Supermodel is a new library by Alex Maccaw that uses the Rails 3.0 ActiveModel library to provide ActiveRecord-esque in-memory "database" storage in Ruby.

Supermodel is best demonstrated with a basic example:

require 'supermodel'

class Person < SuperModel::Base; end

a = Person.new( :name => "Jim" )
a.save

Person.find_by_name('Jim') # => #<Person>
Person.all # => [#<Person>]

This is just the start! Out of the box, Supermodel supports validations, callbacks, observers, dirty change tracking, and serialization. It also allows you, with only a little magic, to go beyond ephemeral memory-only structures and marshall your SuperModel-based objects to disk or even to a Redis store.

A more complex example that includes randomly generated IDs and validations:

require 'supermodel'

class Person < SuperModel::Base
  include SuperModel::RandomID
  attributes :name
  validates_presence_of :name
end

a = Person.new
a.valid? # => false
a.name = "Jim"
a.valid? # => true
a.save
a.id # => "6481a4fcd834e567836587c6da"

It's early days for Supermodel, but I can see it becoming a big deal for Rubyists away from the Rails stack. The gemified version doesn't have support for relationships yet, but the edge version on GitHub has early support for belongs_to and has_many included.Alex has written the code in a well structured way and creating modules or subclasses to add support for interacting with other backends (such as, say, Tokyo Cabinet) doesn't look like it'd be too hard.

Supermodel shows a lot of promise and is what I was originally hoping ActiveModel was going to be. It provides just the right level of abstraction and separation from the database, but without losing the goodness we came to enjoy from ActiveRecord over the past few years.