code: public void addOrderBy(String fieldName, boolean sortAscending)
      {
          if (fieldName != null)
          {
              m_orderby.add(new FieldHelper(fieldName, sortAscending));
          }
      }
docs: Adds a field for orderBy
  @param  fieldName    The field name to be used
  @param  sortAscending    true for ASCENDING, false for DESCENDING