问WP Rest API返回所有自定义分类标题

EN

    add_action( 'rest_api_init', 'register_book_type' );
function register_book_type() {
    register_rest_field( 'lesson',
        'book_type',
        array(
            'get_callback'    => 'get_book_type',
            'update_callback' => null,
            'schema'          => null,
        )
    );
}
function get_book_type( $object, $field_name, $request ) {
    $name = [];
    $object = get_terms(array(
      'taxonomy' => 'book_type'
    ));
    foreach ($object as $term) :
      array_push($name, $term->name.' ');
    endforeach;
    return implode('/ ', $name);
}