我有一个自定义的帖子类型（收藏夹），我计划用它来谈论我最喜欢的工艺品。我想要的meta-box字段是指向在线商店列表的链接，因此用户可以自己购买产品，如果他们选择的话。

下面是自定义帖子类型和所需字段（本质上是一个文本框）的定义。

<?php

    function declare_custom_post_type() {
        $theme_name = \'thatannalam\';
        $custom_post_type = \'favourites\';

        $labels = array(
            \'name\'               => __(\'Favourites\', $theme_name),
            \'singular_name\'      => __(\'Favourite\', $theme_name),
            \'add_new\'            => __( \'Add New Favourite\' ),
            \'add_new_item\'       => __( \'Add New Favourite\' ),
            \'edit_item\'          => __( \'Edit Favourite\' ),
            \'new_item\'           => __( \'Add New Favourite\' ),
            \'view_item\'          => __( \'View Favourite\' ),
            \'search_items\'       => __( \'Search EvFavouriteent\' ),
            \'not_found\'          => __( \'No favourites found\' ),
            \'not_found_in_trash\' => __( \'No favourites found in trash\' )
        );

        $args = array(
            \'description\' => __( \'Movie news and reviews\', $theme_name),
            \'exclude_from_search\' => false,
            \'labels\' => $labels,
            \'has_archive\' => true,
            \'hierarchical\' => false,
            \'public\' => true,
            \'register_meta_box_cb\' => \'register_meta_box\',
            \'rewrite\' => array(\'slug\', $custom_post_type),
            \'show_in_admin_bar\' => true,
            \'show_in_menu\' => true,
            \'show_in_nav_menus\' => true,
            \'show_in_rest\' => true,
            \'show_ui\' => true,
            \'supports\' => array(\'title\', \'editor\', \'custom-fields\')
        );

        register_post_type($custom_post_type, $args);
    }
    add_action(\'init\', \'declare_custom_post_type\');

    function register_meta_box() {
        add_meta_box(
            \'favourite_details_box\',
            \'Favourite Details\',
            \'render_meta_html\',
            \'favourites\',
            \'side\'
        );
    }

    function render_meta_html() {
        global $post;
        $nonce_key = \'favourite_fields_nonce\';
        $link_meta_key = \'product_link_key\';

        wp_nonce_field($nonce_key, $nonce_key);

        $link = get_post_meta( $post->ID, $link_meta_key, true );
        echo \'<label for="product_link_field" class="widefat">Product Link</label><input type="text" id="product_link_field" name="product_link_field" class="widefat" value="\'.$link.\'">\';
    }

    function save_favourite_meta($post_id, $post) {
        $nonce_key = \'favourite_fields_nonce\';
        $link_meta_key = \'product_link_key\';
        $link_field_name = \'product_link_field\';
        $custom_post_type = \'favourites\';

        // verify nonce
        if (!isset($_POST[$nonce_key]) || !wp_verify_nonce($_POST[$nonce_key], $nonce_key))
            return \'nonce not verified\';

        // check autosave
        if (wp_is_post_autosave($post_id ))
            return \'autosave\';

        //check post revision
        if (wp_is_post_revision($post_id))
            return \'revision\';

        // check permissions
        if ( ! current_user_can( \'edit_post\', $post_id ) ) {
            return \'cannot edit post\';
        }

        $product_link = $_POST[$link_field_name];
        
        if (metadata_exists($custom_post_type, $post_id, $link_meta_key)) {
            update_post_meta($post_id, $link_meta_key, $product_link);
        } else {
            add_post_meta($post_id, $link_meta_key, $product_link);
        }
    }

    add_action( \'save_post\', \'save_favourite_meta\');
?>

检索保存的值。它当前返回一个空白