ActiveModel::Dirty

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 attr_name_will_change! before each change to the tracked attribute.

• Call changes_applied after the changes are persisted.

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

A minimal implementation could be:

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 def reload! reset_changes end end 

A newly instantiated object is unchanged:

person = Person.find_by(name: 'Uncle Bob') person.changed? # => false 

Change the name:

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

Save the changes:

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

Reset the changes:

person.previous_changes # => {"name" => ["Uncle Bob", "Bill"]} person.reload! person.previous_changes # => {} 

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 [attribute_name]_will_change! to mark that the attribute is changing. Otherwise ActiveModel can’t track changes to in-place attributes.

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

activemodel/lib/active_model/dirty.rb