Fortunately, Drupal provides you with taxonomy_node_get_terms_by_vocabulary(). In Drupal 6, this takes the $node object and a vocabulary ID. Then you just have to cycle through the terms it returns and see if your term is in there.

In my case, I have some pages that need to be publicly accessible, but must not be in Google or other indexes. So I let those get tagged with a special taxonomy term (“custom” in my case, but it could be “noindex” or anything). All you need to know is the vocabulary ID and the term ID for the term you’re testing for and you can apply the meta noindex to any node. Sometimes node_load() carries a high cost, but since we’re only testing this on nodes and we’re testing for the node in question, that data should be cached and should not result in another database query.

function MYTHEME_preprocess_page(&$vars, $hook) {

// if this is a node and not being edited and it is tagged with term 41, then add a "noindex" tag
   if (arg(0) == 'node' && is_numeric(arg(1)) && is_null(arg(2))) {
	    $node = node_load(arg(1));
	    $terms = taxonomy_node_get_terms_by_vocabulary($node, 2);

		foreach($terms as $term) {
		  if ($term->tid == '41') {
			$vars['head'] = drupal_set_html_head('<meta name="robots" content="noindex" />');
		    break;
		  }
		}
	}
}

In order to get the meta tag to show, you’ll need to clear your caches.

• 1. United States
  • 3. California
  • 4. Vermont
• 2. Canada
  • 5. Alberta

I want it so that if I tag something as California (term 3), it also gets tagged as United States (term 1). The Hierarchical Select module does this, and much more, but it has conflicts with other Drupal modules I want to use, so I just gave up on it.

Finally, I realized that I could simply turn it around and solve this on the data retrieval end, rather than the data storage end. In Drupal, if you enter a standard Drupal path like /taxonomy/term/1, that shows only nodes tagged as United States, but /taxonomy/term/1/all shows all nodes tagged United States and all nodes tagged with child terms.

I’m trying to build a drill-down directory of professional ski instructors (emphasis on trying — it’s still pretty rudimentary now and doesn’t yet have any instructors really). I realized that I could use the Advanced Taxonomy Blocks module to navigate for the drill down and was looking to create an add-on module or a patch for the module so that I could have it add the “all” to the end of the URL. Then I saw this in the settings:

All you have to do is add the /all to the end of the path. It’s built right in to the module settings (go to /admin/settings/taxonomyblocks and click Configure).

So much thanks to Aaron Hawkins, an awesome drupal developer, for this simple way around my problem.