Drupal 6: Filtering a view’s exposed filter options to show relevant nodes

Recently I was working on a project that had a view with an exposed filter for country (via location module) and the dropdown list by default showed the entire country list, which was very large. I decided to write a code snippet that would reduce the select options to show only the countries that have been assigned to the nodes.

In my sandbox I create a simple node type for “person” that used the location module to capture the user’s country. I then created a view to show the people’s names and countries, and added an exposed filter for country.

Clicking on the exposed filter showed all of the available countries, which was a very large list.

I added the following code to my module to alter the exposed filter form and reduce the country list. (Please note, an alternative approach would be to modify the views object, I wanted to show how this could be accomplished in hook_form_alter())

<?php
/**
 * Implements hook_form_alter()
 */
function MYMODULE_form_alter(&$form, $form_state, $form_id) {

  // define variables
  $view_name = 'people_places';
  $filer_name = 'country';

  // modify country drop down
  if ($form_id == 'views_exposed_form' && is_object($form_state['view']) && $form_state['view']->name==$view_name && is_array($form[$filer_name])) {

    // define SQL to fetch nodes that have countries
    $sql = "
      select distinct
        l.country
      from
        {node} n
      join
        {location_instance} li on li.nid = n.nid and li.vid = n.vid
      join
        {location} l on l.lid = li.lid
      where
       n.status = 1 and n.type = 'person'
    ";

    // fetch results
    $resource = db_query($sql, $tid);
    $countries = array();
    while($row = db_fetch_object($resource)) {
      $countries[] = $row->country;
    }

    // filter country list
    foreach($form[$filer_name]['#options'] as $key => $value) {

      // allow "All"
      if ($key == 'All') {
        continue;
      }

      elseif (!in_array($key, $countries)) {
        unset($form[$filer_name]['#options'][$key]);
      }

    }

  }
}
?>

Now the view only shows countries that match the resulting nodes.