Rails: Loading custom class from lib folder in controller

there is a setting in config/application.rb in which you can specify directories that contain files you want autoloaded.

From application.rb:

# Custom directories with classes and modules you want to be autoloadable.
# config.autoload_paths += %W(#{config.root}/extras)

or

config.autoload_paths += Dir["#{config.root}/lib/**/"]

rails 3

Dir["lib/**/*.rb"].each do |path|
  require_dependency path
end 

You probably need to enable the autoload from the files in the lib/ folder:

# config/application.rb
config.autoload_paths << "#{Rails.root}/lib"

If you prefer to do it "manually", then you can only require such file in the same file:

# config/application.rb
require './lib/my_service'

After this a restart is necessary.

Ruby on Rails expects certain naming conventions to support autoloading.

Rails can autoload a file located at lib/services/my_service.rb if the model/class structure was Services::MyService.

Change your lib/services/my_service.rb to:

module Services
  class MyService
    # ...
  end
end

And use that class like this in your controller:

service = Services::MyService.new

Please note that depending on your Ruby on Rails version you might need to add the lib folder to the list of folders which are queried when looking for a file to autoload:

# add this line to your config/application.rb:
config.autoload_paths << "#{Rails.root}/lib"

Read more about autoloading in the Rails Guides.