Component-Based Rails Applications (#cobra)

What is it?

Cobra is a way to organize your rails application, imagine it like a new way for packaging your rails apps

These are my annotations based on work of @shageman and @benjaminleesmith from Pivotal

Baby steps

So lets start write some code!

bundle exec rails plugin new shopping --full --mountable -d sqlite3 --skip-test-unit --dummy-path=spec/dummy -B
cd shopping
bundle install

What are the first steps before go coding?

Edit your gemspec
Monkeypatch migrations
Load component dependency automatically

Editing your gemspec

No secrets here, fill in the field (don't forget to remove the TODO:)

Monkeypatch migrations

Here is a nice trick (okay, its a monkey patch, but really helps you save a lot of time), instead of install migrations of your engines and make your migrates / rollbacks, in production this can be useful, but during development is a PITA

So we monkey patch our engine so when the wrapper application runs rake db:migrate our engine's migrations are run too.

So, lets do it, in your lib/shopping/engine.rb, you go from this:

module Shopping
  class Engine < ::Rails::Engine
    isolate_namespace Shopping
  end
end

to this:

module Shopping
  class Engine < ::Rails::Engine
    isolate_namespace Shopping
    
    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
  end
end

easy hun, now you only need to rake db:migrate and db:rollback

Load component dependency automatically

You added a gem on your component.gemspec, runned bundle install and what, it raised an error on wrapper it was not found?!

Its because bundle just requires dependencies, in a non recursive way, so you need to load it.

Go to lib/component/engine.rb and add:

module Component
  class Engine < ::Rails::Engine
    initializer "require stuff" do
      require "add_gem"
    end
  end
end

Damm, everytime we add a new dependency we need to do this? And if we remove a gem, it will raise an error when we try to require it? How we do automatically?

Go to lib/component/engine.rb and instead of add the single dependency, add this:

module Component
  class Engine < ::Rails::Engine
    
    # Initialize engine dependencies on wrapper application
    Gem.loaded_specs["component_template"].dependencies.each do |d|
      begin
        require d.name
      rescue LoadError => le
        # Put exceptions here.
        raise le if d.name !~ /factory_girl_rails/
      end
    end
  end
end

Template

Hey, make this all the time, can be not so cool, #cobra is about development pleasure

Check out my wrapper template, theres a copy_template.sh to make your #cobra coding easier!

fernandes/cobra.md