Sometimes we need to build an application that has domain models that we don’t know all the attributes of. A good example of such application is a system for tracking business contacts. In the center of it is a Contact model that has attributes like name, email, phone number, etc. But can we know beforehand all the attributes that our Contact model will need to have? If we want to create the application for a wide audience, it can be difficult to predict. Solution? Allow users to add more attributes to Contact model in the runtime! We’ll do exactly that in this tutorial.

https://medium.com/@koss_lebedev/how-to-dynamically-add-attributes-to-your-activerecord-models-e233b17ad695#.aahh3m3yd