java - EJB QL 语法错误

Question

在我的应用程序中，我有以下 2 个实体:

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Commentable implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    protected Long id;
    protected long createdDate;
    ...
}

@Entity
public class Announcement extends Commentable implements Serializable { 

    private int    type;  
    private String title;
    @Column(columnDefinition = "MEDIUMTEXT")
    private String content;
    ...
}

当我尝试从公告表中获取某些行时，我不断在以下行中收到语法错误:

Query q = em.createQuery("SELECT A FROM Announcement A JOIN Commentable C ON A.id = C.id WHERE A.type=:type ORDER BY C.createdDate DESC");

这是堆栈跟踪:

Caused by: Exception [EclipseLink-8023] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.JPQLException
Exception Description: Syntax error parsing the query [SELECT A FROM Announcement A JOIN Commentable C ON A.id = C.id WHERE A.type=:type ORDER BY C.createdDate DESC].
Internal Exception: org.eclipse.persistence.internal.libraries.antlr.runtime.EarlyExitException

如果您能告诉我我在这里做错了什么，我将非常感激。

最诚挚的问候， 詹姆斯·特兰

Answer 1

如果“公告”扩展了“可评论”，则不需要加入:

select a from Announcement a where a.type = :type order by a.createdDate desc