Code Samples: Setting Default Taxonomy Term for Custom Taxonomy & Custom Post Type

Here’s a clever way to set to the default Custom Taxonomy Term for a Post Type (similar to ‘Uncategorized’ in Posts)

/**
* Author: Michael Fields
* Source: http://wordpress.mfields.org/2010/set-default-terms-for-your-custom-taxonomies-in-wordpress-3-0/
* Thanks a lot for the nice tweak
*/


/**
 * Define default terms for custom taxonomies in WordPress 3.0.1
 *
 * @author    Michael Fields     http://wordpress.mfields.org/
 * @props     John P. Bloch      http://www.johnpbloch.com/
 *
 * @since     2010-09-13
 * @alter     2010-09-14
 *
 * @license   GPLv2
 */
function mfields_set_default_object_terms( $post_id, $post ) {
    if ( 'publish' === $post->post_status ) {
        $defaults = array(
            'post_tag' => array( 'taco', 'banana' ),
            'monkey-faces' => array( 'see-no-evil' ),
            );
        $taxonomies = get_object_taxonomies( $post->post_type );
        foreach ( (array) $taxonomies as $taxonomy ) {
            $terms = wp_get_post_terms( $post_id, $taxonomy );
            if ( empty( $terms ) && array_key_exists( $taxonomy, $defaults ) ) {
                wp_set_object_terms( $post_id, $defaults[$taxonomy], $taxonomy );
            }
        }
    }
}
add_action( 'save_post', 'mfields_set_default_object_terms', 100, 2 );

/**
* Just change the 'post_tag' with the taxonomy slug you want to target
* and change 'taco' and 'banana' with the slug of the term you want to make default
* you can add multiple taxonomy at once so the line#19 is applicable only then
*/