java.lang.Object cannot be cast

Question

I'm trying to get all user votes for messages in custom question:

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());

And got exception in the last string:

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to ru.kapahgaiii.qa.domain.Vote ru.kapahgaiii.qa.repository.ChatDAOImpl.getVotes(ChatDAOImpl.java:114)

What am I doing wrong?

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;

Can you check with a debugger if list really contains Vote objects? — Wim Deblauwe
– Wim Deblauwe, Commented Jan 17, 2015 at 12:36

Roman C · Accepted Answer · 2015-01-17 12:46:29Z

3

You are doing wrong cast. Hibernate returns you all objects from the query as you requested. But you needed to use Vote object, which is at index 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());

edited Jan 17, 2015 at 12:46

answered Jan 17, 2015 at 12:40

Roman C

1

Sign up to request clarification or add additional context in comments.

3 Comments

Marko Topolnik Over a year ago

OP, it would at least be interesting to find out what object is at index 1. Your query clearly asks for just one item per row so my guess is that you have not posted the real query you are executing.

Erwin Bolwidt Over a year ago

@MarkoTopolnik That would probably be a string containing v.message. The OP should use select v from Vote as v left join ... if he just wants to get Vote objects in the list.

Marko Topolnik Over a year ago

@ErwinBolwidt Yes, that's the only explanation I could come up with and if it is correct, then your suggestion is clearly what OP should have done instead of this workaround. However, aren't the join semantics such that they just result in an eagerly loaded message field? Quote:

The associated objects are also not returned directly in the query results. Instead, they may be accessed via the parent object.

But this applies to fetch joins, so that may be the key difference. Hibernate's docs are generally quite hazy about these semantics, often it takes trial an error to second-guess them.

celezar · Accepted Answer · 2015-01-17 12:51:26Z

-1

Try doing it like this:

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())

;

answered Jan 17, 2015 at 12:51

celezar

4423 silver badges9 bronze badges

1 Comment

Marko Topolnik Over a year ago

This is what OP is doing, only implicitly. It will fail with the same error.

Collectives™ on Stack Overflow

java.lang.Object cannot be cast

2 Answers 2

3 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related