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::Dirtyin your object

  • Call define_attribute_methodspassing 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']
# File activemodel/lib/active_model/dirty.rb, line 108
def changed
  changed_attributes.keys
end
changed?()

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

person.changed? # => false
person.name = 'bob'
person.changed? # => true
# File activemodel/lib/active_model/dirty.rb, line 100
def changed?
  changed_attributes.any?
end
changed_attributes()

Map of change attr => original value.

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

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

person.changes # => {}
person.name = 'bob'
person.changes # => { 'name' => ['bill', 'bob'] }
# File activemodel/lib/active_model/dirty.rb, line 116
def changes
  HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
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']}
# File activemodel/lib/active_model/dirty.rb, line 125
def previous_changes
  @previously_changed
end