My pretty permalink clearly shows the query_var:


Yet when I run


I get NULL returned.

Any reason why? Also when I print_r($wp_query), I can't find 'tree' anywhere.

  • well first, that isn't a pretty permalink, it's a query string argument. what is tree? is it a registered query var? – Milo Sep 27 '12 at 15:54
  • @Milo - I'm elaborating on the url. It's more like localhost/site/category/?tree=312. I added the query_arg when I displayed the link: add_query_arg('tree',$post->ID,get_permalink($post->ID)); I'm basically passing the ID in the URL and I thought I'd give it a name of 'tree'. – AlxVallejo Sep 27 '12 at 15:56
  • I guess I'm suppose to register it, huh? – AlxVallejo Sep 27 '12 at 15:58
  • yes, see my answer. – Milo Sep 27 '12 at 15:59
  • ps. not 'elaborating' but the opposite of that :) – AlxVallejo Sep 27 '12 at 16:10

You have to add any query vars that are not WordPress objects to the array of recognized query vars to be able to retrieve it from the $wp_query global:

add_filter( 'query_vars', 'wpa66452_query_vars' );
function wpa66452_query_vars( $query_vars ){
    $query_vars[] = 'tree';
    return $query_vars;
  • Would it be more efficient to run global $wp; $wp >add_query_var('tree'); ? – AlxVallejo Sep 27 '12 at 16:03
  • no difference in efficiency, but the filter is the proper way to add them – Milo Sep 27 '12 at 17:33
  • Note: I had the same issue, add_filter fixed it but I also had to declare my $page variable below get_header() – hellojebus Feb 7 '17 at 0:00

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