get_categories for custom post type with a specific custom taxonomy attached

3 comments

1. Hi @daveaspi:

   What you want to do is common but not well handled in WordPress core. There are probably ways to do it without custom SQL but I don’t think they would scale for a large number of posts. Below is a function I wrote called get_cross_referenced_terms() that will get what you want, complete with an example how to use it.

   This following code can be placed in the root of your WordPress site in a test.php file to
   see it work. You can then copy the function get_cross_referenced_terms() into your theme’s functions.php file or into a .php file of a plugin you might be working on:

   <?php 
   
     include('wp-load.php');
   
     $nike = get_term_by('slug','nike','brand'); // This here just to illustrate
   
     $terms = get_cross_referenced_terms(array(
       'post_type'        => 'product',
       'related_taxonomy' => 'brand',
       'term_id'          => $nike->term_id,
     ));
     foreach($terms as $term) {
       echo "<p>{$term->name}</p>";
     }
   
   function get_cross_referenced_terms($args) {
     global $wpdb;
     $args = wp_parse_args($args,array(
       'post_type'        => 'post',
       'taxonomy'         => 'category',
       'related_taxonomy' => 'post_tag',
       'term_id'          => 0,
     ));
     extract($args);
     $sql = <<<SQL
   SELECT DISTINCT
     {$wpdb->terms}.*,
     COUNT(*) AS post_count
   FROM
     {$wpdb->terms}
     INNER JOIN {$wpdb->term_taxonomy} ON {$wpdb->terms}.term_id={$wpdb->term_taxonomy}.term_id
     INNER JOIN {$wpdb->term_relationships} ON {$wpdb->term_taxonomy}.term_taxonomy_id={$wpdb->term_relationships}.term_taxonomy_id
     INNER JOIN {$wpdb->posts} ON {$wpdb->term_relationships}.object_id={$wpdb->posts}.ID
     INNER JOIN {$wpdb->term_relationships} related_relationship ON {$wpdb->posts}.ID=related_relationship.object_id
     INNER JOIN {$wpdb->term_taxonomy} related_term_taxonomy ON related_relationship.term_taxonomy_id=related_term_taxonomy.term_taxonomy_id
     INNER JOIN {$wpdb->terms} related_terms ON related_term_taxonomy.term_id=related_terms.term_id
   WHERE 1=1
     AND (related_term_taxonomy.taxonomy<>{$wpdb->term_taxonomy}.taxonomy OR related_terms.term_id<>{$wpdb->terms}.term_id)
     AND {$wpdb->posts}.post_type='%s'
     AND {$wpdb->term_taxonomy}.taxonomy='%s'
     AND related_term_taxonomy.taxonomy='%s'
     AND related_terms.term_id=%d
   GROUP BY
     {$wpdb->terms}.term_id
   SQL;
     $sql = $wpdb->prepare($sql,$post_type,$taxonomy,$related_taxonomy,$term_id);
     $terms = $wpdb->get_results($sql);
     return $terms;
   }
   

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2. If you want to list all the available categories for a custom post type, this snippet might help you.

   Just use the standard get_categories() function and pass the $args relating to the taxonomy you registered for your CPT. So, if you defined your taxonomy like this:

   register_taxonomy( 'the_taxonomy_named_in_your_CPT' );
   

   Then you’d show the taxonomy to front end users via:

   $args = array( 
       'taxonomy'     => 'the_taxonomy_named_in_your_CPT',
       'orderby'      => 'name',
       'show_count'   => 1,
       'pad_counts'   => 1, 
       'hierarchical' => 1,
       'echo'         => 0
   );
   
   $allthecats = get_categories( $args );
   echo ( '<pre>' );
   print_r( $allthecats );
   echo ( '</pre>' );
   

   You will see an object which will help you on your way.

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3. You can either code a custom sql query or you can query your post type for that “brand” and collect the categories and then display them, something like:

   //get all your post of that type fo that spesific brand
   $my_query = new WP_Query();
   $my_query->query(array(
       'post_type' => 'products',
       'posts_per_page' => -1,
       'tax_query' => array(
           array(
               'taxonomy' => 'brand',
               'field' => 'slug',
               'terms' => $wp_query->query_vars['brand']
           )
       )
       ));
   $my_cats = array(); 
   if ($my_query->have_posts()){
   //loop over all post and collect the categories in to an array
       while ($my_query->have_posts()){
           $my_query->the_post();
           foreach((get_the_category($post->ID)) as $category) {
               if (!in_array($category->cat_ID ,$my_cats)){
                   $my_cats[] = $category->cat_ID;
               }
           } 
       }
   }
   

   and here you have the list of all categories ID in an array $my_cats.
   which you can get all the info you need from

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