Force secondary sort always ascending

Hi,

I've got a use case where I want to do a 2-column sort. I could use aDataSort, but the problem with that is that the sorting direction is the same for both columns (either asc or desc). I want the secondary sort to always be ascending, regardless of the primary sort direction.

Let's say I have a 2-column table -- Last Name (0), First Name (1). Both columns are sortable, but when I sort by Last Name, I also want to sort by First Name ascending.

I tried using fnSortListener and fnSort, but I had trouble with the sort direction.

First attempt: (see at this fiddle -- http://live.datatables.net/isitij/2/edit#preview)

$(document).ready(function() {
  oTable = $('#myTable').dataTable();
  oTable.fnSortListener($('#myTable th#lastName').get(0), 0, secondarySortListener);
} );

function secondarySortListener() {
  // when table is sorted by vendor, also sort by product asc
  var direction = oTable.fnSettings().aaSorting[0][1];
  table.fnSort( [ [0,direction], [1,'asc'] ] );
}

This doesn't work, as the example shows. So I wondered if the direction attribute should be its opposite, so I tried reversing the direction myself:

direction == 'asc' ? direction = 'desc' : direction = 'asc';

Still no luck.

What is wrong with that code? Why doesn't it work?

I tried to do some tests on the behavior of aaSorting and it seems to me that aaSorting doesn't update the sort direction when you do fnSort.

I don't want to track the direction with some global variable, because that could lead to sorting descending first, but it needs to sort ascending first when you first click the column header.