module 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 *_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").

Public Instance 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']

# File activemodel/lib/active_model/dirty.rb, line 155

*_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

# File activemodel/lib/active_model/dirty.rb, line 144

*_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']

# File activemodel/lib/active_model/dirty.rb, line 193

*_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

# File activemodel/lib/active_model/dirty.rb, line 129

*_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

# File activemodel/lib/active_model/dirty.rb, line 205

*_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_was # => 'Steph'

# File activemodel/lib/active_model/dirty.rb, line 182

*_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']

# File activemodel/lib/active_model/dirty.rb, line 166

attribute_changed? (attr_name, **options)

Dispatch target for *_changed? attribute methods.

# 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

attribute_previously_changed? (attr_name, **options)

Dispatch target for *_previously_changed? attribute methods.

# 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

attribute_previously_was (attr_name)

Dispatch target for *_previously_was attribute methods.

# 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

attribute_was (attr_name)

Dispatch target for *_was attribute methods.

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

changed ()

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

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

# File activemodel/lib/active_model/dirty.rb, line 288
def changed
  mutations_from_database.changed_attribute_names
end

changed? ()

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

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

# File activemodel/lib/active_model/dirty.rb, line 279
def changed?
  mutations_from_database.any_changes?
end

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"}

# File activemodel/lib/active_model/dirty.rb, line 336
def changed_attributes
  mutations_from_database.changed_values
end

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"] }

# File activemodel/lib/active_model/dirty.rb, line 346
def changes
  mutations_from_database.changes
end

changes_applied ()

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

# 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

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

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

clear_attribute_changes (attr_names)

# 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

clear_changes_information ()

Clears all dirty data: current changes and previous changes.

# 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

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"]}

# File activemodel/lib/active_model/dirty.rb, line 356
def previous_changes
  mutations_before_last_save.changes
end

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

# File activemodel/lib/active_model/dirty.rb, line 217

restore_attributes (attr_names = changed)

Restore all previous data of the provided attributes.

# 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