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I'm facing an issue with the is_tax() function.

I'm a class method that fetches a specific custom post types. These custom post types have taxonomy related custom fields (among other custom fields).

If in these custom fields I find, for instance, a value for the category term "discografia", I want my method to return this custom post type if I'm currently seeing the archive page /category/discografia.

This is an excerpt of my code:

// The Query
/** @var $query WP_Query */
$query = new WP_Query($query_args);

$results = false;
// The Loop
if ($query->have_posts()) {
    if (!is_home() && !is_front_page()) {
        $posts = $query->get_posts();
        foreach ($posts as $post) {
            $add = false;
            //ServiceBoxes::getBox returns the $post object as Array_A
            //and adds a new key "meta" with the custom fields I want to use
            $box = ServiceBoxes::getBox($post->ID);
            if (is_archive()) {
                if (isset($box['meta'][self::$prefix]['taxonomies'])) {
                    foreach ($box['meta'][self::$prefix]['taxonomies'] as $tax => $terms) {
                        if ($terms) {
                            if (is_tax($tax, $terms)) {
                                $add = true;
            if ($add) $results[] = $box;

    } else {
        $results = $query->get_posts();

    return $results;
return false;

Some clarification about what happens here: 1. $box['meta'][self::$prefix]['taxonomies'] actually returns an array with "category" as key and an array of terms (including "discografia") 2. The url /category/discografia/ actually returns a series of posts 3. is_tax($tax, $terms) returns false 4. Also is_tax('category', 'discografia') returns false

I suspect that the instance of WP_Query inside my method is overriding the global query, but I don't see why: it's a new instance, there is no reason for is_tax() to get confused.

However, with some step-by-step debugging here's what happens in is_tax when called as is_tax('category', array('discografia')):

  • $wp_query->is_tax( $taxonomy, $term ) is called by is_tax()
  • in $wp_query->is_tax(), if ( !$this->is_tax ) returns false

I've been able to reach this point: after that, I don't know what else I can do to understand why the is_tax property is not set as expected.

With the debugger on and some variables in the watch list, here is what I can see when calling "/category/discografia/" (an archive page that, I repeat, returns posts): http://www.evernote.com/shard/s6/sh/88f05447-edff-40c7-9670-902f0a92bc62/b50a28d39c9e55c7d404f912175975a4

share|improve this question
Can you show an example of the structure of $box['meta'][self::$prefix]['taxonomies'] ? It sounds like the problem might be in the foreach loop on this array, where $tax=>$terms are not assigned the values you expect. You should try debugging these values. – birgire Jul 2 '13 at 11:39
I did it: $tax = "category", $terms = array('discografia') It's not a foreach issue: as I wrote, the is_tax() function called with hardcoded values returns false as well. – Andrea Sciamanna Jul 2 '13 at 11:50
does is_category( array( 'discografia' ) ) work on the category page /category/discografia/ ? – birgire Jul 2 '13 at 11:55
Yes, it does return true (see my last update). – Andrea Sciamanna Jul 2 '13 at 12:02
up vote 1 down vote accepted

If you take a look at this part of the WP_Query class:

            switch ( $tax_query['taxonomy'] ) {
                case 'category':
                    $this->is_category = true;
                case 'post_tag':
                    $this->is_tag = true;
                    $this->is_tax = true;

then it looks like on category archive pages where is_category gives true then is_tax is false.

So it looks like you will have to use a mix of is_category and is_tax ;-)


Take a look at this ticket:

is_tax() returns false when is_category() or is_tag() returns true


It's status is currently closed with wontfix!

share|improve this answer
Thank you! This made things clear... well, almost: I don't quite understand why they did that, as gategories and tags are still taxonomies, but anyway, using the same switch-case I've managed to make my code work. – Andrea Sciamanna Jul 2 '13 at 12:49
yes it's strange, but it looks like they have decided to live with it to keep the compatability unbroken ;-) – birgire Jul 2 '13 at 12:59

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