Yeah, I have considered it. For reasons, I prefer simple integer approach rather than enum.

 - Enum is implemented differently in different database
 - [Enum is evil in some database, like MySQL](http://komlenic.com/244/8-reasons-why-mysqls-enum-data-type-is-evil/)

In case like this, I prefer simple and easy to control approach. However, as we only use PostgreSQL in production environment, if it is less error-prone or have some other benefits, I can switch to enum type then.