您可以通过rest_prepare_{$this->post_type} 过滤器，类似于自定义帖子类型的过滤器test_cpt （注册于hierarchical 和show_in_rest 设置为true):

add_filter( \'rest_prepare_test_cpt\', \'rest_prepare_test_cpt\' );
function rest_prepare_test_cpt( WP_REST_Response $response ) {
    $data = $response->get_data();

    if ( ! empty( $data[\'parent\'] ) ) {
        if ( ! $parent_post = get_post( $data[\'parent\'] ) ) {
            return $response;
        }

        // Include only some post data.
        $data[\'parent_data\'] = [
            \'title\'   => get_the_title( $parent_post ),   // or just $parent_post->post_title
            \'excerpt\' => get_the_excerpt( $parent_post ), // or just $parent_post->post_excerpt
            \'link\'    => get_permalink( $parent_post ),
        ];

        // Or include the whole data..
        // $data[\'parent_data\'] = $parent_post;             // object
        // $data[\'parent_data\'] = $parent_post->to_array(); // array

        $response->set_data( $data );
    }

    return $response;
}

请注意，如果设置不同的rest_controller_class 注册帖子类型时。（默认控制器类为WP_REST_Posts_Controller 触发上面使用的过滤器）