Returning no records when changing query setFirstResult value

Question

On 1st pass through I can get the number of results based on setFirstResult and max number of records is set to 2 for testing. As a note setFirstResult() seems to be zero-based in that I have to set 1st result to 0 to get the 1st 2 records.
I remove the query from session since I read we could not re-use the query if setting the first result. Then I always create a new query and set the 1st result to the 1st row of next page which would be 2. I have 4 records that match in the database, but never get any results back.
Any help would be really appreciated !
Here's my code:
if (_databaseSession.getQuery(HOGLConstants.NAMED_QUERY_BY_PHONE) != null){_databaseSession.removeQuery(HOGLConstants.NAMED_QUERY_BY_PHONE);
createSearchByPhoneQuery(_databaseSession, searchByPhoneDTO, requestedPage, _maxRowsPerScreen);
Vector supplements = (Vector)databaseSession.executeQuery(HOGLConstants.NAMED_QUERY_BY_PHONE,_searchByPhoneDTO.getAreaCode(),_searchByPhoneDTO.getPhoneNo());
private void createSearchByPhoneQuery(DatabaseSession databaseSession, SearchByPhoneDTO searchByPhoneDTO, int requestedPage, int maxRowsPerScreen) {
          int firstRecordRow = (requestedPage - 1) * _maxRowsPerScreen;// setFirstRecord(int) is zero-based even though API does not mentionit.
          ReadAllQuery _query = new ReadAllQuery(SuppReq.class);
          ExpressionBuilder builder = query.getExpressionBuilder();
//          Define two expressions that map to the applicant's area code and phone number
          Expression areaCodeExpression =     builder.get(HOGLConstants.PERSISTAPPLICANT_AREA_CODE).equal(_searchByPhoneDTO.getAreaCode());
          Expression phoneNoExpression = builder.get(HOGLConstants.PERSISTAPPLICANT_PHONE_NO).equal(_searchByPhoneDTO.getPhoneNo());
          _query.setSelectionCriteria(areaCodeExpression.and(phoneNoExpression));
          query.setMaxRows(HOGLConstants.SEARCHRESULTS_ROWS_PER_SCREEN);
          query.addAscendingOrdering (HOGLConstants.PERSISTSUPP_REQ_ID);
//          Specify the required arguments for the query
          query.addArgument(HOGLConstants.PERSISTAPPLICANT_AREA_CODE);
          query.addArgument(HOGLConstants.PERSISTAPPLICANT_PHONE_NO);
          query.setFirstResult(firstRecordRow);
          query.setQueryTimeout(HOGLConstants.QUERYTIMEOUT);
          databaseSession.addQuery(HOGLConstants.NAMEDQUERY_BY_PHONE, _query);
     }

Answer 1

Hello,
The max rows operation is applied independently from the firstResults opperation, and is applied first. So in setting max rows to 2, you are getting rows 1 and 2, and then by applying firstResults=2, you are skipping past the second row, hence getting 0 back. This is because Max rows is applied to the statement before execution, where as firstResult is applied to the returned resultset. You will need to use firstresults=2 and maxrows=4 to get rows 3+4.
Also, you can change the query parameters on a named query. It is not recommended though only because named queries are stored on the session, and so in a multi-threaded app can cause problems when two threads try to execute the same query with, for example, different max results set. In a multithreaded environment you might want to get the named query and clone it before changing first/max rows, but for single threaded app there shouldn't be any problems.
Best Regards,
Chris