should a non-database data class I need be created as a Rails 3 "model", or just a basic class in the /lib area?
I want to build some classes to represent calculated domain objects. So the fields won't reference a database table/column. There will be also methods in the class that with the data.
Question - When generating these classes should these be just normal Ruby classes I put in the /lib area? Or should I/can I use rails models for this (and generate with "rails g model ...")?
Tableless models should probably be kept in app/models. I have several that access APIs. ActiveModel in Rails can help bring in some of the useful functionality of Active Record.
Interesting question..I had the same question a few weeks back.
I put those class under model directory. This is how I came up with that decision. The class that I wrote was completely related to a particular app no common features to share with anyone at-least at the moment. I also needed to use some of my existing models to query some data in that class. So I made it a class under model directory. I might be wrong but thats what I have done now.
In another case where I am using a certain api sets for a web and mobile app I am thinking of making the code which interfaces with the api into a gem. The thing to note here is that the api set is also part my system and it will only be used by my apps.
Classes that don't map to database tables can still reside inside of app/models. Instead of extending your class from ActiveRecord::Base, you can simply declare your class without any extensions (or your own extensions).
The CanCan ability model is a good example of this. It resides in app/models/, however does not extend ActiveRecord::Base. More information on CanCan's ability model can be found here: https://github.com/ryanb/cancan/wiki/Defining-Abilities
Also consider that code under lib/ will not reload in the development environment by default.
