Output slugs to use as class names for every taxonomy a post is attached to

Question

I'm trying to output slugs as class names for all of the taxonomies that a post is attached to, so I can filter those posts using MixItUp3 with the Multifier Extension on a custom directory page.

I have a custom loop setup that only pulls through directory posts that have been tagged 'current' (this allows old listings to remain in the system but not be displayed).

<?php 

$args = array(
    'post_type' => 'directory',
    'tax_query' => array(
    'relation' => 'AND',
        array(
            'taxonomy' => 'directory_cat',
            'operator' => 'EXISTS'
        ),
        array(
            'taxonomy' => 'directory_tag',
            'field' => 'slug',
            'terms' => 'current'
        )
    )
);

$query = new WP_Query( $args ); if ( $query->have_posts() ) : while ( $query->have_posts() ) : $query->the_post();

?>

<div class="column mix<?php if ($class_names) { echo ' ' . $class_names;} ?>">
    <a href="<?php the_permalink(); ?>">
        ...
    </a>
</div>

I'm trying to output the slugs into the div class as shown above ($class_names), but I can't find the right way to do it. The following code was taken from the MixItUp documentation and I've tried to edit it to my needs but as a php beginner I just keep faltering.

$taxonomies = get_terms();
$slugs = wp_list_pluck($taxonomies, 'slug');
$class_names = join(' ', $slugs);

It outputs and formats correctly but it lists every taxonomy in the system, rather than the ones attached to each post in the loop.

Answer 1

I'd recommend using get_the_terms instead of get_terms. It specifically pulls out the terms that are attached to a given post. If you use it within the loop, it'll only give you the terms that are attached to that post.

It'd look something like this:

$query = new WP_Query( $args ); if ( $query->have_posts() ) : while ( $query->have_posts() ) : $query->the_post();

$slugs = array();    
$directory_terms = get_the_terms( $post->ID, 'directory_tag');

foreach ( $directory_terms as $term ) {
    $slugs[] = $term->slug;
}

$class_names = join( ' ', $slugs ); 

?> 

<div class="' . <?php if ( isset( $class_names) ) { echo ' ' . $class_names;} ?> . '"> 

You could obviously refine your search further if you only need specific terms from that taxonomy. get_the_terms returns a list of WP_Term objects that you can narrow down in any way you see fit.

EDIT: Updated code to show how to implement in a div.

EDIT: Added missing semi-colon.