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).