I’m going to be talking about the DRY principle next week. However, before I jump into that, I need to discuss how to extend Ruby on Rails so you know where you can put functionality to keep your application DRY.

There are a couple of standard places people put code that isn’t a Model, View, Controller, or Helper:

The ‘lib’ folder - This is sort of a “junk drawer” for your application. In Rails 3 your application does not load these files on its own. You can make it autoload by following the directions I found on StackOverflow.

Rails Plugins - Rails Plugins are autoloaded by your Rails applications and can contain extensions to Models, Views, Controllers, Helpers, and to the app as a whole through Engines.

Ruby Gems - Gems can do pretty much anything Plugins can do except they are not included in your application’s source. They are pulled in through Bundler.

You can also add modules and classes to files within the app directory.