JPA 2.1 ConstructorResult导致ClassCastException

Question

我的结果集中的对象被强制转换为＆＃39;对象＆＃39;而不是我在@SQLResultSetMapping对象中指定的内容。

我试图获取ConstructorResult的句柄，并创建了一个包含简单连接的查询，并尝试获取结果集并循环，但是将其打印出来以确保我正确。然而，当我进入循环时，看起来它应该是直截了当的不是。

当我声明结果列表时，它被转换为类型。我逐步完成查询测试类，它成功运行查询并将其加载到结果中，但结果列表中的项目已键入为＆＃39;对象＆＃39;而不是CommentInfoListItemDTO对象。因此，当我进入循环时，它会遇到类强制转换异常。为什么不将结果强制转换为CommentInfoListItemDTO对象？特别是在@SQLResultSetMapping中具体说明时。

代码发布在下面......我截断了一些列名，只是为了缩短它们。如果它有助于将其添加回来让我知道。

public List<CommentInfoListItemDTO> getCommentTitleListByPersonId(BigInteger personId) {
    String queryString = "select c.article_id, "
                        ***[columns removed for brevity]***
                        + "c.person_id as comment_person_id, "
                        + "a.party_id as aticle_party_id "
                        + "from article_comment c "
                        + "join article a "
                        + "on a.article_id = c.article_id "
                        + "where c.person_id = :personId";

    Query q = em.createNativeQuery(queryString, "CommentInfoListItemDTOMapping");
    q.setParameter("personId", personId);

    List<CommentInfoListItemDTO> commentInfoList = q.getResultList();

    ***[throws exception on the next line]***
    ***[java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com...CommentInfoListItemDTO]***

    for (CommentInfoListItemDTO listElement : commentInfoList){
            System.out.println("COMMENT TITLE LIST: " + listElement.toString());
        }
    return (commentInfoList);
}

@SqlResultSetMapping -

已编辑 - 显示如何将其放置在现有实体类中。

已编辑 - 我尝试将数据类型添加到映射中的列列表中。它没有任何帮助。结果集中的每条记录仍然被转换为Hibernate内部的java.lang.Object，它不会让我把它转回DTO。结果集映射受Hibernate约束：

  

INFO：绑定结果集映射：CommentInfoListItemDTOMapping

@Entity
@SqlResultSetMapping(name = "CommentInfoListItemDTOMapping", classes = {
    @ConstructorResult(targetClass = CommentInfoListItemDTO.class,
            columns = {
            @ColumnResult(name = "article_id", type=BigInteger.class),
            @ColumnResult(name = "article_comment_id", type=BigInteger.class),
            @ColumnResult(name = "parent_comment_id", type=BigInteger.class),
            @ColumnResult(name = "article_title", type=String.class),
            @ColumnResult(name = "article_published", type=Boolean.class),
            @ColumnResult(name = "article_publish_date", type=Calendar.class),
            @ColumnResult(name = "article_availability_state", type=String.class),
            @ColumnResult(name = "article_enable_comments", type=Boolean.class),
            @ColumnResult(name = "comment_title", type=String.class),
            @ColumnResult(name = "comment_hide", type=Boolean.class),
            @ColumnResult(name = "comment_created_timestamp", type=Calendar.class),
            @ColumnResult(name = "comment_person_id", type=BigInteger.class),
            @ColumnResult(name = "aticle_party_id", type=BigInteger.class)
            })
})

@Table(name = "article_comment")
@NamedQueries({
    @NamedQuery(name = "ArticleComment.findAll", query = "SELECT e FROM ArticleComment e")})

public class ArticleComment implements Serializable {
...

POJO

public class CommentInfoListItemDTO implements Serializable {

    private Integer id;
    private BigInteger articleId;
    private BigInteger articleCommentId;
    private BigInteger parentCommentId;
    private String articleTitle;
    private Boolean articlePublished;
    @Temporal(javax.persistence.TemporalType.DATE)
    private Calendar articlePublishDate;
    private String articleAvailabilityState;
    private Boolean articleEnableComments;
    private String commentTitle;
    private Boolean commentHide;
    @Temporal(javax.persistence.TemporalType.DATE)
    private Calendar commentCreatedTimestamp;
    private BigInteger commentPersonId;
    private BigInteger articlePartyId;

    public CommentInfoListItemDTO() {
    }

    public CommentInfoListItemDTO(BigInteger articleId, BigInteger articleCommentId, 
            BigInteger parentCommentId, String articleTitle, Boolean articlePublished, 
            Calendar articlePublishDate, String articleAvailabilityState, 
            Boolean articleEnableComments, String commentTitle, Boolean commentHide, 
            Calendar commentCreatedTimestamp, BigInteger commentPersonId, 
            BigInteger articlePartyId) {
        this.articleId = articleId;
        this.articleCommentId = articleCommentId;
        this.parentCommentId = parentCommentId;
        this.articleTitle = articleTitle;
        this.articlePublished = articlePublished;
        this.articlePublishDate = articlePublishDate;
        this.articleAvailabilityState = articleAvailabilityState;
        this.articleEnableComments = articleEnableComments;
        this.commentTitle = commentTitle;
        this.commentHide = commentHide;
        this.commentCreatedTimestamp = commentCreatedTimestamp;
        this.commentPersonId = commentPersonId;
        this.articlePartyId = articlePartyId;
    }

最后一个来自调试器的screengrab将结果集显示为Objects而不是CommentInfoListItemDTO对象。然而，正确的信息在对象中。

Answer 1

  

java.lang.ClassCastException：[Ljava.lang.Object;无法投射到YourDTO

当EclipseLink找不到传递给

的YourDTO名称时，会抛出

em.createNativeQuery("SELECT...","YourDTO");

Hibernate在类似情况下引发的异常是：

org.hibernate.MappingException: Unknown SqlResultSetMapping [someNonExistingMappingName]

您必须确保持久性提供商注册YourDTO。如何？观察您的日志：

休眠：

  

DEBUG annotations.ResultsetMappingSecondPass - 绑定结果集映射：YourDTO

的EclipseLink： 我没有找到任何日志。

对您的地图进行另外一次评论：将@ColumnResult与type一起用于不明确的类型：

@ColumnResult(name = "article_publish_date", type=Calendar.class)
@ColumnResult(name = "article_id", type=BigInteger.class)