var table = $('#products_table').DataTable();
<% @pre_purchases.each do |pre_purchase| %>
	var newRow = $('<%= j render (pre_purchase) %>');
	x = $('#products_table').dataTable();
	newRow.find('td:eq(0)').html(newRow.find('td:eq(0)').html().replace('#', x.fnGetData().length + 1));
	table.row.add($(newRow)).draw();
<% end %>
$('#dialog').modal('toggle');
calculateTotals();