I don't know if the DBIx::Class ORM is substantial enough to justify an entire book on the subject but I'd like to get a recommendation for a book that goes into the details of the DBIx::Class ORM.
I don't know if you can do much better than the online documentation. Between the introduction, walkthrough example, and cookbook, I think you'll have all you need to get started. Once you've looked through those, most of what you'll need for working with the ORM can be found in the ResultSet pod.
If you're really looking for a book, Jonathan Rockaway's Catalyst has a few chapters on setting up a DBIx-Class model. Obviously, most of that book is going to be irrelevant unless you're writing a Catalyst web app.