Custom Taxonomy specific to a Custom Post type

Question

I want to create a custom taxonomy which behaves similar to the post type as a category behaves to a the default posts (on the grounds of /%category%/%postname%/ permalink structure) so that the posts in the custom post types are displayed as www.example.com/custom-post-type/custom-taxonomy-name/post-name Also I want the category meta box to appear only when we add new default post and not when we add a new post in the custom post type and the custom taxonomy box to appear only when we add a new post in the custom post type and not when we add new a default post.

Answer 1

First of all if you want to show taxonomy metabox only to custom post type then register the taxonomy to only that custom post type by passing the custom post type name as argument in register_taxonomy. By doing this the taxonomy metabox appears only to custom post type. If your don't want to show category metabox to custom post type then remove the term category as argument while registering custom post type and instead include the taxonomy slug name like this 'taxonomies' => array( 'post_tag','your_taxonomy_name'). here is the code how i achieved that. I have registered a custom taxonomy with slug themes_categories under under custom post type themes

function themes_taxonomy() {  
    register_taxonomy(  
        'themes_categories',  //The name of the taxonomy. Name should be in slug form (must not contain capital letters or spaces). 
        'themes',        //post type name
        array(  
            'hierarchical' => true,  
            'label' => 'Themes store',  //Display name
            'query_var' => true,
            'rewrite' => array(
                'slug' => 'themes', // This controls the base slug that will display before each term
                'with_front' => false // Don't display the category base before 
            )
        )  
    );  
}  
add_action( 'init', 'themes_taxonomy');

Then to change the permalink i have created following function

function filter_post_type_link($link, $post)
{
    if ($post->post_type != 'themes')
        return $link;

    if ($cats = get_the_terms($post->ID, 'themes_categories'))
        $link = str_replace('%themes_categories%', array_pop($cats)->slug, $link);
    return $link;
}
add_filter('post_type_link', 'filter_post_type_link', 10, 2);

Then i registered a custom post type with slug themes as below

//Registering Custom Post Type Themes
add_action( 'init', 'register_themepost', 20 );
function register_themepost() {
    $labels = array(
        'name' => _x( 'Themes', 'my_custom_post','custom' ),
        'singular_name' => _x( 'Theme', 'my_custom_post', 'custom' ),
        'add_new' => _x( 'Add New', 'my_custom_post', 'custom' ),
        'add_new_item' => _x( 'Add New ThemePost', 'my_custom_post', 'custom' ),
        'edit_item' => _x( 'Edit ThemePost', 'my_custom_post', 'custom' ),
        'new_item' => _x( 'New ThemePost', 'my_custom_post', 'custom' ),
        'view_item' => _x( 'View ThemePost', 'my_custom_post', 'custom' ),
        'search_items' => _x( 'Search ThemePosts', 'my_custom_post', 'custom' ),
        'not_found' => _x( 'No ThemePosts found', 'my_custom_post', 'custom' ),
        'not_found_in_trash' => _x( 'No ThemePosts found in Trash', 'my_custom_post', 'custom' ),
        'parent_item_colon' => _x( 'Parent ThemePost:', 'my_custom_post', 'custom' ),
        'menu_name' => _x( 'Themes Posts', 'my_custom_post', 'custom' ),
    );

    $args = array(
        'labels' => $labels,
        'hierarchical' => false,
        'description' => 'Custom Theme Posts',
        'supports' => array( 'title', 'editor', 'excerpt', 'author', 'thumbnail', 'comments', 'revisions', 'post-formats', 'custom-fields' ),
        'taxonomies' => array( 'post_tag','themes_categories'),
        'show_ui' => true,
        'show_in_menu' => true,
        'menu_position' => 5,
        'menu_icon' => get_stylesheet_directory_uri() . '/functions/panel/images/catchinternet-small.png',
        'show_in_nav_menus' => true,
        'publicly_queryable' => true,
        'exclude_from_search' => false,
        'query_var' => true,
        'can_export' => true,
        'rewrite' => array('slug' => 'themes/%themes_categories%','with_front' => FALSE),
        'public' => true,
        'has_archive' => 'themes',
        'capability_type' => 'post'
    );  
    register_post_type( 'themes', $args );//max 20 charachter cannot contain capital letters and spaces
}  

There are few things you have to remember while registering custom post. change the has_archive parameter to custom post type slug name and another is change the rewrite slug name as 'slug' => 'custom_post_type_slug/%taxonomy_slug%

Now when you add a new post type in the write post type page... you will see the permalink as http://www.example.com/wordpress/themes/%themes_categories%/post-name/. If the custom taxonomy for this post is not selected then the permalink will remain http://www.example.com/wordpress/themes/%themes_categories%/post-name/ which will then show a bad request. To correct this we create a default term in the custom taxonomy. (same as uncategorized in categories) Add this to functions.php

function default_taxonomy_term( $post_id, $post ) {
    if ( 'publish' === $post->post_status ) {
        $defaults = array(
            'themes_categories' => array( 'other'),   //

            );
        $taxonomies = get_object_taxonomies( $post->post_type );
        foreach ( (array) $taxonomies as $taxonomy ) {
            $terms = wp_get_post_terms( $post_id, $taxonomy );
            if ( empty( $terms ) && array_key_exists( $taxonomy, $defaults ) ) {
                wp_set_object_terms( $post_id, $defaults[$taxonomy], $taxonomy );
            }
        }
    }
}
add_action( 'save_post', 'default_taxonomy_term', 100, 2 );

Now when the custom taxonomy is left blank the permlaink becomes http://www.example.com/wordpress/themes/other/post-name/ automatically.

At last don't forget to flush the rewrite by clicking on save changes in permalink setting in admin section otherwise you will be redirected to 404 error. Hope this helps you.