How to do the following in case of Ruby on rails

How to do the following in case of Ruby on rails

How to do subdomains & seperated databases for a rails app as shown in
tutorial below for php
i am a newbie to to rails & ruby as well so i would like now that is any
thing possible which shown in this tutorial by anatgarg in php
1.subdomains 2.multiples databases 3.database switching based on subdomain