Problem creating Rails 3 Engine

Question

I'm working on creating my first Rails 3 engine and I'm currently getting the following error message

is a Railtie/Engine and cannot be installed as plugin (RuntimeError)

To give you a bit more background I'm not doing the Engine as a gem, but I've place the Engine files in the vendor/plugins folder. I know there is an issue with loading when in the plugins folder, but I'm not clear on how to solve the problem.

My rails/init.rb file in the Engine has the following code

require 'rails'

module RailsApp
  module MyEngine
    class Engine < Rails::Engine

      config.after_initialize do
        RailsApp::GameType.register do |game_type|
          game_type.name = "TreasureIsland"
          game_type.version = "0.1"
          game_type.thumbnail = "teasure_island.jpg"
        end
      end
    end
  end
end

Suggestions?

Answer 1

I think I remember reading that Railties would not work in plugins directory, because they are intended to be loaded at a different point in the application boot process. I would recommend creating a gem using something like Jeweler, which does alot of the work for you. The purpose of the Railtie/Engine is to have a reusable component that can be included in multiple rails apps. Once you have a gem created, you can point to the local gem path within your Gemfile. This allows you to see changes in your engine code inside your rails app without having to build and reinstall the gem every time you make a change to the engine code. Of course you would want to point bundler to the installed gem in production. I would recommend putting it on github and using that URL in your Gemfile in production.

Bundler local gem example:

#Gemfile
gem "my_engine", :require => "my_engine", :path => "/my_engines/my_engine"

Check out the Modern Rubyist's website. He has a good series on creating Railties and Engines. There may have been some changes to Rails since this was written, but I think most of it is still relevant. It helped me out a good bit when I was learning how to write Engines with Rails 3.

http://www.themodestrubyist.com/2010/03/01/rails-3-plugins---part-1---the-big-picture/
http://www.themodestrubyist.com/2010/03/05/rails-3-plugins---part-2---writing-an-engine/
http://www.themodestrubyist.com/2010/03/16/rails-3-plugins---part-3---rake-tasks-generators-initializers-oh-my/
http://www.themodestrubyist.com/2010/03/22/rails-3-plugins---part-4---more-on-generators/

Answer 2

John, I believe engines (which are typically gems) vs plugins (which live in vendor) are loaded at different points in the rails initialization process.

Engines actually have a bit more flexibility, they can hook deeper into rails. In addition, packaging as a gem has a lot of advantages: easier to share across apps, easier to maintain in a separate code repo, easier version control.

I'm creating my first rails engine right now and created a useful starting point and walk-through for getting started:

http://keithschacht.com/creating-a-rails-3-engine-plugin-gem/