ShallowAttributes

Simple and lightweight Virtus analog without any dependencies. Documentation.

Motivation

There are already a lot of good and flexible gems which solve a similar problem, allowing attributes to be defined with their types, for example: virtus, fast_attributes or attrio. However, the disadvantage of these gems is performance or API. So, the goal of ShallowAttributes is to provide a simple solution which is similar to the Virtus API, simple, fast, understandable and extendable.

This is the performance benchmark of ShallowAttributes compared to Virtus gems.
Default ruby struct, dry-struct, virtus and ShallowAttributes ips and memory benchmarks

Installation

Add this line to your application's Gemfile:

gem 'shallow_attributes'

And then execute:

$ bundle

Or install it yourself as:

$ gem install shallow_attributes

Examples

Using ShallowAttributes with Classes
Default Values
Mandatory Attributes
Embedded Value
Custom Coercions
Collection Member Coercions
Note about Member Coercions
Overriding setters
ActiveModel compatibility
Dry-types

Using ShallowAttributes with Classes

You can create classes extended with Virtus and define attributes:

class User
  include ShallowAttributes

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

class SuperUser < User
  include ShallowAttributes

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

user = User.new(name: 'Anton', age: 31)
user.name       # => "Anton"

user.age = '31' # => 31
user.age = nil  # => nil
user.age.class  # => Fixnum

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

user.attributes # => { name: "Anton", age: 31, birthday: nil }

# mass-assignment
user.attributes = { name: 'Jane', age: 21 }
user.name       # => "Jane"
user.age        # => 21

super_user = SuperUser.new
user.age = nil  # => 0

ShallowAttributes doesn't make any assumptions about base classes. There is no need to define default attributes, or even mix ShallowAttributes into the base class:

require 'active_model'

class Form
  extend ActiveModel::Naming
  extend ActiveModel::Translation
  include ActiveModel::Conversion
  include ShallowAttributes

  def persisted?
    false
  end
end

class SearchForm < Form
  attribute :name, String
end

form = SearchForm.new(name: 'Anton')
form.name # => "Anton"

Default Values

class Page
  include ShallowAttributes

  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

  private

  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                    # => 0

Mandatory attributes

You can provide present: true option for any attribute that will prevent class from initialization if this attribute was not provided:

class CreditCard
  include ShallowAttributes
  attribute :number, Integer, present: true
  attribute :owner, String, present: true
end

card = CreditCard.new(number: 1239342)
# => ShallowAttributes::MissingAttributeError: Mandatory attribute "owner" was not provided

Embedded Value

class City
  include ShallowAttributes

  attribute :name, String
  attribute :size, Integer, default: 9000
end

class Address
  include ShallowAttributes

  attribute :street,  String
  attribute :zipcode, String, default: '111111'
  attribute :city,    City
end

class User
  include ShallowAttributes

  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"

Custom Coercions

require 'json'

class Json
  def coerce(value, options = {})
    value.is_a?(::Hash) ? value : JSON.parse(value)
  end
end

class User
  include ShallowAttributes

  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
  def coerce(value, options = {})
    value.to_s.upcase
  end
end

class User
  include ShallowAttributes

  attribute :scream, NoisyString
end

user = User.new(scream: 'hello world!')
user.scream # => "HELLO WORLD!"

Collection Member Coercions

# Support "primitive" classes
class Book
  include ShallowAttributes

  attribute :page_numbers, Array, of: Integer
end

book = Book.new(:page_numbers => %w[1 2 3])
book.page_numbers # => [1, 2, 3]

# Support EmbeddedValues, too!
class Address
  include ShallowAttributes

  attribute :address,     String
  attribute :locality,    String
  attribute :region,      String
  attribute :postal_code, String
end

class PhoneNumber
  include ShallowAttributes

  attribute :number, String
end

class User
  include ShallowAttributes

  attribute :phone_numbers, Array, of: PhoneNumber
  attribute :addresses,     Array, of: 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     # => [#<Address:0x007fdb2d3be448 @address="1234 Any St.", @locality="Anytown", @region="DC", @postal_code="21234">]

user.attributes
# => {
# =>   :phone_numbers => [
# =>     { :number => '212-555-1212' },
# =>     { :number => '919-444-3265' }
# =>   ],
# =>   :addresses => [
# =>     {
# =>       :address => '1234 Any St.',
# =>       :locality => 'Anytown',
# =>       :region => "DC",
# =>       :postal_code => "21234"
# =>     }
# =>   ]
# => }

IMPORTANT note about member coercions

ShallowAttributes 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 ShallowAttributes
  attribute :title, String
end

class Library
  include ShallowAttributes
  attribute :books, Array, of: Book
end

library = Library.new

# This will coerce Hash to a Book instance
library.books = [ { :title => 'Introduction' } ]

# This WILL NOT COERCE the value because you mutate the books array with Array#<<
library.books << { :title => 'Another Introduction' }

Overriding setters

class User
  include ShallowAttributes

  attribute :name, String

  alias_method :_name=, :name=
  def name=(new_name)
    custom_name = nil
    if new_name == "Godzilla"
      custom_name = "Can't tell"
    end

    self._name = custom_name || new_name
  end
end

user = User.new(name: "Frank")
user.name # => 'Frank'

user = User.new(name: "Godzilla")
user.name # => 'Can't tell'

ActiveModel compatibility

ShallowAttributes is fully compatible with ActiveModel.

Form object

require 'active_model'

class SearchForm
  extend ActiveModel::Naming
  extend ActiveModel::Translation
  include ActiveModel::Conversion
  include ShallowAttributes

  attribute :name, String
  attribute :service_ids, Array, of: Integer
  attribute :archived, 'Boolean', default: false

  def persisted?
    false
  end

  def results
    # ...
  end
end

class SearchesController < ApplicationController
  def index
    search_params = params.require(:search_form).permit(...)
    @search_form = SearchForm.new(search_params)
  end
end

<h1>Search</h1>
<%= form_for @search_form do |f| %>
  <%= f.text_field :name %>
  <%= f.collection_check_boxes :service_ids, Service.all, :id, :name %>
  <%= f.select :archived, [['Archived', true], ['Not Archived', false]] %>
<% end %>

Validations

require 'active_model'

class Children
  include ShallowAttributes
  include ActiveModel::Validations

  attribute :scream, String
  validates :scream, presence: true
end

user = User.new(scream: '')
user.valid? # => false
user.scream = 'hello world!'
user.valid? # => true

Dry-types

You can use dry-types objects as a type for your attribute:

module Types
  include Dry::Types.module
end

class User
  include ShallowAttributes

  attribute :name, Types::Coercible::String
  attribute :age, Types::Coercible::Int
  attribute :birthday, DateTime
end

user = User.new(name: nil, age: 0)
user.name # => ''
user.age # => 0

Ruby version support

ShallowAttributes is known to work correctly with the following rubies:

2.0
2.1
2.2
2.3
2.4
jruby-head

Also we run rbx-2 buld too.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/davydovanton/shallow_attributes. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.