必须具有相同的列数

Question

我使用的是JPA 2.0与Hibernate 4.1.0.Final。我无法弄清楚如何映射几个实体。我有一组和GroupMember类，但以下的映射......

@Entity 
@Table(name = "group") 
public class Group  
{ 
    @Id 
    @NotNull 
    @GeneratedValue(generator = "uuid-strategy") 
    @Column(name = "ID") 
    private String id; 
    … 

    @ManyToMany 
    @ElementCollection 
    @CollectionTable(name="group_member", joinColumns=@JoinColumn(name="GROUP_ID")) 
    private Set<GroupMember> members; 




@Entity 
@Table(name = "group_member") 
public class GroupMember 
{ 

    @Id 
    @NotNull 
    @GeneratedValue(generator = "uuid-strategy") 
    @Column(name = "ID") 
    private String id; 
    … 

    @ManyToOne 
    @JoinColumn(name = "GROUP_ID", nullable = false, updatable = true) 
    private Group group; 

结果在这个异常...

Caused by: javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build EntityManagerFactory 
    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:914) 
    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:889) 
    at org.hibernate.ejb.HibernatePersistence.createContainerEntityManagerFactory(HibernatePersistence.java:73) 
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:287) 
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:310) 
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1514) 
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1452) 
    ... 38 more 
Caused by: org.hibernate.MappingException: Foreign key (FK4719AC489E4DD84:group_member [members_ID])) must have same number of columns as the referenced primary key (group_member [GROUP_ID,members_ID]) 
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:110) 
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:93) 
    at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1704) 
    at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1627) 
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1362) 
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1727) 
    at org.hibernate.ejb.EntityManagerFactoryImpl.<init>(EntityManagerFactoryImpl.java:88) 
    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:904) 

如何将我的GroupMembers字段映射到我的小组课吗？

... 44 more 

Answer 1

问题是你有一个@OneToMany和@ManyToMany在另一边。此外@ElementCollection和@CollectionTable在这种情况下，错误的注释为您正在处理的实体的集合，而不是Embeddables：

​​

如果模型是这样的，一个组可以有许多成员和会员可以属于很多组，那么你有两个选择。您可以使用@ManyToMany Group <> Member（并使用@JoinTable定义Join表），或者，您可以为联接定义一个中间实体并将关系映射为@OneToMany。

后者是推荐的方法，因为它允许您存储关于关系的额外信息：例如，在这种情况下，您可以在GroupMember上定义一个额外字段来存储成员加入该组的日期。

@Entity 
@Table(name = "group") 
public class Group  
{ 
    @Id 
    @NotNull 
    @GeneratedValue(generator = "uuid-strategy") 
    @Column(name = "ID") 
    private String id; 
    … 

    @OneToMany(mappedBy = "group") 
    private Set<GroupMember> members; 
} 

@Entity 
@Table(name = "member") 
public class Member  
{ 
    @Id 
    @NotNull 
    @GeneratedValue(generator = "uuid-strategy") 
    @Column(name = "ID") 
    private String id; 
    … 

    @OneToMany(mappedBy = "member") 
    private Set<GroupMember> groups; 
} 

@Entity 
@Table(name = "group_member") 
public class GroupMember 
{ 

    @Id 
    @NotNull 
    @GeneratedValue(generator = "uuid-strategy") 
    @Column(name = "ID") 
    private String id; 
    … 

    @ManyToOne 
    @JoinColumn(name = "GROUP_ID", nullable = false, updatable = true) 
    private Group group; 

    @ManyToOne 
    @JoinColumn(name = "MEMBER_ID", nullable = false, updatable = true) 
    private Member member; 
}