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

If you wish to also track previous changes on save or update, you need to add 

  @previously_changed = changes

inside of your save or update method.

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
      @previously_changed = changes
      @changed_attributes.clear
    end

  end

Examples:

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_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

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 << 'y'
  person.name_change    # => ['Bill', 'Billy']
Methods
C
P
Included Modules
Instance Public methods
changed()

List of attributes with unsaved changes. 

  person.changed # => []
  person.name = 'bob'
  person.changed # => ['name']

Source: show | on GitHub 

     # File activemodel/lib/active_model/dirty.rb, line 108
108:     def changed
109:       changed_attributes.keys
110:     end
changed?()

Returns true if any attribute have unsaved changes, false otherwise. 

  person.changed? # => false
  person.name = 'bob'
  person.changed? # => true

Source: show | on GitHub 

     # File activemodel/lib/active_model/dirty.rb, line 100
100:     def changed?
101:       changed_attributes.any?
102:     end
changed_attributes()

Map of change attr => original value.

Source: show | on GitHub 

     # File activemodel/lib/active_model/dirty.rb, line 130
130:     def changed_attributes
131:       @changed_attributes ||= {}
132:     end
changes()

Map of changed attrs => [original value, new value]. 

  person.changes # => {}
  person.name = 'bob'
  person.changes # => { 'name' => ['bill', 'bob'] }

Source: show | on GitHub 

     # File activemodel/lib/active_model/dirty.rb, line 116
116:     def changes
117:       HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
118:     end
previous_changes()

Map of attributes that were changed when the model was saved. 

  person.name # => 'bob'
  person.name = 'robert'
  person.save
  person.previous_changes # => {'name' => ['bob, 'robert']}

Source: show | on GitHub 

     # File activemodel/lib/active_model/dirty.rb, line 125
125:     def previous_changes
126:       @previously_changed
127:     end