在Java EE中使用JPA建模表关系

Question

我的数据库中有两个3表：

group
----------
groupId    PK
name

user_account
----------
userId        PK

user_grouping
----------
groupId     PK    FK grouping(groupId -> groupId)
userId      PK    FK user_account(userId -> userId)

在我的UserAccount实体中，我有以下行：

@JoinTable(name = "user_group", joinColumns = {
    @JoinColumn(name = "userId", referencedColumnName = "userId")}, inverseJoinColumns = {
    @JoinColumn(name = "groupId", referencedColumnName = "groupId")})
@ManyToMany
private List<Grouping> groupingList;

这是为了显示所有表之间的关系。但是，当我部署时，我得到以下错误：

SEVERE: Exception while preparing the app : Exception [EclipseLink-28018] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Predeployment of PersistenceUnit [com.dv_model_ejb_1.0-SNAPSHOTPU] failed.
Internal Exception: Exception [EclipseLink-7220] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The @JoinColumns on the annotated element [field groupingList] from the entity class [class com.dv.model.entity.UserAccount] is incomplete. When the source entity class uses a composite primary key, a @JoinColumn must be specified for each join column using the @JoinColumns. Both the name and the referencedColumnName elements must be specified in each such @JoinColumn.
Local Exception Stack: 
Exception [EclipseLink-28018] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Predeployment of PersistenceUnit [com.dv_model_ejb_1.0-SNAPSHOTPU] failed.
Internal Exception: Exception [EclipseLink-7220] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The @JoinColumns on the annotated element [field groupingList] from the entity class [class com.dv.model.entity.UserAccount] is incomplete. When the source entity class uses a composite primary key, a @JoinColumn must be specified for each join column using the @JoinColumns. Both the name and the referencedColumnName elements must be specified in each such @JoinColumn.
    at org.eclipse.persistence.exceptions.EntityManagerSetupException.predeployFailed(EntityManagerSetupException.java:221)
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:1402)
...

我不确定如何准确解释此错误消息。我假设在实体中没有正确建模表关系。但我不知道为什么。在今天之前，这是很好的编译。有人能提供帮助吗？

Answer 1

表的描述不一致（分组与组），实体映射中联接表的名称不是表名称之一。由于这些不一致，我假设以下表格结构：

useraccount (userid PK)
grouping (groupdid PK, name)
user_grouping (userId PK, groupId PK)
- FK userId references to user_account.userid
- FK groupId references to grouping.groupId

将其映射到两个实体的正确方法如下：

@Entity
public class UserAccount {
    @Id int userId;

    @JoinTable(name = "user_grouping", joinColumns = {
       @JoinColumn(name = "userId", referencedColumnName = "userId")},
       inverseJoinColumns = {
       @JoinColumn(name = "groupId", referencedColumnName = "groupId")})
       @ManyToMany
       private List<Grouping> groupingList;
    //get and set omitted.
}

@Entity
public class Grouping {
    @Id int groupId;
    String name;
    //get,set, and optional inverse side of relationship omitted
}