1. ActiveModel
ActiveRecord’s useful stuff

2. Gem Spec
• Part of Rails gem package
• Own standalone gem:
• gem ‘activemodel’
• Dependencies:
• gem ‘activesupport’

3. ActiveModel Packages
• ActiveModel::AttributeMethods
• ActiveModel::Callbacks
• ActiveModel::Conversion
• ActiveModel::Dirty
• ActiveModel::Naming
• ActiveModel::Observer
• ActiveModel::Serialization
• ActiveModel::Translation
• ActiveModel::Validations

4. ActiveModel Packages
• ActiveModel::AttributeMethods
• ActiveModel::Callbacks
• ActiveModel::Conversion
• ActiveModel::Dirty
• ActiveModel::Naming
• ActiveModel::Observer
• ActiveModel::Serialization
• ActiveModel::Translation
• ActiveModel::Validations

5. Validations
• Most Rails validations originate from ActiveModel
• Including ActiveModel::Validations gives you
• #valid?
• #errors
• Class methods for validation API

6. Validations API
declarative
• validates_acceptance_of • validates_exclusion_of
• validates_confirmation_of • validates_length_of
• validates_each • validates_numericality_of
• validates_format_of • validates_presence_of
• validates_inclusion_of • validates_with

7. Validations API
short form
• validates :field_name, :validator => options

8. Validation API
• validates_each :field_name, &block
• validate :method_name
• validate &block
• validates_with ValidatorClass

9. Callbacks
• In ActiveRecord, this is how before_create,
after_create and around_create are made.
• Two different steps: register callbacks and
execute callbacks.

10. Observers
• Use observers to decouple logic from
models.
• Observers use convention to identify
targets: ModelObserver observes Model
unless explicitly overridden.

11. Serialization
• Allows for models to define how they
would like to be serialized in a variety of
formats (including XML and JSON).
• Important for creation of presenters that
get sent as JSON in RESTful API.

12. Dirty
• ActiveModel provides an API for detecting
whether an object is “dirty” or not
(changed).
• Could be useful for operations that may or
may not be idempotent and you need to
know which (e.g. marking a message as
read).

13. Questions?