How to do the following in case of Ruby on Rails

How to do subdomains & separated databases for a rails app as shown in tutorial below for PHP.

I am a beginner with Ruby & Ruby on Rails 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

1. You can see screencasts @ Railscasts episode #221 Subdomains in Rails 3
2. Actually, I never use multiples databases, but I have try use multiples schemas with postgresql, see @ Railscasts episode #389 Multitenancy with PostgreSQL pro
3. You can use gem apartment for switching schema based on subdomain

I can't explain one by one because it would be too long to be explained.