从休眠获取数据时发生java.lang.ClassCastException

Question

I am trying to print details of fetched data using HQL query as follow

List list = sess.createQuery("from PostMessages as pm "
                    + " left join pm.postImageses as pi "
                    + " left join pm.videosDescriptions as vd "
                    + "where pm.messageid=:msgId")
                       .setParameter("msgId", msgId).list();

            List<PostMessages> result = (List<PostMessages>) list;
            Iterator itr = result.iterator();
            while (itr.hasNext()) {
                PostMessages pm = (PostMessages) itr.next();
                System.out.print("msg: " + pm.getMessage());
                System.out.print(" type: " + pm.getMessageType());
                Set images = pm.getPostImageses();
                Iterator itr1 = images.iterator();
                while (itr1.hasNext()) {
                    PostImages pi = (PostImages) itr1.next();
                    System.out.print("id: " + pi.getImageId());
                    System.out.print("desc: " + pi.getImgDesc());
                }
                Set videos = pm.getVideosDescriptions();
                Iterator itr2 = videos.iterator();
                while (itr2.hasNext()) {
                    VideosDescription vd = (VideosDescription) itr1.next();
                    System.out.print("id: " + vd.getVideoId());
                    System.out.print("desc: " + vd.getDescription());
                }
            }

But this is showing following exception

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to 
hibernetMappings.PostMessages
    at hibernetMappings.TestPost.main(TestPost.java:40)

How to resolve this exception.

Answer 1

Add a select clause to your query:

select distinct pm from PostMessages as pm ...

Note that the left joins are useless. If the goal is to retrieve the post messages with their images and video descriptions in a single query, you should use left join fetch .

You should also use an Iterator<PostMessages> , instead of a raw Iterator. And the entity should be named PostMessage , and not PostMessages : each instance is one message, not several. getImageses() should be getImages() .

Answer 2

Try to do this.

  Iterator itr = result.iterator();

to

  Iterator<PostMessages> itr = result.iterator();

Also change

List<PostMessages> list = sess.createQuery("from PostMessages as pm "
                    + " left join fetch pm.postImageses as pi "
                    + " left join fetch pm.videosDescriptions as vd "
                    + "where pm.messageid=:msgId")
                       .setParameter("msgId", msgId).list();