I search around but cannot find anything that can provide this. Here it goes:-

I have a views that would display a list of available sports to register on a child node (of content type named Child). So when user viewing the child node, together with the information about the child such as age, class, dob etc, a list of available sports for them to register would be displayed below. This can easily be achieved with views_attach. I created a views with all field that I want, add another Node Content display and set it to display on Child content type.

Now I want to add another field, using the standard Global custom field that would be a link to a form that they need to fill in to register. For the path to this form, I need 2 information - The child node id and the sports node id. Something like:-

child/[nid_of_child]/sports/register/[nid_of_sports].

The problem is the [nid_of_child], it's not available in the list of fields that I can add to the views. Looking in this module code, especially in hook_nodeapi, I know that the views that being displayed is attached to the current node, so somehow the node properties already available to the views (around line 119 of views_attach.module):-

        if ($view->access($info['display'])) {
          $view->current_node = $node;
          $result = $view->execute_display($info['display']);
          if (!empty($result)) {
          .... //

So, taking a look at how views_customfield work (actually how to provide additional field to the views2), I managed to get this working. Basically it just defining the hook_views_data and hook_views_handler to define the new field and return the value of $this->view->current_node->nid in the handler.

Some blind copy n paste from views_customfield module:-

function views_attach_views_data() {
  $data['attachfield']['table']['group'] = t('Attachfield');
  $data['attachfield']['table']['join'] = array(
    '#global' => array(),
  );

  $data['attachfield']['attached_nid'] = array(
    'title' => t('Attached Node nid'),
    'help' => t('Nid of attached node'),
    'field' => array(
      'handler' => 'views_attach_handler_field_nid',
      'click sortable' => FALSE,
      'notafield' => TRUE,
    ),
  );

  return $data;
}

class views_attach_handler_field_nid extends views_handler_field {
  var $rownumber;

  function init(&$view, $options) {
    parent::init($view, $options);

    $this->rownumbers = 0;
  }

  function query() {
    // Override parent::query() and don't alter query.
    $this->field_alias = 'views_attach_nid_'. $this->position;
  }

  function render($values) {
    return $this->view->current_node->nid;
  }
}

If this is something useful to views_attach, I'm willing to create proper patch for this or if someone could lead me to better solution without me hacking the code.