= 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-Active Record models,
for example. Active Model also helps with building custom ORMs for use outside of
the Rails framework.
You can read more about Active Model in the {Active Model Basics}[https://edgeguides.rubyonrails.org/active_model_basics.html] guide.
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 <tt>ActiveModel::Lint::Tests</tt>.
Active Model provides a default module that implements the basic API required
to integrate with Action Pack out of the box: <tt>ActiveModel::API</tt>.
class Person
include ActiveModel::API
attr_accessor :name, :age
validates_presence_of :name
end
person = Person.new(name: 'bob', age: '18')
person.name # => 'bob'
person.age # => '18'
person.valid? # => true
It includes model name introspections, conversions, translations and
validations, resulting in a class suitable to be used with Action Pack.
See <tt>ActiveModel::API</tt> 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 = Person.new
person.clear_name
person.clear_age
{Learn more}[link:classes/ActiveModel/AttributeMethods.html]
* 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}[link:classes/ActiveModel/Callbacks.html]
* Tracking value changes
class Person
include ActiveModel::Dirty
define_attribute_methods :name
def name
@name
end
def name=(val)
name_will_change! unless val == @name
@name = val
end
def save
# do persistence work
changes_applied
end
end
person = Person.new
person.name # => nil
person.changed? # => false
person.name = 'bob'
person.changed? # => true
person.changed # => ['name']
person.changes # => { 'name' => [nil, 'bob'] }
person.save
person.name = 'robert'
person.save
person.previous_changes # => {'name' => ['bob, 'robert']}
{Learn more}[link:classes/ActiveModel/Dirty.html]
* 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, "cannot be nil") if name.nil?
end
def self.human_attribute_name(attr, options = {})
"Name"
end
end
person = Person.new
person.name = nil
person.validate!
person.errors.full_messages
# => ["Name cannot be nil"]
{Learn more}[link:classes/ActiveModel/Errors.html]
* Model name introspection
class NamedPerson
extend ActiveModel::Naming
end
NamedPerson.model_name.name # => "NamedPerson"
NamedPerson.model_name.human # => "Named person"
{Learn more}[link:classes/ActiveModel/Naming.html]
* Making objects serializable
<tt>ActiveModel::Serialization</tt> provides a standard interface for your object
to provide +to_json+ serialization.
class SerialPerson
include ActiveModel::Serialization
attr_accessor :name
def attributes
{'name' => name}
end
end
s = SerialPerson.new
s.serializable_hash # => {"name"=>nil}
class SerialPerson
include ActiveModel::Serializers::JSON
end
s = SerialPerson.new
s.to_json # => "{\"name\":null}"
{Learn more}[link:classes/ActiveModel/Serialization.html]
* Internationalization (i18n) support
class Person
extend ActiveModel::Translation
end
Person.human_attribute_name('my_attribute')
# => "My attribute"
{Learn more}[link:classes/ActiveModel/Translation.html]
* 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.start_with?("z")
end
end
person = Person.new
person.first_name = 'zoolander'
person.valid? # => false
{Learn more}[link:classes/ActiveModel/Validations.html]
* Custom validators
class HasNameValidator < ActiveModel::Validator
def validate(record)
record.errors.add(:name, "must exist") if record.name.blank?
end
end
class ValidatorPerson
include ActiveModel::Validations
validates_with HasNameValidator
attr_accessor :name
end
p = ValidatorPerson.new
p.valid? # => false
p.errors.full_messages # => ["Name must exist"]
p.name = "Bob"
p.valid? # => true
{Learn more}[link:classes/ActiveModel/Validator.html]
== Download and installation
The latest version of Active Model can be installed with RubyGems:
$ gem install activemodel
Source code can be downloaded as part of the Rails project on GitHub
* https://github.com/rails/rails/tree/main/activemodel
== License
Active Model is released under the MIT license:
* https://opensource.org/licenses/MIT
== Support
API documentation is at:
* https://api.rubyonrails.org
Bug reports for the Ruby on Rails project can be filed here:
* https://github.com/rails/rails/issues
Feature requests should be discussed on the rails-core mailing list here:
* https://discuss.rubyonrails.org/c/rubyonrails-core
0fb166e81c