Question

I have a Rails 3 app that I am turning into a Rails engine / gem.
This engine has some gem dependencies that I have put inside it’s .gemspec file.

I have created a new ‘parent’ Rails 3 app, and I would like to add my engine gem to the Gemfile and have the gem’s dependencies automatically ‘loaded’, but this does not work for me! bundle install installs the gem dependencies fine, but when I start the server, the app crashes because they are not loaded.

For example, my engine’s gemspec contains these lines:

s.add_runtime_dependency(%q<rails>, ["= 3.0.7"])
s.add_runtime_dependency(%q<acts_as_commentable>, [">= 3.0.1"])
s.add_runtime_dependency(%q<haml>, [">= 3.1.1"])

.. and the parent Rails 3 application has these lines in its Gemfile:

source 'http://rubygems.org'

gem 'my_engine', :path => "~/src/gems/my_engine"

But I get the following error:

undefined local variable or method `acts_as_commentable'
from /home/user/src/gems/my_engine/app/models/account.rb:66:in `<class:Account>'

But if I add gem 'acts_as_commentable', '>= 3.0.1' to the Gemfile of the parent Rails 3 app, then the gem is loaded and the error disappears.

I am using Rails 3.0.8.

Does anyone have any suggestions? Do I need to change something about the way my engine is loading?

Answer 1

During main Rails app boot, Bundler will only require dependencies directly listed in the Gemfile but not any sub-dependencies. It’s your library’s/Engine’s responsibility to require its dependencies when it itself gets required. You can do so using initializers in your Railtie.

class MyRailtie < Rails::Railtie
  initializer "require stuff" do
    require "stuff"
  end
end