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

I'm doing an engine here, it works alright in stand alone.

When I transform it into a gem, and load it inside another application, I get a lot of undefined errors, coming from my engine gem's dependecies.

Here is the gemspec:

s.add_dependency('paperclip')
s.add_dependency('jquery-rails')
s.add_dependency('rails3-jquery-autocomplete')
s.add_dependency('remotipart')
s.add_dependency('cancan')

In the application, when I do a bundle install, it lists all these dependencies, but as i run the application I receive a lot of undefined methods errors (has_attachment from paperclip for example). It seems that the application doesn't load the engines dependencies. Is this the default behavior? Can I change it? Same thing happened with a plugin inside the engine.

If I insert by hand those gems, in the application Gemfile, all works...

Include them in your gemfile and run bundle install. Then require them in your lib/<your_engine>/engine.rb file. Don't forget to require rubygems

  require 'rubygems'
  require 'paperclip'
  require 'jquery-rails'
  require 'rails3-jquery-autocomplete'
  require 'remotipart'
  require 'cancan'

Then in your host app (The app where you included your gem) run bundle install/ bundle update (bundle update did the trick for me) and then everything should work perfectly. You can also test this by starting the console in your host app and just type the module name e.g.

Loading development environment (Rails 3.0.3)
irb(main):001:0> Paperclip
=> Paperclip

Hope this helps

You can require them manually like Daniel posted, and you can also require them automatically. You need to add dependencies in 3 files:

• yourengine.gemspec

  s.add_dependency "rails", '4.1.0'
  s.add_dependency "sqlite3"
  

• Gemfile

  # Imports dependencies from yourengine.gemspec
  gemspec
  

• lib/yourengine.rb

  # requires all dependencies
  Gem.loaded_specs['yourengine'].dependencies.each do |d|
   require d.name
  end
  
  require 'yourengine/engine'
  
  module Yourengine
  end
  

Update: It's a simplistic demonstration of how to require the dependencies. You should test it and filter unwanted items, for example: require d.name unless d.type == :development (thx @imsinu9)

from paperclip's README :

For Non-Rails usage:

class ModuleName < ActiveRecord::Base
  include Paperclip::Glue
  ...
end

I had the same issue and that fixed it for me.

You must add the gem file to both the .gemspec file, and your engine.rb file. In the .gemspec file it would be like: s.add_dependency "kaminari", "0.16.1"

In the engine.rb file at the top add: require "kaminari"

I think you also need to add the gem to the rails engine Gemfile and bundle install, but I'm not certain if you need it there.