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.
$ gem install virtus
or in your Gemfile
gem 'virtus'You can create classes extended with virtus and define attributes:
class User
include Virtus
attribute :name, String
attribute :age, Integer
attribute :birthday, DateTime
end
user = User.new(:name => 'Piotr', :age => 28)
user.attributes # => { :name => "Piotr", :age => 28 }
user.name # => "Piotr"
user.age = '28' # => 28
user.age.class # => Fixnum
user.birthday = 'November 18th, 1983' # => #<DateTime: 1983-11-18T00:00:00+00:00 (4891313/2,0/1,2299161)>
# mass-assignment
user.attributes = { :name => 'Jane', :age => 21 }
user.name # => "Jane"
user.age # => 21You can create modules extended with virtus and define attributes for later inclusion in your classes:
module Name
include Virtus
attribute :name, String
end
module Age
include Virtus
attribute :age, Integer
end
class User
include Name, Age
end
user = User.new(:name => 'John', :age => '30')It's also possible to dynamically extend an object with Virtus:
class User
# nothing here
end
user = User.new
user.extend(Virtus)
user.attribute :name, String
user.name = 'John'
user.name # => 'John'class Page
include Virtus
attribute :title, String
# default from a singleton value (integer in this case)
attribute :views, Integer, :default => 0
# default from a singleton value (boolean in this case)
attribute :published, Boolean, :default => false
# default from a callable object (proc in this case)
attribute :slug, String, :default => lambda { |page, attribute| page.title.downcase.gsub(' ', '-') }
# default from a method name as symbol
attribute :editor_title, String, :default => :default_editor_title
def default_editor_title
published? ? title : "UNPUBLISHED: #{title}"
end
end
page = Page.new(:title => 'Virtus README')
page.slug # => 'virtus-readme'
page.views # => 0
page.published # => false
page.editor_title # => "UNPUBLISHED: Virtus README"class City
include Virtus
attribute :name, String
end
class Address
include Virtus
attribute :street, String
attribute :zipcode, String
attribute :city, City
end
class User
include Virtus
attribute :name, String
attribute :address, Address
end
user = User.new(:address => {
:street => 'Street 1/2', :zipcode => '12345', :city => { :name => 'NYC' } })
user.address.street # => "Street 1/2"
user.address.city.name # => "NYC"# Support "primitive" classes
class Book
include Virtus
attribute :page_numbers, Array[Integer]
end
book = Book.new(:page_numbers => %w[1 2 3])
book.page_numbers # => [1, 2, 3]
# Support EmbeddedValues, too!
class Address
include Virtus
attribute :address, String
attribute :locality, String
attribute :region, String
attribute :postal_code, String
end
class PhoneNumber
include Virtus
attribute :number, String
end
class User
include Virtus
attribute :phone_numbers, Array[PhoneNumber]
attribute :addresses, Set[Address]
end
user = User.new(
:phone_numbers => [
{ :number => '212-555-1212' },
{ :number => '919-444-3265' } ],
:addresses => [
{ :address => '1234 Any St.', :locality => 'Anytown', :region => "DC", :postal_code => "21234" } ])
user.phone_numbers # => [#<PhoneNumber:0x007fdb2d3bef88 @number="212-555-1212">, #<PhoneNumber:0x007fdb2d3beb00 @number="919-444-3265">]
user.addresses # => #<Set: {#<Address:0x007fdb2d3be448 @address="1234 Any St.", @locality="Anytown", @region="DC", @postal_code="21234">}>class Package
include Virtus
attribute :dimensions, Hash[Symbol => Float]
end
package = Package.new(:dimensions => { 'width' => "2.2", :height => 2, "length" => 4.5 })
package.dimensions # => { :width => 2.2, :height => 2.0, :length => 4.5 }Virtus performs coercions only when a value is being assigned. If you mutate the value later on using its own interfaces then coercion won't be triggered.
Here's an example:
class Book
include Virtus
attribute :title, String
end
class Library
include Virtus
attribute :books, Array[Book]
end
library = Library.new
# This will coerce Hash to a Book instance
library.books = [ { :title => 'Introduction to Virtus' } ]
# This WILL NOT COERCE the value because you mutate the books array with Array#<<
library.books << { :title => 'Another Introduction to Virtus' }A suggested solution to this problem would be to introduce your own class instead of using Array and implement mutation methods that perform coercions. For example:
class Book
include Virtus
attribute :title, String
end
class BookCollection < Array
def <<(book)
if book.kind_of?(Hash)
super(Book.new(book))
else
super
end
end
end
class Library
include Virtus
attribute :books, BookCollection[Book]
end
library = Library.new
library.books << { :title => 'Another Introduction to Virtus' }class GeoLocation
include Virtus::ValueObject
attribute :latitude, Float
attribute :longitude, Float
end
class Venue
include Virtus
attribute :name, String
attribute :location, GeoLocation
end
venue = Venue.new(
:name => 'Pub',
:location => { :latitude => 37.160317, :longitude => -98.437500 })
venue.location.latitude # => 37.160317
venue.location.longitude # => -98.4375
# Supports object's equality
venue_other = Venue.new(
:name => 'Other Pub',
:location => { :latitude => 37.160317, :longitude => -98.437500 })
venue.location === venue_other.location # => trueVirtus comes with a builtin coercion library. It's super easy to add your own coercion classes. Take a look:
require 'digest/md5'
# Our new attribute type
class MD5 < Virtus::Attribute::Object
primitive String
coercion_method :to_md5
end
# Defining the Coercion method
module Virtus
class Coercion
class String < Virtus::Coercion::Object
def self.to_md5(value)
Digest::MD5.hexdigest value
end
end
end
end
# And now the user!
class User
include Virtus
attribute :name, String
attribute :password, MD5
end
user = User.new(:name => 'Piotr', :password => 'foobar')
user.name # => 'Piotr'
user.password # => '3858f62230ac3c915f300c664312c63f'require 'json'
module MyApp
# Defining the custom attribute(s)
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":"john@domain.com"}' # => {"email"=>"john@domain.com"}
user.info.class # => Hash- Dan Kubb (dkubb)
- Chris Corbyn (d11wtq)
- Emmanuel Gomez (emmanuel)
- Fabio Rehm (fgrehm)
- Ryan Closner (rclosner)
- Markus Schirp (mbj)
- Yves Senn (senny)
- 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 or version (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.
Copyright (c) 2011-2012 Piotr Solnica
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
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