Active Model

ActiveModelActiveRecord’s useful stuff

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

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

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

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

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

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

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

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

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.

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).

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Active Model

by Derek Hammer on Jan 25, 2012

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