Question

In my rails3 engine gemfile, I added:

gem 'paperclip'
gem 'inherited_resources'

I also added this to my gemspec:

s.add_dependency "paperclip"
s.add_dependency "inherited_resources"

I then ran bundle install for both my engine and the client app and started up the console for the client app in order to first test paperclip, to which I get:

Using /Users/ynkr/.rvm/gems/ruby-1.9.2-p180 with gemset rails31beta
ynkr % rails c
/Users/ynkr/.rvm/gems/ruby-1.9.2-p180@rails31beta/gems/actionpack-3.1.0.rc4/lib/action_dispatch/http/mime_type.rb:101: warning: already initialized constant YML
Loading development environment (Rails 3.1.0.rc4)
ruby-1.9.2-p180 :001 > b=Blog::Blog.first 
  Blog::Blog Load (0.2ms)  SELECT `blogs`.* FROM `blogs` LIMIT 1
 => #<Blog::Blog id: 1, user_id: 1, context_id: 2, title: "Cmd Line Blog Title", title_for_url: "cmd-line-blog-title", teaser: "This is the teaser for the command line blog", content: "Some content for the cmd line blog", created_at: "2011-06-28 06:06:55", updated_at: "2011-06-28 06:06:55"> 
ruby-1.9.2-p180 :002 > b.photos
NoMethodError: undefined method `has_attached_file' for #<Class:0x00000102a57fc8>
    from /Users/ynkr/.rvm/gems/ruby-1.9.2-p180@rails31beta/gems/activerecord-3.1.0.rc4/lib/active_record/base.rb:1078:in `method_missing'
    from /websites/gems/blog/app/models/blog/photo.rb:6:in `<class:Photo>'
    from /websites/gems/blog/app/models/blog/photo.rb:1:in `<top (required)>'
    from /Users/ynkr/.rvm/gems/ruby-1.9.2-p180@rails31beta/gems/activesupport-3.1.0.rc4/lib/active_support/dependencies.rb:452:in `load'

OK, so it appears the has_attached_file method from the paperclip gem cannot be found. Why? I’m not sure.

Moving on to inherited_resources, I altered a scaffold generated controller to look like the following:

class Blog::ContextsController < InheritedResources::Base
  before_filter :redirect_unless_admin
end

and load up the index page for that to which I am greeted (in the logs) with:

Started GET "/blog/contexts" for 127.0.0.1 at 2011-06-28 12:06:25 -0700

ActionController::RoutingError (uninitialized constant InheritedResources):

Rendered /Users/ynkr/.rvm/gems/ruby-1.9.2-p180@rails31beta/gems/actionpack-3.1.0.rc4/lib/action_dispatch/middleware/templates/rescues/routing_error.erb within rescues/layout (0.5ms)

My question is why are these not working? My hunch is that there is something about engines, namespacing and loading up gems that I am totally unaware of.

Answer 1

You need to require each gem within your engine in an initializer file, eg. lib/<your_engine_name>/engine.rb

Bit more of an explanation over here…

Rails Engine – Gems dependencies, how to load them into the application?