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! 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").

Methods

*_change
*_changed?
*_previous_change
*_previously_changed?
*_previously_was
*_was
*_will_change!
attribute_changed?
attribute_previously_changed?
attribute_previously_was
attribute_was
changed
changed?
changed_attributes
changes
changes_applied
clear_*_change
clear_attribute_changes
clear_changes_information
previous_changes
restore_*!
restore_attributes

Included Modules

ActiveModel::AttributeMethods

Instance Public methods

*_change

This method is generated for each attribute.

Returns the old and the new value of the attribute.

person = Person.new
person.name = 'Nick'
person.name_change # => [nil, 'Nick']

🔎 See on GitHub

*_changed?

This method is generated for each attribute.

Returns true if the attribute has unsaved changes.

person = Person.new
person.name = 'Andrew'
person.name_changed? # => true

🔎 See on GitHub

*_previous_change

This method is generated for each attribute.

Returns the old and the new value of the attribute before the last save.

person = Person.new
person.name = 'Emmanuel'
person.save
person.name_previous_change # => [nil, 'Emmanuel']

🔎 See on GitHub

*_previously_changed?(**options)

This method is generated for each attribute.

Returns true if the attribute previously had unsaved changes.

person = Person.new
person.name = 'Britanny'
person.save
person.name_previously_changed? # => true
person.name_previously_changed?(from: nil, to: 'Britanny') # => true

🔎 See on GitHub

*_previously_was

This method is generated for each attribute.

Returns the old value of the attribute before the last save.

person = Person.new
person.name = 'Sage'
person.save
person.name_previously_was  # => nil

🔎 See on GitHub

*_was

This method is generated for each attribute.

Returns the old value of the attribute.

person = Person.new(name: 'Steph')
person.name = 'Stephanie'
person.name_change # => ['Steph', 'Stephanie']

🔎 See on GitHub

*_will_change!

This method is generated for each attribute.

If an attribute is modified in-place then make use of *_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 *_will_change! on Active Record models.

person = Person.new('Sandy')
person.name_will_change!
person.name_change # => ['Sandy', 'Sandy']

🔎 See on GitHub

attribute_changed?(attr_name, **options)

Dispatch target for *_changed attribute methods.

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 293
    def attribute_changed?(attr_name, **options)
      mutations_from_database.changed?(attr_name.to_s, **options)
    end

🔎 See on GitHub

attribute_previously_changed?(attr_name, **options)

Dispatch target for *_previously_changed attribute methods.

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 303
    def attribute_previously_changed?(attr_name, **options)
      mutations_before_last_save.changed?(attr_name.to_s, **options)
    end

🔎 See on GitHub

attribute_previously_was(attr_name)

Dispatch target for *_previously_was attribute methods.

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 308
    def attribute_previously_was(attr_name)
      mutations_before_last_save.original_value(attr_name.to_s)
    end

🔎 See on GitHub

attribute_was(attr_name)

Dispatch target for *_was attribute methods.

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 298
    def attribute_was(attr_name)
      mutations_from_database.original_value(attr_name.to_s)
    end

🔎 See on GitHub

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 288
    def changed
      mutations_from_database.changed_attribute_names
    end

🔎 See on GitHub

changed?()

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

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

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 279
    def changed?
      mutations_from_database.any_changes?
    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 336
    def changed_attributes
      mutations_from_database.changed_values
    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 346
    def changes
      mutations_from_database.changes
    end

🔎 See on GitHub

changes_applied()

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

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 265
    def changes_applied
      unless defined?(@attributes)
        mutations_from_database.finalize_changes
      end
      @mutations_before_last_save = mutations_from_database
      forget_attribute_assignments
      @mutations_from_database = nil
    end

🔎 See on GitHub

clear_*_change

This method is generated for each attribute.

Clears all dirty data of the attribute: current changes and previous changes.

person = Person.new(name: 'Chris')
person.name = 'Jason'
person.name_change # => ['Chris', 'Jason']
person.clear_name_change
person.name_change # => nil

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 241
      attribute_method_suffix "_previously_changed?", "_changed?", parameters: "**options"

🔎 See on GitHub

clear_attribute_changes(attr_names)

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 324
    def clear_attribute_changes(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 318
    def clear_changes_information
      @mutations_before_last_save = nil
      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 356
    def previous_changes
      mutations_before_last_save.changes
    end

🔎 See on GitHub

restore_*!

This method is generated for each attribute.

Restores the attribute to the old value.

person = Person.new
person.name = 'Amanda'
person.restore_name!
person.name # => nil

🔎 See on GitHub

restore_attributes(attr_names = changed)

Restore all previous data of the provided attributes.

📝 Source code

# File activemodel/lib/active_model/dirty.rb, line 313
    def restore_attributes(attr_names = changed)
      attr_names.each { |attr_name| restore_attribute!(attr_name) }
    end

🔎 See on GitHub