I’m using Devise + the omniauth-facebook gem to log in to my Rails 3 app using Facebook (see Rails 3 using Devise: How to allow someone to log in using their Facebook account?).
But how can I work with the Graph/OpenGraph API once authenticated? Use another gem such as Koala?
You could use a gem, or just treat it “RESTFully”. Check out some useful docs from Heroku.
There’s a similar question to yours too: Facebook Graph API gem