JPA: what is the proper pattern for iterating over large result sets?

Question

Let\'s say I have a table with millions of rows. Using JPA, what\'s the proper way to iterate over a query against that table, such that I don\'t have all an in-memo

Answer 1

If you use EclipseLink I' using this method to get result as Iterable

private static  Iterable getResult(TypedQuery query)
{
  //eclipseLink
  if(query instanceof JpaQuery) {
    JpaQuery jQuery = (JpaQuery) query;
    jQuery.setHint(QueryHints.RESULT_SET_TYPE, ResultSetType.ForwardOnly)
       .setHint(QueryHints.SCROLLABLE_CURSOR, true);

    final Cursor cursor = jQuery.getResultCursor();
    return new Iterable()
    {     
      @SuppressWarnings("unchecked")
      @Override
      public Iterator iterator()
      {
        return cursor;
      }
    }; 
   }
  return query.getResultList();  
}  

close Method

static void closeCursor(Iterable list)
{
  if (list.iterator() instanceof Cursor)
    {
      ((Cursor) list.iterator()).close();
    }
}