I'm working on a new book - Advanced Active Record! It's going to be a practitioner's handbook with short but punchy bits on associations, scopes, migrations, Arel, and all that sort of thing. Please sign up on the book's page to get notified when it's ready to roll. Or you can email me or hit me up on the twitters. And let me know if there's anything in particular you'd like discussed in the book. Thanks!