Pagination with Hibernate Criteria and DISTINCT_ROOT_ENTITY

Question

I\'ve have already implemented pagination using the following code:

public Paginacao consultarPaginado(int pagina, Integer cidadeId) {

               


        

Answer 1

This was an issue for me, and it took some time to come up with a solution that works for all the scenarios I have.

What you want for each pagination page is 2 things, the total count of all results and your single page of results, but to do that you need to take 3 steps. 1) get the total count, 2) get the unique ids for your page, and 3) get the full data for the ids found in step 2. And you can do all that with a single criteria object:

1) get total count, using distinct ids (uniqueField = the name of your id in the entity class)

  Criteria criteria = session.createCriteria(YourEntity.class);
  Projection idCountProjection = Projections.countDistinct(uniqueField);
  criteria.setProjection(idCountProjection);
  //setup criteria, joins etc here
  int totalResultCount = ((Long)criteria.uniqueResult()).intValue();

2) reset projection and set start and length (you want the distinct ids)

  criteria.setProjection(Projections.distinct(Projections.property(uniqueField)));
  criteria.setFirstResult(start); 
  criteria.setMaxResults(length);
  List uniqueSubList = criteria.list();

3) reset projection and get distinct results that match ids

  criteria.setProjection(null);
  criteria.setFirstResult(0); criteria.setMaxResults(Integer.MAX_VALUE);
  criteria.add(Restrictions.in(uniqueField, uniqueSubList));
  criteria.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);
  List searchResults = criteria.list();
  //and now, however you want to return your results
  Map searchResultsMap = new HashMap();
  searchResultsMap.put("searchResults", searchResults);
  searchResultsMap.put("totalResultCount", totalResultCount);