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 use case 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.model
attribute :name, String
attribute :age, Integer
attribute :birthday, DateTime
end
user = User.new(:name => 'Piotr', :age => 29)
user.attributes # => { :name => "Piotr", :age => 29 }
user.name # => "Piotr"
user.age = '29' # => 29
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 # => 21# include attribute DSL + constructor + mass-assignment
class User
include Virtus.model
attribute :name, String
end
user = User.new(:name => 'Piotr')
user.attributes = { :name => 'John' }
user.attributes
# => {:name => 'John'}
# include attribute DSL + constructor
class User
include Virtus.model(:mass_assignment => false)
attribute :name, String
end
User.new(:name => 'Piotr')
# include just the attribute DSL
class User
include Virtus.model(:constructor => false, :mass_assignment => false)
attribute :name, String
end
user = User.new
user.name = 'Piotr'You can create modules extended with Virtus and define attributes for later inclusion in your classes:
module Name
include Virtus.module
attribute :name, String
end
module Age
include Virtus.module(:coerce => false)
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.model)
user.attribute :name, String
user.name = 'John'
user.name # => 'John'class Page
include Virtus.model
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"
page.views = 10
page.views # => 10
page.reset_attribute(:views) # => 0
page.views # => 0class City
include Virtus.model
attribute :name, String
end
class Address
include Virtus.model
attribute :street, String
attribute :zipcode, String
attribute :city, City
end
class User
include Virtus.model
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.model
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.model
attribute :address, String
attribute :locality, String
attribute :region, String
attribute :postal_code, String
end
class PhoneNumber
include Virtus.model
attribute :number, String
end
class User
include Virtus.model
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.model
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 }Be aware that some libraries may do a terrible thing and define a global Boolean constant which breaks virtus' constant type lookup, if you see issues with the boolean type you can workaround it like that:
class User
include Virtus.model
attribute :admin, Axiom::Types::Boolean
endThis will be improved in Virtus 2.0.
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.model
attribute :title, String
end
class Library
include Virtus.model
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.model
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.model
attribute :books, BookCollection[Book]
end
library = Library.new
library.books << { :title => 'Another Introduction to Virtus' }class GeoLocation
include Virtus.value_object
values do
attribute :latitude, Float
attribute :longitude, Float
end
end
class Venue
include Virtus.value_object
values do
attribute :name, String
attribute :location, GeoLocation
end
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 # => truerequire 'json'
class Json < Virtus::Attribute
def coerce(value)
value.is_a?(::Hash) ? value : JSON.parse(value)
end
end
class User
include Virtus.model
attribute :info, Json, default: {}
end
user = User.new
user.info = '{"email":"john@domain.com"}' # => {"email"=>"john@domain.com"}
user.info.class # => Hash
# With a custom attribute encapsulating coercion-specific configuration
class NoisyString < Virtus::Attribute
def coerce(value)
value.to_s.upcase
end
end
class User
include Virtus.model
attribute :scream, NoisyString
end
user = User.new(:scream => 'hello world!')
user.scream # => "HELLO WORLD!"class User
include Virtus.model
attribute :unique_id, String, :writer => :private
def set_unique_id(id)
self.unique_id = id
end
end
user = User.new(:unique_id => '1234-1234')
user.unique_id # => nil
user.unique_id = '1234-1234' # => NoMethodError: private method `unique_id='
user.set_unique_id('1234-1234')
user.unique_id # => '1234-1234'class User
include Virtus.model
attribute :name, String
def name=(new_name)
custom_name = nil
if new_name == "Godzilla"
custom_name = "Can't tell"
end
super custom_name || new_name
end
end
user = User.new(name: "Frank")
user.name # => 'Frank'
user = User.new(name: "Godzilla")
user.name # => 'Can't tell'By default Virtus returns the input value even when it couldn't coerce it to the expected type. If you want to catch such cases in a noisy way you can use the strict mode in which Virtus raises an exception when it failed to coerce an input value.
class User
include Virtus.model(:strict => true)
attribute :admin, Boolean
end
# this will raise an error
User.new :admin => "can't really say if true or false"You can also build Virtus modules that contain their own configuration.
YupNopeBooleans = Virtus.model { |mod|
mod.coerce = true
mod.coercer.config.string.boolean_map = { 'nope' => false, 'yup' => true }
}
class User
include YupNopeBooleans
attribute :name, String
attribute :admin, Boolean
end
# Or just include the module straight away ...
class User
include Virtus.model(:coerce => false)
attribute :name, String
attribute :admin, Boolean
endIf a type references another type which happens to not be available yet you need to use lazy-finalization of attributes and finalize virtus manually after all types have been already loaded:
# in blog.rb
class Blog
include Virtus.model(:finalize => false)
attribute :posts, Array['Post']
end
# in post.rb
class Post
include Virtus.model(:finalize => false)
attribute :blog, 'Blog'
end
# after loading both files just do:
Virtus.finalize
# constants will be resolved:
Blog.attribute_set[:posts].member_type.primitive # => Post
Post.attribute_set[:blog].type.primitive # => BlogVirtus is known to work correctly with the following rubies:
- 1.9.3
- 2.0.0
- 2.1.2
- jruby
- (probably) rbx
- 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.