Use the conditional tag post_type_exists() to check if the post type book exists, if it exists add taxonomy to it otherwise not
<?php
if( post_type_exists( 'book' ){
add_action( 'init', 'create_book_taxonomies' );
// create two taxonomies, genres and writers for the post type "book"
function create_book_taxonomies() {
// Add new taxonomy, make it hierarchical (like categories)
$labels = array(
'name' => _x( 'Genres', 'taxonomy general name', 'textdomain' ),
'singular_name' => _x( 'Genre', 'taxonomy singular name', 'textdomain' ),
'search_items' => __( 'Search Genres', 'textdomain' ),
'all_items' => __( 'All Genres', 'textdomain' ),
'parent_item' => __( 'Parent Genre', 'textdomain' ),
'parent_item_colon' => __( 'Parent Genre:', 'textdomain' ),
'edit_item' => __( 'Edit Genre', 'textdomain' ),
'update_item' => __( 'Update Genre', 'textdomain' ),
'add_new_item' => __( 'Add New Genre', 'textdomain' ),
'new_item_name' => __( 'New Genre Name', 'textdomain' ),
'menu_name' => __( 'Genre', 'textdomain' ),
);
$args = array(
'hierarchical' => true,
'labels' => $labels,
'show_ui' => true,
'show_admin_column' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'genre' ),
);
register_taxonomy( 'genre', array( 'book' ), $args );
// Add new taxonomy, NOT hierarchical (like tags)
$labels = array(
'name' => _x( 'Writers', 'taxonomy general name', 'textdomain' ),
'singular_name' => _x( 'Writer', 'taxonomy singular name', 'textdomain' ),
'search_items' => __( 'Search Writers', 'textdomain' ),
'popular_items' => __( 'Popular Writers', 'textdomain' ),
'all_items' => __( 'All Writers', 'textdomain' ),
'parent_item' => null,
'parent_item_colon' => null,
'edit_item' => __( 'Edit Writer', 'textdomain' ),
'update_item' => __( 'Update Writer', 'textdomain' ),
'add_new_item' => __( 'Add New Writer', 'textdomain' ),
'new_item_name' => __( 'New Writer Name', 'textdomain' ),
'separate_items_with_commas' => __( 'Separate writers with commas', 'textdomain' ),
'add_or_remove_items' => __( 'Add or remove writers', 'textdomain' ),
'choose_from_most_used' => __( 'Choose from the most used writers', 'textdomain' ),
'not_found' => __( 'No writers found.', 'textdomain' ),
'menu_name' => __( 'Writers', 'textdomain' ),
);
$args = array(
'hierarchical' => false,
'labels' => $labels,
'show_ui' => true,
'show_admin_column' => true,
'update_count_callback' => '_update_post_term_count',
'query_var' => true,
'rewrite' => array( 'slug' => 'writer' ),
);
register_taxonomy( 'writer', 'book', $args );
}
}
Or if you haven’t created post type book yet, you can do so as:
/**
* Register a custom post type called "book".
*
* @see get_post_type_labels() for label keys.
*/
function wpdocs_codex_book_init() {
$labels = array(
'name' => _x( 'Books', 'Post type general name', 'textdomain' ),
'singular_name' => _x( 'Book', 'Post type singular name', 'textdomain' ),
'menu_name' => _x( 'Books', 'Admin Menu text', 'textdomain' ),
'name_admin_bar' => _x( 'Book', 'Add New on Toolbar', 'textdomain' ),
'add_new' => __( 'Add New', 'textdomain' ),
'add_new_item' => __( 'Add New Book', 'textdomain' ),
'new_item' => __( 'New Book', 'textdomain' ),
'edit_item' => __( 'Edit Book', 'textdomain' ),
'view_item' => __( 'View Book', 'textdomain' ),
'all_items' => __( 'All Books', 'textdomain' ),
'search_items' => __( 'Search Books', 'textdomain' ),
'parent_item_colon' => __( 'Parent Books:', 'textdomain' ),
'not_found' => __( 'No books found.', 'textdomain' ),
'not_found_in_trash' => __( 'No books found in Trash.', 'textdomain' ),
'featured_image' => _x( 'Book Cover Image', 'Overrides the “Featured Image” phrase for this post type. Added in 4.3', 'textdomain' ),
'set_featured_image' => _x( 'Set cover image', 'Overrides the “Set featured image” phrase for this post type. Added in 4.3', 'textdomain' ),
'remove_featured_image' => _x( 'Remove cover image', 'Overrides the “Remove featured image” phrase for this post type. Added in 4.3', 'textdomain' ),
'use_featured_image' => _x( 'Use as cover image', 'Overrides the “Use as featured image” phrase for this post type. Added in 4.3', 'textdomain' ),
'archives' => _x( 'Book archives', 'The post type archive label used in nav menus. Default “Post Archives”. Added in 4.4', 'textdomain' ),
'insert_into_item' => _x( 'Insert into book', 'Overrides the “Insert into post”/”Insert into page” phrase (used when inserting media into a post). Added in 4.4', 'textdomain' ),
'uploaded_to_this_item' => _x( 'Uploaded to this book', 'Overrides the “Uploaded to this post”/”Uploaded to this page” phrase (used when viewing media attached to a post). Added in 4.4', 'textdomain' ),
'filter_items_list' => _x( 'Filter books list', 'Screen reader text for the filter links heading on the post type listing screen. Default “Filter posts list”/”Filter pages list”. Added in 4.4', 'textdomain' ),
'items_list_navigation' => _x( 'Books list navigation', 'Screen reader text for the pagination heading on the post type listing screen. Default “Posts list navigation”/”Pages list navigation”. Added in 4.4', 'textdomain' ),
'items_list' => _x( 'Books list', 'Screen reader text for the items list heading on the post type listing screen. Default “Posts list”/”Pages list”. Added in 4.4', 'textdomain' ),
);
$args = array(
'labels' => $labels,
'public' => true,
'publicly_queryable' => true,
'show_ui' => true,
'show_in_menu' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'book' ),
'capability_type' => 'post',
'has_archive' => true,
'hierarchical' => false,
'menu_position' => null,
'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'comments' ),
);
register_post_type( 'book', $args );
}
add_action( 'init', 'wpdocs_codex_book_init' );
add_action( 'init', 'create_book_taxonomies' );
// create two taxonomies, genres and writers for the post type "book"
function create_book_taxonomies() {
// Add new taxonomy, make it hierarchical (like categories)
$labels = array(
'name' => _x( 'Genres', 'taxonomy general name', 'textdomain' ),
'singular_name' => _x( 'Genre', 'taxonomy singular name', 'textdomain' ),
'search_items' => __( 'Search Genres', 'textdomain' ),
'all_items' => __( 'All Genres', 'textdomain' ),
'parent_item' => __( 'Parent Genre', 'textdomain' ),
'parent_item_colon' => __( 'Parent Genre:', 'textdomain' ),
'edit_item' => __( 'Edit Genre', 'textdomain' ),
'update_item' => __( 'Update Genre', 'textdomain' ),
'add_new_item' => __( 'Add New Genre', 'textdomain' ),
'new_item_name' => __( 'New Genre Name', 'textdomain' ),
'menu_name' => __( 'Genre', 'textdomain' ),
);
$args = array(
'hierarchical' => true,
'labels' => $labels,
'show_ui' => true,
'show_admin_column' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'genre' ),
);
register_taxonomy( 'genre', array( 'book' ), $args );
// Add new taxonomy, NOT hierarchical (like tags)
$labels = array(
'name' => _x( 'Writers', 'taxonomy general name', 'textdomain' ),
'singular_name' => _x( 'Writer', 'taxonomy singular name', 'textdomain' ),
'search_items' => __( 'Search Writers', 'textdomain' ),
'popular_items' => __( 'Popular Writers', 'textdomain' ),
'all_items' => __( 'All Writers', 'textdomain' ),
'parent_item' => null,
'parent_item_colon' => null,
'edit_item' => __( 'Edit Writer', 'textdomain' ),
'update_item' => __( 'Update Writer', 'textdomain' ),
'add_new_item' => __( 'Add New Writer', 'textdomain' ),
'new_item_name' => __( 'New Writer Name', 'textdomain' ),
'separate_items_with_commas' => __( 'Separate writers with commas', 'textdomain' ),
'add_or_remove_items' => __( 'Add or remove writers', 'textdomain' ),
'choose_from_most_used' => __( 'Choose from the most used writers', 'textdomain' ),
'not_found' => __( 'No writers found.', 'textdomain' ),
'menu_name' => __( 'Writers', 'textdomain' ),
);
$args = array(
'hierarchical' => false,
'labels' => $labels,
'show_ui' => true,
'show_admin_column' => true,
'update_count_callback' => '_update_post_term_count',
'query_var' => true,
'rewrite' => array( 'slug' => 'writer' ),
);
register_taxonomy( 'writer', 'book', $args );
// Following code will assign default taxonomy to genre taxonomy
if( !term_exists( 'intelligence', 'genre' ) ){
$parent_term = term_exists( 'genre', 'genre' );
wp_insert_term(
'Intelligence',
'genre',
array(
'description'=> 'Book about Intelligence',
'slug' => 'intelligence',
'parent'=> $parent_term['term_id']
)
);
}
}
I have tested this code and it works, it should work for you as well
If you want to add your custom taxonomies to wordpress post then use:
register_taxonomy( 'writer', array( 'book', 'post' ), $args );