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 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_previous_change     # => [nil, "Bill"]
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 [attribute_name]_will_change! 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 [attribute_name]_will_change! on Active Record models.

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

Methods

Included Modules

Instance Public methods

changed()

Returns an array with the name of the attributes with unsaved changes.

person.changed # => []
person.name = 'bob'
person.changed # => ["name"]
📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 170
    def changed
      changed_attributes.keys
    end
🔎 See on GitHub

changed?()

Returns true if any of the attributes have unsaved changes, false otherwise.

person.changed? # => false
person.name = 'bob'
person.changed? # => true
📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 161
    def changed?
      changed_attributes.present?
    end
🔎 See on GitHub

changed_attributes()

Returns a hash of the attributes with unsaved changes indicating their original values like attr => original value.

person.name # => "bob"
person.name = 'robert'
person.changed_attributes # => {"name" => "bob"}
📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 218
    def changed_attributes
      # This should only be set by methods which will call changed_attributes
      # multiple times when it is known that the computed value cannot change.
      if defined?(@cached_changed_attributes)
        @cached_changed_attributes
      else
        attributes_changed_by_setter.reverse_merge(mutations_from_database.changed_values).freeze
      end
    end
🔎 See on GitHub

changes()

Returns a hash of changed attributes indicating their original and new values like attr => [original value, new value].

person.changes # => {}
person.name = 'bob'
person.changes # => { "name" => ["bill", "bob"] }
📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 234
    def changes
      cache_changed_attributes do
        ActiveSupport::HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
      end
    end
🔎 See on GitHub

changes_applied()

Clears dirty data and moves changes to previously_changed and mutations_from_database to mutations_before_last_save respectively.

📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 146
    def changes_applied
      unless defined?(@attributes)
        @previously_changed = changes
      end
      @mutations_before_last_save = mutations_from_database
      @attributes_changed_by_setter = ActiveSupport::HashWithIndifferentAccess.new
      forget_attribute_assignments
      @mutations_from_database = nil
    end
🔎 See on GitHub

clear_attribute_changes(attr_names)

📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 205
    def clear_attribute_changes(attr_names)
      attributes_changed_by_setter.except!(*attr_names)
      attr_names.each do |attr_name|
        clear_attribute_change(attr_name)
      end
    end
🔎 See on GitHub

clear_changes_information()

Clears all dirty data: current changes and previous changes.

📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 197
    def clear_changes_information
      @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
      @mutations_before_last_save = nil
      @attributes_changed_by_setter = ActiveSupport::HashWithIndifferentAccess.new
      forget_attribute_assignments
      @mutations_from_database = nil
    end
🔎 See on GitHub

previous_changes()

Returns a hash of attributes that were changed before the model was saved.

person.name # => "bob"
person.name = 'robert'
person.save
person.previous_changes # => {"name" => ["bob", "robert"]}
📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 246
    def previous_changes
      @previously_changed ||= ActiveSupport::HashWithIndifferentAccess.new
      @previously_changed.merge(mutations_before_last_save.changes)
    end
🔎 See on GitHub

restore_attributes(attributes = changed)

Restore all previous data of the provided attributes.

📝 Source code
# File activemodel/lib/active_model/dirty.rb, line 192
    def restore_attributes(attributes = changed)
      attributes.each { |attr| restore_attribute! attr }
    end
🔎 See on GitHub