Add post classes for custom taxonomies to custom post type?

Question

I was surprised to learn that custom taxonomies aren't added as body or post classes like categories and tags are.

I'm sure this will be added in a future version of WordPress, but in the meantime I need to add a custom taxonomy to the post class so that I can style post in a certain category in that taxonomy differently.

It'd be most elegant to filter the post class and add the taxonomies to it. I found a snippet to pull off a similar trick with the body class, but I haven't been successful in adapting it:

function wpprogrammer_post_name_in_body_class( $classes ){
 if( is_singular() )
 {
  global $post;
  array_push( $classes, "{$post->post_type}-{$post->post_name}" );
 }
 return $classes;
}

add_filter( 'body_class', 'wpprogrammer_post_name_in_body_class' );

A bit more crudely, I thought about using the_terms function to create my own classes for the custom posts, something like this:

<div class="<?php the_terms( $post->ID, 'taxonomy', '', ' ', '' ); ?>"></div>

But then I'd have to filter out the HTML that the_term generates.

Am I missing anything obvious here, is there a simpler way to solve this issue?

Answer 1

I found a snippet of code courtesy of mfields that solved this problem for me, here's what I ended up using:

<?php   // Add custom taxonomies to the post class

    add_filter( 'post_class', 'custom_taxonomy_post_class', 10, 3 );

    if( !function_exists( 'custom_taxonomy_post_class' ) ) {

        function custom_taxonomy_post_class( $classes, $class, $ID ) {

            $taxonomy = 'listing-category';

            $terms = get_the_terms( (int) $ID, $taxonomy );

            if( !empty( $terms ) ) {

                foreach( (array) $terms as $order => $term ) {

                    if( !in_array( $term->slug, $classes ) ) {

                        $classes[] = $term->slug;

                    }

                }

            }

            return $classes;

        }

    }  ?>

Answer 2

Update: As of WordPress 4.2-alpha-31271 (23 January 2015), CSS classes for custom taxonomy terms are now automatically added by WordPress core when using get_post_class().

The following code snippet is no longer necessary.

---

Here's a good utility function that will add all registered, public taxonomy terms to the post_class() for use as CSS hooks in themes:

/**
* Add Custom Taxonomy Terms To The Post Class
*/

add_filter( 'post_class', 'wpse_2266_custom_taxonomy_post_class', 10, 3 );

if ( ! function_exists('wpse_2266_custom_taxonomy_post_class') ) {
    function wpse_2266_custom_taxonomy_post_class($classes, $class, $ID) {

        $taxonomies_args = array(
            'public' => true,
            '_builtin' => false,
        );

        $taxonomies = get_taxonomies( $taxonomies_args, 'names', 'and' );

        $terms = get_the_terms( (int) $ID, (array) $taxonomies );

        if ( ! empty( $terms ) ) {
            foreach ( (array) $terms as $order => $term ) {
                if ( ! in_array( $term->slug, $classes ) ) {
                    $classes[] = $term->slug;
                }
            }
        }

        $classes[] = 'clearfix';

        return $classes;
    }
}

Inspiration and credit from Jan Fabry's previous answer.

Put the above code in your theme's functions.php file. Then, whenever the post_class() is used in a template:

<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>

It will output any public custom taxonomy term(s) attached to the post, in addition to all of the default post classes. For example:

<article id="post-247" class="post-247 post-type ... status-publish hentry clearfix">

It handily works with Custom Post Types and Taxonomies.

Answer 3

I have an improvement on @rjb's answer (I don't have enough reputation to comment, sorry). I was getting an "array to strings conversion" error with debug mode turned on, so I did a foreach loop of the returned taxonomies and now there's no error.

Hope this helps someone!

add_filter( 'post_class', 'custom_taxonomy_post_class', 10, 3 );

function custom_taxonomy_post_class($classes, $class, $ID) {

    $taxonomies_args = array(
        'public' => true,
        '_builtin' => false,
    );

    $taxonomies = get_taxonomies( $taxonomies_args, 'names', 'and' );

    foreach ($taxonomies as $taxonomy) {

    $terms = get_the_terms( (int) $ID, $taxonomy );

    if ( ! empty( $terms ) ) {
        foreach ( (array) $terms as $order => $term ) {
            if ( ! in_array( $term->slug, $classes ) ) {
                $classes[] = $term->slug;
            }
        }
    }


}

    $classes[] = 'clearfix';

    return $classes;
}

Answer 4

Instead of the_terms, you could use get_the_terms, which will return the taxonomy term objects. The Codex has documentation for the tag-only version, get_the_tags.

That would give you something like this:

function wpprogrammer_custom_taxonomy_in_body_class( $classes ){
  if( is_singular() )
  {
    $custom_terms = get_the_terms(0, 'my_custom_taxonomy');
    if ($custom_terms) {
      foreach ($custom_terms as $custom_term) {
        $classes[] = 'custom_tag_' . $custom_term->slug;
      }
    }
  }
  return $classes;
}

add_filter( 'body_class', 'wpprogrammer_custom_taxonomy_in_body_class' );

Answer 5

I did some coding and I add support of post class, to my plugin called: Custom post types and taxonomies manager

In new taxonomy form is option called Post class. Which allows to add category|tag-{slug} and {slug}-{tax_value_slug} to the post class.

Download here https://github.com/Pravdomil/wp-custom-post-types-man/archive/master.zip