Question

我正在尝试获取所有用户对自定义问题中的邮件的投票：

List<Vote> list = sessionFactory.getCurrentSession()
        .createQuery("from Vote as v left join v.message as m " +
                "where m.question=:question and v.user=:user and v.voteType=:voteType")
        .setParameter("question", question)
        .setParameter("user", user)
        .setParameter("voteType", VoteType.MESSAGE)
        .list();
System.out.println(list.get(0).getMessage().getNumber());

在最后一个字符串中出现异常：

java.lang.ClassCastException：[Ljava.lang.Object;无法施展 ru.kapahgaiii.qa.domain.Vote ru.kapahgaiii.qa.repository.ChatDAOImpl.getVotes（ChatDAOImpl.java:114）

我做错了什么？

Vote.java：

@Entity
@Table(name = "votes")
public class Vote {

    @Id
    @GeneratedValue
    @Column(name = "vote_id")
    private Integer voteId;

    @ManyToOne
    @JoinColumn(name = "uid")
    private User user;

    @Column(name = "vote_type", length = 8)
    @Enumerated(EnumType.STRING)
    private VoteType voteType;

    @ManyToOne
    @JoinColumn(name = "message_id")
    private Message message;

Answer 1

你做错了演员。 Hibernate会根据您的请求返回查询中的所有对象。但是你需要使用Vote对象，它位于索引0。

List<Object[]> list = sessionFactory.getCurrentSession()
        .createQuery("from Vote as v left join v.message as m " +
                "where m.question=:question and v.user=:user and v.voteType=:voteType")
        .setParameter("question", question)
        .setParameter("user", user)
        .setParameter("voteType", VoteType.MESSAGE)
        .list();
System.out.println(list.get(0)[0].getMessage().getNumber());

Answer 2

尝试这样做：

List<Object> list = sessionFactory.getCurrentSession()
            .createQuery("from Vote as v left join v.message as m " +
                    "where m.question=:question and v.user=:user and v.voteType=:voteType")
            .setParameter("question", question)
            .setParameter("user", user)
            .setParameter("voteType", VoteType.MESSAGE)
            .list();
    System.out.println(((Vote) list.get(0)).getMessage().getNumber())

java.lang.Object无法强制转换

2 个答案: