How to set default taxonomy (category) for custom post types in WP (ok)

https://stackoverflow.com/questions/19706742/how-to-set-default-taxonomy-category-for-custom-post-types-in-wp

Ví dụ 1:

<?php
class Photo {
  /**
   * Instance of Photo
   * @access protected
   * @var object $instance The instance of Photo.
   */
  private static $instance = null;
  /**
   * Photo constructor.
   * This is a private constructor to be used in getInstance method to do things in a singleton way
   * It's a good idea to leave this constructor empty and make `init` method public to use it outside of the class, which is a good thing for Unit Testing
   * @access private
   */
  private function __construct() {
    $this->init();
  }
  /**
   * Initialize the plugin.
   * You can make it public and use it outside of the class
   * @access private
   * @return void
   */
  private function init() {
    // It's possible to use one method to cover these and hook it to `init`. I just like the way using single purpose OOP methods.
    // Note the priorities
    add_action('init', [$this, 'register_cpt'], 10);
    add_action('init', [$this, 'register_gallery_cat_tax'], 11);
    add_action('init', [$this, 'insert_default_gallery_cat_term'], 12);
    // `save_post_{$post->post_type}` hook is used. Doc: https://developer.wordpress.org/reference/hooks/save_post_post-post_type/
    add_action('save_post_photo', [$this, 'set_default_gallery_cat'], 99, 2);
  }
  /**
   * Register `Photo` CPT and `gallery_cat` taxonomy to it
   * This should be done after `init`
   * @access public
   * @wp-hook init
   * @return void
   */
  public function register_cpt() {
    $labels = array(
      'name'               => 'Photos',
      'singular_name'      => 'Photo',
      'add_new'            => 'Add New',
      'add_new_item'       => 'Add New Photo',
      'edit_item'          => 'Edit Photo',
      'new_item'           => 'New Photo',
      'all_items'          => 'All Photos',
      'view_item'          => 'View Photo',
      'search_items'       => 'Search Photos',
      'not_found'          => 'No Photos found',
      'not_found_in_trash' => 'No Photos found in Trash',
      'parent_item_colon'  => '',
      'menu_name'          => 'Photography',
    );
    $args = array(
      'public'       => true,
      'show_in_menu' => true,
      'labels'       => $labels,
      'supports'     => array('title', 'editor', 'author', 'thumbnail', 'excerpt', 'comments'),
      'taxonomies'   => array('post_tag', 'gallery_cat'),
    );
    register_post_type('photo', $args);
  }
  /**
   * Register `gallery_cat` taxonomy
   * This should be done after registering CPT
   * @access public
   * @wp-hook init
   * @return void
   */
  public function register_gallery_cat_tax() {
    $labels = [
      'name'              => 'Gallery Categories',
      'singular_name'     => 'Gallery Category',
      'all_items'         => 'All Gallery Categories',
      'edit_item'         => 'Edit Category',
      'view_item'         => 'View Category',
      'update_item'       => 'Update Category',
      'add_new_item'      => 'Add New Category',
      'new_item_name'     => 'Category Name',
      'parent_item'       => 'Parent Category',
      'parent_item_colon' => 'Parent Category:',
      'search_items'      => 'Search Gallery Categories',
      'popular_items'     => 'Popular Categories',
    ];
    register_taxonomy(
      'gallery_cat',
      'photo',
      array(
        'labels'        => $labels,
        'show_ui'       => true,
        'show_tagcloud' => false,
        'hierarchical'  => true,
      )
    );
  }
  /**
   * Insert default gallery_cat
   * `default_{$taxonomy}` option is used to make this term as default `gallery_cat` term (non-removable)
   * @access public
   * @wp-hook init
   */
  public function insert_default_gallery_cat_term() {
    // check if category(term) exists
    $cat_exists = term_exists('default_gallery_cat', 'gallery_cat');
    if (!$cat_exists) {
      // if term is not exist, insert it
      $new_cat = wp_insert_term(
        'Default Gallery Name',
        'gallery_cat',
        array(
          'description' => 'This is your default gallery category',
          'slug'        => 'default_gallery_cat',
        )
      );
      // wp_insert_term returns an array on success so we need to get the term_id from it
      $default_cat_id = ($new_cat && is_array($new_cat)) ? $new_cat['term_id'] : false;
    } else {
      //if default category is already inserted, term_exists will return it's term_id
      $default_cat_id = $cat_exists;
    }
    // Setting default_{$taxonomy} option value as our default term_id to make them default and non-removable (like default uncategorized WP category)
    $stored_default_cat = get_option('default_gallery_cat');
    if (empty($stored_default_cat) && $default_cat_id) {
      update_option('default_gallery_cat', $default_cat_id);
    }
  }
  /**
   * Add an default `gallery_cat` taxonomy term for `photo` CPT on save
   * If no `gallery_cat` is selected, default gallery_cat will be registered to the post
   * @access public
   * @wp-hook save_post_photo
   * @param integer $post_id
   * @param object $post
   */
  public function set_default_gallery_cat($post_id, $post) {
    if ('publish' === $post->post_status) {
      $gallery_cats        = wp_get_post_terms($post_id, 'gallery_cat');
      $default_gallery_cat = (int) get_option('default_gallery_cat');
      if (empty($gallery_cats)) {
        wp_set_object_terms($post_id, $default_gallery_cat, 'gallery_cat');
      }
    }
  }
  /**
   * Instance
   * Used to retrieve the instance of this class.
   * @access public
   * @return object $instance of the class
   */
  static public function getInstance() {
    if (self::$instance == NULL) {
      self::$instance = new self();
    }
    return self::$instance;
  }
}
// Run this
Photo::getInstance();
?>

Ví dụ 2:

class Test {
	private static $instance = null;
	private function __construct() {
		$this->init();
	}
	private function init() {
		add_action('init', [$this, 'register_cpt'], 10);
		add_action('init', [$this, 'register_gallery_cat_tax'], 11);
		add_action('init', [$this, 'insert_default_gallery_cat_term'], 12);
		add_action('save_post_book', [$this, 'set_default_gallery_cat'], 99, 2);
	}
	public function register_cpt() {
		$args = array(
        'public'    => true,
        'label'     => __( 'Books', 'textdomain' ),
        'menu_icon' => 'dashicons-book',
    );
    register_post_type( 'book', $args );
	}
	public function register_gallery_cat_tax() {
		$args = array(
        'label'        => __( 'Genre', 'textdomain' ),
        'hierarchical' => true,
    );
		register_taxonomy( 'genre', 'book',  $args);
	}
	public function insert_default_gallery_cat_term() {
		$cat_exists = term_exists('default_genre', 'genre');
		if (!$cat_exists) {
			$new_cat = wp_insert_term(
        'Default Book',
        'genre',
        array(
          'description' => 'This is your default Book category',
          'slug'        => 'default_genre',
        )
      );
      $default_cat_id = ($new_cat && is_array($new_cat)) ? $new_cat['term_id'] : false;
		}else {
      $default_cat_id = $cat_exists;
		}
		$stored_default_cat = get_option('default_genre');
		if (empty($stored_default_cat) && $default_cat_id) {
			update_option('default_genre', $default_cat_id);
		}
	}
	public function set_default_gallery_cat($post_id, $post) {
		if ('publish' === $post->post_status) {
			$book_cats        = wp_get_post_terms($post_id, 'genre');
			$default_book_cat = (int) get_option('default_genre');
			if (empty($book_cats)) {
        wp_set_object_terms($post_id, $default_book_cat, 'genre');
      }
		}
	}
	public static function getInstance() {
		if(self::$instance == null) {
			self::$instance = new self();
		}
		return self::$instance;
	}
}
Test::getInstance();