Extracting a Rails application into a plugin or engine

Question

I have a Rails 2.3 application which I would like to extract into a plugin, or engine. The application has user authentication, and basic cms capabilities supported by ancestry plugin.

I want to extract the logic for the application into a plugin/engine so that I can use this code for future projects, with a different "skin" or "theme" if required.

I'm not entirely sure I actually understand the difference between plugin and engine concepts, so that would be a good first point.

What is the best approach, are there any good starting points, links, explanations, examples that I should follow. Also, with the release of R3 to consider, is there anything that I should be aware of for that, with regards to plugins etc.

I am going to start off by watching Ryan's http://railscasts.com/episodes/149-rails-engines but obviously thats over a year old now, so one of the challenges I'm faced with is finding the most up to date and relevant information on this subject.

All tips and help gratefully received.

Answer 1

Actually, converting an application is pretty straigtforward. Just create a plugin-folder, put an app-folder inside containing all yor model-views-controllers folders, and that's it.

You will have to manage your migrations yourself though. Also you have to define rake-tasks to copy files to your public folder. I think the railscasts is still pretty up-to-date, if anything it is now easier in rails 2.3.

Good luck!

[EDIT: for rails3] Rails 3 engines are very clean and powerful. Check this gist by Jose Valim.

Answer 2

You will probably be better off focusing your engine on Rails 3, as opposed to trying to make it compatible for Rails 2 and Rails 3, due to the backwards incompatible changes. Here is a more up to date tutorial for Rails 3

also the book "Crafting Rails applications" by Rails Core member Jose Valim, has a good chapter on it. Int he shows how to use his tool EngineX which generates a Rails 3 engine structure, so you can more easily create engines for your Rails 3 projects. His gem devise is also a rails engine which is also nice, because you can easily customize it by copying the templates into the application directory, and allowing you to subclass the controllers that you want to customize more.