SEO friendly routing

Hi all!

I’m moving to Ruby on Rails from PHP/ZendFramework. And i cannot
understand how to make such routing model:

I am trying to develop articles site from scratch, so i have article
model with fields: id, title, section, alias and body, also i have
sections tree for navigation, each section has fields: id, parent_id,
title, alias.

I want to have each article have path like
{root_section_alias}/{subsection_alias}/{article_alias}

Example urls:

http://localhost/news/spb/ramstain-rullezz
http://localhost/humor/some-humor-article


Excuse for my bad English

Try the plugin at GitHub - smsohan/acts_as_permalinkable: A ruby on rails ActiveRecord plugin for using search engine (SEO) friendly permalink style URLs