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README.rdoc

Active Model – model interfaces for Rails

Active Model provides a known set of interfaces for usage in model classes. They allow for Action Pack helpers to interact with non-ActiveRecord models, for example. Active Model also helps building custom ORMs for use outside of the Rails framework.

Prior to Rails 3.0, if a plugin or gem developer wanted to have an object interact with Action Pack helpers, it was required to either copy chunks of code from Rails, or monkey patch entire helpers to make them handle objects that did not exactly conform to the Active Record interface. This would result in code duplication and fragile applications that broke on upgrades. Active Model solves this by defining an explicit API. You can read more about the API in ActiveModel::Lint::Tests.

Active Model provides a default module that implements the basic API required to integrate with Action Pack out of the box: +ActiveModel::Model+.

class Person
  include ActiveModel::Model

  attr_accessor :name, :age
  validates_presence_of :name
end

person = Person.new(:name => 'bob', :age => '18')
person.name # => 'bob'
person.age # => 18
person.valid? # => false

It includes model name introspections, conversions, translations and validations, resulting in a class suitable to be used with Action Pack. See +ActiveModel::Model+ for more examples.

Active Model also provides the following functionality to have ORM-like behavior out of the box:

  • Add attribute magic to objects

    class Person
      include ActiveModel::AttributeMethods
    
      attribute_method_prefix 'clear_'
      define_attribute_methods [:name, :age]
    
      attr_accessor :name, :age
    
      def clear_attribute(attr)
        send("#{attr}=", nil)
      end
    end
    
    person.clear_name
    person.clear_age

    Learn more

  • Callbacks for certain operations

    class Person
      extend ActiveModel::Callbacks
      define_model_callbacks :create
    
      def create
        run_callbacks :create do
          # Your create action methods here
        end
      end
    end

    This generates before_create, around_create and after_create class methods that wrap your create method.

    Learn more

  • Tracking value changes

    The ActiveModel::Dirty module allows for tracking attribute changes:

    person = Person.new
    person.name # => nil
    person.changed? # => false
    person.name = 'bob'
    person.changed? # => true
    person.changed # => ['name']
    person.changes # => { 'name' => [nil, 'bob'] }
    person.name = 'robert'
    person.save
    person.previous_changes # => {'name' => ['bob, 'robert']}

    Learn more

  • Adding errors interface to objects

    Exposing error messages allows objects to interact with Action Pack helpers seamlessly.

    class Person
    
      def initialize
        @errors = ActiveModel::Errors.new(self)
      end
    
      attr_accessor :name
      attr_reader   :errors
    
      def validate!
        errors.add(:name, "can not be nil") if name.nil?
      end
    
      def self.human_attribute_name(attr, options = {})
        "Name"
      end
    end
    
    person.errors.full_messages
    # => ["Name can not be nil"]
    
    person.errors.full_messages
    # => ["Name can not be nil"]

    Learn more

  • Model name introspection

    class NamedPerson
      extend ActiveModel::Naming
    end
    
    NamedPerson.model_name        # => "NamedPerson"
    NamedPerson.model_name.human  # => "Named person"

    Learn more

  • Observer support

    ActiveModel::Observers allows your object to implement the Observer pattern in a Rails App and take advantage of all the standard observer functions.

    Learn more

  • Making objects serializable

    ActiveModel::Serialization provides a standard interface for your object to provide to_json or to_xml serialization.

    s = SerialPerson.new
    s.serializable_hash   # => {"name"=>nil}
    s.to_json             # => "{\"name\":null}"
    s.to_xml              # => "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<serial-person...

    Learn more

  • Internationalization (i18n) support

    class Person
      extend ActiveModel::Translation
    end
    
    Person.human_attribute_name('my_attribute')
    # => "My attribute"

    Learn more

  • Validation support

    class Person
      include ActiveModel::Validations
    
      attr_accessor :first_name, :last_name
    
      validates_each :first_name, :last_name do |record, attr, value|
        record.errors.add attr, 'starts with z.' if value.to_s[0] == ?z
      end
    end
    
    person = Person.new
    person.first_name = 'zoolander'
    person.valid?  # => false

    Learn more

  • Custom validators

    class ValidatorPerson
      include ActiveModel::Validations
      validates_with HasNameValidator
      attr_accessor :name
    end
    
    class HasNameValidator < ActiveModel::Validator
      def validate(record)
        record.errors[:name] = "must exist" if record.name.blank?
      end
    end
    
    p = ValidatorPerson.new
    p.valid?                  # =>  false
    p.errors.full_messages    # => ["Name must exist"]
    p.name = "Bob"
    p.valid?                  # =>  true

    Learn more

Download and installation

The latest version of Active Model can be installed with RubyGems:

% [sudo] gem install activemodel

Source code can be downloaded as part of the Rails project on GitHub

License

Active Model is released under the MIT license:

Support

API documentation is at

Bug reports and feature requests can be filed with the rest for the Ruby on Rails project here:

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