Active Model Dirty

Provides a way to track changes in your object in the same way as Active Record does.

The requirements for implementing ActiveModel::Dirty are:

• include ActiveModel::Dirty in your object.

• Call define_attribute_methods passing each method you want to track.

• Call *_will_change! before each change to the tracked attribute.

• Call changes_applied after the changes are persisted.

• Call clear_changes_information when you want to reset the changes information.

• Call restore_attributes when you want to restore previous data.

A minimal implementation could be:

class Person include ActiveModel::Dirty define_attribute_methods :name def initialize @name = nil end def name @name end def name=(val) name_will_change! unless val == @name @name = val end def save # do persistence work changes_applied end def reload! # get the values from the persistence layer clear_changes_information end def rollback! restore_attributes end end 

A newly instantiated Person object is unchanged:

person = Person.new person.changed? # => false 

Change the name:

person.name = 'Bob' person.changed? # => true person.name_changed? # => true person.name_changed?(from: nil, to: "Bob") # => true person.name_was # => nil person.name_change # => [nil, "Bob"] person.name = 'Bill' person.name_change # => [nil, "Bill"] 

Save the changes:

person.save person.changed? # => false person.name_changed? # => false 

Reset the changes:

person.previous_changes # => {"name" => [nil, "Bill"]} person.name_previously_changed? # => true person.name_previously_changed?(from: nil, to: "Bill") # => true person.name_previous_change # => [nil, "Bill"] person.name_previously_was # => nil person.reload! person.previous_changes # => {} 

Rollback the changes:

person.name = "Uncle Bob" person.rollback! person.name # => "Bill" person.name_changed? # => false 

Assigning the same value leaves the attribute unchanged:

person.name = 'Bill' person.name_changed? # => false person.name_change # => nil 

Which attributes have changed?

person.name = 'Bob' person.changed # => ["name"] person.changes # => {"name" => ["Bill", "Bob"]} 

If an attribute is modified in-place then make use of {*_will_change!}[rdoc-label:method-i-2A_will_change-21] to mark that the attribute is changing. Otherwise Active Model can’t track changes to in-place attributes. Note that Active Record can detect in-place modifications automatically. You do not need to call *_will_change! on Active Record models.

person.name_will_change! person.name_change # => ["Bill", "Bill"] person.name << 'y' person.name_change # => ["Bill", "Billy"] 

Methods can be invoked as name_changed? or by passing an argument to the generic method attribute_changed?("name").

activemodel/lib/active_model/dirty.rb