Custom post types and taxonomies

Posts and pages are just two built-in content types. Books, products, job openings, reviews and events are better kept in types of their own: each gets its own dashboard section, addresses and templates.

Registering a type

// books.php (a plugin)
 
add_action('init', function () {
    register_post_type('book', [
        'labels' => [
            'name' => 'Books',
            'singular_name' => 'Book',
            'add_new_item' => 'Add a book',
            'edit_item' => 'Edit book',
        ],
        'public' => true,
        'has_archive' => true,
        'menu_icon' => 'dashicons-book',
        'supports' => ['title', 'editor', 'thumbnail', 'excerpt'],
        'rewrite' => ['slug' => 'books'],
        'show_in_rest' => true,
    ]);
});

A "Books" section appears in the dashboard, the list of books opens at /books/, and a single book at /books/title/.

The main settings

Setting	Meaning
`public`	The type is visible on the site and in the dashboard
`has_archive`	There is a list page
`supports`	Which fields the editor has
`rewrite`	The part of the address
`menu_icon`	The icon in the dashboard menu
`show_in_rest`	Available in the REST API and the block editor
`hierarchical`	Posts can nest inside each other, like pages

A custom taxonomy

A taxonomy is a way to group posts. Categories and tags are built-in taxonomies; for books let us add genres:

add_action('init', function () {
    register_taxonomy('genre', 'book', [
        'labels' => [
            'name' => 'Genres',
            'singular_name' => 'Genre',
        ],
        'public' => true,
        'hierarchical' => true,
        'rewrite' => ['slug' => 'genre'],
        'show_in_rest' => true,
    ]);
});

hierarchical: true makes the taxonomy resemble categories — with nesting; false makes it resemble tags.

Templates

By the template hierarchy the new type gets files of its own:

File	Used for
`single-book.php`	The page of one book
`archive-book.php`	The list of books
`taxonomy-genre.php`	Books of one genre

<?php
// single-book.php
 
get_header();
 
while (have_posts()) :
    the_post();
    ?>
    <article class="book">
        <h1><?php the_title(); ?></h1>
        <?php the_post_thumbnail('large'); ?>
        <p class="genres"><?php the_terms(get_the_ID(), 'genre', 'Genre: ', ', '); ?></p>
        <?php the_content(); ?>
    </article>
    <?php
endwhile;
 
get_footer();

Theme or plugin

Post types are registered in a plugin. If they are declared in a theme, the "Books" section disappears from the dashboard after a change of design, although the posts themselves stay in the database.

Common mistake

Right after a new type is registered, its pages return a 404 error: WordPress has not updated its address rules yet. Open "Settings → Permalinks" and press "Save" — the rules are rebuilt. A plugin does this once on activation:

register_activation_hook(__FILE__, function () {
    books_register_types();
    flush_rewrite_rules();
});

Never call flush_rewrite_rules() on every load of the site: it is a slow operation.

Thanks for reading!