37signals Dev — Vanilla Rails is plenty

The seminal Domain Driven Design (DDD) book discusses these four conceptual layers: presentation, application, domain, and infrastructure. The application layer implements business tasks by coordinating work with the domain layer. But Rails only offers controllers and models: models include persistence via Active Record, and Rails encourages direct access to them from controllers. Critics argue that the application, domain, and infrastructure layers inevitably merge into a single mess of fat models. Indeed, alternatives always include additional buckets, such as services or use case interactors, at the application layer, or repositories, at the infrastructure layer.