Virtus

This is a partial extraction of the DataMapper Property API with various modifications and improvements. The goal is to provide a common API for defining attributes on a model so all ORMs/ODMs could use it instead of reinventing the wheel all over again. It is also suitable for any other usecase where you need to extend your ruby objects with attributes that require data type coercions.

Installation

gem i virtus

Basic Usage

require 'virtus'

class User
  include Virtus

  attribute :name,     String
  attribute :age,      Integer
  attribute :birthday, DateTime
end

# setting attributes in the constructor
user = User.new(:name => 'Piotr', :age => 28)

# attribute readers
user.name  # => "Piotr"

# hash of attributes
user.attributes  # => { :name => "Piotr" }

# automatic coercion
user.age = '28'
user.age  # => 28

user.birthday = 'November 18th, 1983'
user.birthday  # => #<DateTime: 1983-11-18T00:00:00+00:00 (4891313/2,0/1,2299161)>

Default values

require 'virtus'

class Page
  include Virtus

  attribute :title,      String
  attribute :slug,       String,  :default => lambda { |post, attribute| post.title.downcase.gsub(' ', '-') }
  attribute :view_count, Integer, :default => 0
end

page = Page.new(:title => 'Virtus Is Awesome')
page.slug # => 'virtus-is-awesome'
page.view_count # => 0

Coercions

Virtus comes with a builtin coercion library. It's super easy to add your own coercion classes. Take a look:

require 'virtus'
require 'digest/md5'

class MD5 < Virtus::Attribute::Object
 primitive       String
 coercion_method :to_md5
end

module Virtus
 class Coercion
   class String < Virtus::Coercion::Object
     def self.to_md5(value)
       Digest::MD5.hexdigest(value)
     end
   end
 end
end

class User
  include Virtus

  attribute :name,     String
  attribute :password, MD5
end

user = User.new(:name => 'Piotr', :password => 'foobar')
user.name     # => 'Piotr'
user.password # => '3858f62230ac3c915f300c664312c63f'

Custom Attributes

require 'virtus'
require 'json'

module MyApp
  module Attributes
    class JSON < Virtus::Attribute::Object
      primitive Hash

      def coerce(value)
        ::JSON.parse(value)
      end
    end
  end

  class User
    include Virtus

    attribute :info, Attributes::JSON
  end
end

user = MyApp::User.new

user.info = '{"email":"[email protected]"}'
user.info  # => {"email"=>"[email protected]"}

Contributors

Dan Kubb (dkubb)
Chris Corbyn (d11wtq)
Emmanuel Gomez (emmanuel)

Note on Patches/Pull Requests

Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so I don't break it in a future version unintentionally.
Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
Send me a pull request. Bonus points for topic branches.