This is the confirm sale code :

    def action_button_confirm(self, cr, uid, ids, context=None):
    assert len(ids) == 1, 'This option should only be used for a single id at a time.'
    wf_service = netsvc.LocalService('workflow')
    wf_service.trg_validate(uid, 'sale.order', ids[0], 'order_confirm', cr)

    # redisplay the record as a sales order
    view_ref = self.pool.get('ir.model.data').get_object_reference(cr, uid, 'sale', 'view_order_form')
    view_id = view_ref and view_ref[1] or False,
    return {
        'type': 'ir.actions.act_window',
        'name': _('Sales Order'),
        'res_model': 'sale.order',
        'res_id': ids[0],
        'view_type': 'form',
        'view_mode': 'form',
        'view_id': view_id,
        'target': 'current',
        'nodestroy': True,
    }

It write "assert len(ids) == 1, 'This option should only be used for a single id at a time.'"

So how can I change it , then I can do it with many ids at a time. I try to delete this sentence, but it doesn't work. Should I change the "return" and "ids[0]"as well ?