Hibernate Projections List

Question

I ned to get only a few column values from the table. So I have used Projections to achieve this. The code works, but I don't think it is effective.

My issue was when I used ProjectionsList & then set the criteria.list to an ArrayList - the Bulletin object is null. I'm not sure how to explain this better. So I will put the code and then please read below:

 List<Bulletin> list = new ArrayList<Bulletin>();
 BulletinList bulletinList = null;

 Criteria criteria = null;

 criteria = this.getSession().createCriteria(Bulletin.class)
            .setProjection(Projections.projectionList()
            .add(Projections.property(bulletinIdAttr))
            .add(Projections.property(docNameAttr))   
            .add(Projections.property(docTypeCodeAttr))
            );        
    criteria.addOrder(Order.desc(createdTimeAttr));

    List<Object> rows = criteria.list();
    for (Object r : rows) {
        Object[] row = (Object[]) r;
        Bulletin bull = new Bulletin();
        bull.setBulletinId((Long) row[0]);
        bull.setDocumentName((String) row[1]);
        bull.setDocumentTypeCode((String) row[2]);
        list.add(bull);
      }

    bulletinList = new BulletinList();
    bulletinList.setBulletins(list);

    return bulletinList;

I just need to set criteria.list to BulletinList (Class that holds a list of Bulletin objects). But when I use projections, Bulletin object is null.

I also was reading another thread to use

setResultTransformer(Transformers.aliasToBean

But that ain't working either. So can someone help in this on how to make the code better.

Thanks

Harish

Answer 1

1. Projections.property() takes a String as an argument. In the code you provided the value of that String should be the name of a member of the Bulletin class. Presumably bulletinIdAttr, for example, is a String with such a value otherwise you would be getting runtime errors.

2. When you call setProjection on a Criteria instance you are implicitly setting the ResultTransformer to PROJECTIONS and this is what you want. No need to call setResultTransformer yourself. I would simplify the routine a little like this

   List<Object[]> rows = criteria.list();
   for (Object[] row : rows) {
      Bulletin bull = new Bulletin();
      bull.setBulletinId((Long) row[0]);
      bull.setDocumentName((String) row[1]);
      bull.setDocumentTypeCode((String) row[2]);
      list.add(bull);
   }
   

But that shouldn't make any difference to your results. Have you checked that rows is empty?