eav_hashes

https://github.com/200proof/eav_hashes

eav_hashes allows you to to leverage the power of the EAV database model in the way you would expect to use it: a hash. Unlike other gems which require you to create a special model and/or define which attributes you want to have EAV behavior on (both of which defeat the purpose), all you need to do with eav_hashes is add one line to your model and create a migration. All the heavy lifting is done for you.