Custom Taxonomy

Register Taxonomy

Suppose you created a Custom Post Type(CPT) named Portfolio and need a taxonomy for it named Project Type, Then code is:

//hook into the init action and call create_book_taxonomies when it fires
add_action( 'init', 'create_subjects_hierarchical_taxonomy', 0 );
 
//create a custom taxonomy name it subjects for your posts
function create_subjects_hierarchical_taxonomy() {
 
// Add new taxonomy, make it hierarchical like categories
//first do the translations part for GUI
 
  $labels = array(
    'name' => _x( 'Project Type', 'taxonomy general name' ),
    'singular_name' => _x( 'Project Type', 'taxonomy singular name' ),
    'search_items' =>  __( 'Search Category' ),
    'all_items' => __( 'All Categories' ),
    'parent_item' => __( 'Parent Categories' ),
    'parent_item_colon' => __( 'Parent Category:' ),
    'edit_item' => __( 'Edit Category' ), 
    'update_item' => __( 'Update Category' ),
    'add_new_item' => __( 'Add New Category' ),
    'new_item_name' => __( 'New Project Type' ),
  );    
 
// Now register the taxonomy
  register_taxonomy('project-type',array('portfolio'), array(
    'hierarchical' => true,
    'labels' => $labels,
    'show_ui' => true,
    'show_in_rest' => true,
    'show_admin_column' => true,
    'query_var' => true,
    'rewrite' => array( 'slug' => 'subject' ),
  ));
 
}

Get custom template part if custom taxonomy

In your archive.php file, you will find ‘get_template_part( ‘template-parts/content’, get_post_format();‘. Replace it by following code:

if ( has_term( '', 'custom_taxonomy' ) ) {
	get_template_part( 'template-parts/content', 'portfolio' );
} else {
	get_template_part( 'template-parts/content', get_post_format() );
}

Custom CPT Category / Taxonomy Listing

You can use it in any page template or archive page.

   $args = array(
	   'taxonomy' => 'project-type',
	   'order'   => 'ASC'
   );

   $categories = get_categories($args);
   echo '<ul>';

   foreach ($categories as $category) {
	 $url = get_term_link($category);?>
	  <li><a href="<?php echo $url;?>"><?php echo $category->name; ?></a></li>
	 <?php
   }
   echo '</ul>';