Heroku recently released hstore, a seamless key value pair that can be used in Rails 4. This tool is used in the relational database PostgreSQL. The creator compares this to hashes in Ruby. Since hstore is a native data type, it promotes faster querying. According to the video's creator, you'll need the most recent copy of Postgres in order to use this. He also provides you with a walkthrough of the hstore demo provided by Heroku.
You can find all the code necessary for getting started by heading over to Sheems blog.