Custom post types

One of the more common use cases for developing a custom plugin is to take advantage of the WordPress Post API to create custom post types.

Building an online bookstore

Let’s say you’re building an online bookstore, and you want to store data about the books that are for sale.

The WordPress core Post API allows you to register custom post types. These custom post types extend the core post data type, which is stored in the posts table in the WordPress database.

An example of a custom post type is the page data type, which is registered by WordPress core.

Using the WordPress POST API, you could create a custom post type to store information about books.

When you register a custom post type correctly, WordPress will automatically create a new admin menu item for your custom post type, and admin pages to manage the data.

To register a custom post type, you use the WordPress register_post_type function.

As you can see from the function reference page in the WordPress developer documentation, this function takes two parameters: the name of the custom post type, and an array of arguments that define the custom post type.

Parameters are the names of the variables that you define in the function definition. In this case, the parameters are the name, as a string variable, and an array of arguments.

When you use the function, you pass in the values for these parameters. These values are called arguments.

Here’s an example of creating the arguments array, and calling the register_post_type, passing in the relevant arguments, to create the custom post type for books.

$args = array(
    'labels' => array(
            'name'          => 'Books',
            'singular_name' => 'Book',
            'menu_name'     => 'Books',
            'add_new'       => 'Add New Book',
            'add_new_item'  => 'Add New Book',
            'new_item'      => 'New Book',
            'edit_item'     => 'Edit Book',
            'view_item'     => 'View Book',
            'all_items'     => 'All Books',
    ),
    'public' => true,
    'has_archive' => true,
    'show_in_rest' => true,
    'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt' ),
);

register_post_type( 'book', $args );

Let’s look at how you could implement this code in a plugin.

Implementing the book custom post type

To start create a new plugin in the same way that you learned in the What is a plugin lesson.

Add a directory in the wp-content/plugins directory called bookstore.

Then create a new PHP file called bookstore.php inside that directory.

Inside the file, add the opening PHP tag, and the plugin header to the top of the file, as well as the ABSPATH check to prevent direct access to the file.

<?php
/**
 * Plugin Name: Bookstore
 * Description: A plugin to manage books
 * Version: 1.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit; // Exit if accessed directly
}

Next, create a new function called bookstore_register_book_post_type that will register the custom post type. Create the arguments array, and then call the register_post_type function, passing in the relevant arguments to create the custom post type for books.

function bookstore_register_book_post_type() {
     $args = array(
        'labels' => array(
            'name'          => 'Books',
            'singular_name' => 'Book',
            'menu_name'     => 'Books',
            'add_new'       => 'Add New Book',
            'add_new_item'  => 'Add New Book',
            'new_item'      => 'New Book',
            'edit_item'     => 'Edit Book',
            'view_item'     => 'View Book',
            'all_items'     => 'All Books',
        ),
        'public' => true,
        'has_archive' => true,
        'show_in_rest' => true,
        'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt' ),
    );

    register_post_type( 'book', $args );
}

Notice the use of the bookstore_ prefix in the function name.

This is an example of prefixing function names to avoid conflicts with other plugins or themes.

You can read more about this, and other methods to prevent function conflicts in the Plugin best practices page in the Plugin developer handbook.

The last step is to call the bookstore_register_book_post_type function. You need to hook into the init action to do this.

If you skipped the module on WordPress hooks, hooks that they are a way to run code at specific points in the WordPress request lifecycle.

add_action( 'init', 'bookstore_register_book_post_type' );

Your final code should look like this:

<?php
/**
 * Plugin Name: Bookstore
 * Description: A plugin to manage books
 * Version: 1.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit; // Exit if accessed directly
}

add_action( 'init', 'bookstore_register_book_post_type' );
function bookstore_register_book_post_type() {
    $args = array(
        'labels' => array(
            'name'          => 'Books',
            'singular_name' => 'Book',
            'menu_name'     => 'Books',
            'add_new'       => 'Add New Book',
            'add_new_item'  => 'Add New Book',
            'new_item'      => 'New Book',
            'edit_item'     => 'Edit Book',
            'view_item'     => 'View Book',
            'all_items'     => 'All Books',
        ),
        'public' => true,
        'has_archive' => true,
        'show_in_rest' => true,
        'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt' ),
    );

    register_post_type( 'book', $args );
}

Now, browse to your WordPress dashboard and activate the plugin.

You should see a new menu item called “Books” in the admin menu with the ability to add new books to your book custom post type.

If you browse to the wp_posts table in the WordPress database, you’ll see a new row with the post_type column set to book, containing the new book data.