@Override
 public int hashCode() {
   int result = super.hashCode();
   result = 31 * result + joinField.hashCode();
   result = 31 * result + toQuery.hashCode();
   result = 31 * result + fromQuery.hashCode();
   result = 31 * result + indexReader.hashCode();
   return result;
 }
 /** @see LuceneIndexReader#hashCode() */
 public int hashCode() {
   return indexReader.hashCode();
 }