Keep your migrations in the engine

via: http://blog.pivotal.io/labs/labs/leave-your-migrations-in-your-rails-engines

in lib/[engine_name]/engine.rb

initializer :append_migrations do |app|
  unless app.root.to_s.match root.to_s
    config.paths["db/migrate"].expanded.each do |expanded_path|
      app.config.paths["db/migrate"] << expanded_path
    end
  end
end

Decorators, inputs, etc.

in lib/[engine_name]/engine.rb

root = File.expand_path('../../', __FILE__)
config.autoload_paths << root

config.to_prepare do
  Dir[File.join(root, "../app/decorators/**/*_decorator*.rb")].each do |c|
    require_dependency(c)
  end
end

Testing with RSpec

in spec/rails_helper.rb

# This file is copied to spec/ when you run 'rails generate rspec:install'
ENV['RAILS_ENV'] ||= 'test'
require 'spec_helper'
require File.expand_path("../dummy/config/environment.rb",  __FILE__)
require 'rspec/rails'
# Add additional requires below this line. Rails is not loaded until this point!

ENGINE_RAILS_ROOT=File.join(File.dirname(__FILE__), '../')
# Requires supporting ruby files with custom matchers and macros, etc,
# in spec/support/ and its subdirectories.
Dir[File.join(ENGINE_RAILS_ROOT, "spec/support/**/*.rb")].each {|f| require f }

Links

• http://guides.rubyonrails.org/engines.html
• http://guides.rubyonrails.org/generators.html
• http://tech.taskrabbit.com/blog/2014/02/11/rails-4-engines/
• http://www.toptal.com/ruby-on-rails/rails-engines-in-the-wild-real-world-examples-of-rails-engines-in-action
• http://brandonhilkert.com/blog/how-to-build-a-rails-engine/
• https://teamgaslight.com/blog/maintainable-and-scalable-systems-with-rails-engines
• http://asciicasts.com/episodes/277-mountable-engines