An excerpt from http://www.sitepoint.com/enumerated-types-with-activerecord-and-postgresql/, by @hendrauzia
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An Enumerated Type (also called an “enum”) is a data type with a set of named elements, each of them having a different value that can be used as constants, among other things. An enum can be implemented in various languages and frameworks, and in this article we will implement an enum in a Ruby on Rails application.
Rails, as you likely know, is an open source MVC web application framework. The M in MVC is ActiveRecord, which is an Object Relational Mapping Framework. ActiveRecord gives us the ability to represent models, their data, and other database operations in an object-oriented fashion. An enum is treated specially in ActiveRecord, being implemented using the ActiveRecord::Enum module.
Rails provides a very good usage of ActiveRecord::Enum, and to have a better architecture, we need to use it with the PostgreSQL Enumerated Type. Unfortunately, there is little or no mention on how to integrate these technologies. There’s even a statement that says it has no special support for enumerated types, although it is possible.
In this article, we’ll go over how to use PostgreSQL Enumerated Types with ActiveRecord::Enum.
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