Polyamorous is an extraction from MetaSearch 1.1.x, Ransack, and Squeel by Ernie Miller.
If you are using Polyamorous with Rails 4.1, you'll need the latest commits in the git repo that are not yet in the official gem release. In your Gemfile:
gem 'polyamorous', github: 'activerecord-hackery/polyamorous'
Copyright © 2011-2014 Ernie Miller