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:

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"]

Public Instance Methods

changed() click to toggle source

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

person.changed # => []
person.name = 'bob'
person.changed # => ["name"]
# File lib/active_model/dirty.rb, line 167
def changed
  changed_attributes.keys
end
changed?() click to toggle source

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

person.changed? # => false
person.name = 'bob'
person.changed? # => true
# File lib/active_model/dirty.rb, line 158
def changed?
  changed_attributes.present?
end
changed_attributes() click to toggle source

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 lib/active_model/dirty.rb, line 215
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
changes() click to toggle source

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 lib/active_model/dirty.rb, line 231
def changes
  cache_changed_attributes do
    ActiveSupport::HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
  end
end
clear_attribute_changes(attr_names) click to toggle source
# File lib/active_model/dirty.rb, line 202
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
clear_changes_information() click to toggle source

Clears all dirty data: current changes and previous changes.

# File lib/active_model/dirty.rb, line 194
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
previous_changes() click to toggle source

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 lib/active_model/dirty.rb, line 243
def previous_changes
  @previously_changed ||= ActiveSupport::HashWithIndifferentAccess.new
  @previously_changed.merge(mutations_before_last_save.changes)
end
restore_attributes(attributes = changed) click to toggle source

Restore all previous data of the provided attributes.

# File lib/active_model/dirty.rb, line 189
def restore_attributes(attributes = changed)
  attributes.each { |attr| restore_attribute! attr }
end

Private Instance Methods

attribute_change(attr) click to toggle source

Handles *_change for method_missing.

# File lib/active_model/dirty.rb, line 300
def attribute_change(attr)
  [changed_attributes[attr], _read_attribute(attr)] if attribute_changed?(attr)
end
attribute_changed_by_setter?(attr_name)
Alias for: changes_include?
attribute_previous_change(attr) click to toggle source

Handles *_previous_change for method_missing.

# File lib/active_model/dirty.rb, line 305
def attribute_previous_change(attr)
  previous_changes[attr] if attribute_previously_changed?(attr)
end
attribute_will_change!(attr) click to toggle source

Handles *_will_change! for method_missing.

# File lib/active_model/dirty.rb, line 310
def attribute_will_change!(attr)
  unless attribute_changed?(attr)
    begin
      value = _read_attribute(attr)
      value = value.duplicable? ? value.clone : value
    rescue TypeError, NoMethodError
    end

    set_attribute_was(attr, value)
  end
  mutations_from_database.force_change(attr)
end
attributes_changed_by_setter() click to toggle source
# File lib/active_model/dirty.rb, line 331
def attributes_changed_by_setter
  @attributes_changed_by_setter ||= ActiveSupport::HashWithIndifferentAccess.new
end
cache_changed_attributes() { || ... } click to toggle source
# File lib/active_model/dirty.rb, line 276
def cache_changed_attributes
  @cached_changed_attributes = changed_attributes
  yield
ensure
  clear_changed_attributes_cache
end
changes_include?(attr_name) click to toggle source

Returns true if attr_name is changed, false otherwise.

# File lib/active_model/dirty.rb, line 288
def changes_include?(attr_name)
  attributes_changed_by_setter.include?(attr_name) || mutations_from_database.changed?(attr_name)
end
Also aliased as: attribute_changed_by_setter?
clear_attribute_change(attr_name) click to toggle source
# File lib/active_model/dirty.rb, line 253
def clear_attribute_change(attr_name)
  mutations_from_database.forget_change(attr_name)
end
clear_changed_attributes_cache() click to toggle source
# File lib/active_model/dirty.rb, line 283
def clear_changed_attributes_cache
  remove_instance_variable(:@cached_changed_attributes) if defined?(@cached_changed_attributes)
end
forget_attribute_assignments() click to toggle source
# File lib/active_model/dirty.rb, line 268
def forget_attribute_assignments
  @attributes = @attributes.map(&:forgetting_assignment) if defined?(@attributes)
end
mutations_before_last_save() click to toggle source
# File lib/active_model/dirty.rb, line 272
def mutations_before_last_save
  @mutations_before_last_save ||= ActiveModel::NullMutationTracker.instance
end
mutations_from_database() click to toggle source
# File lib/active_model/dirty.rb, line 257
def mutations_from_database
  unless defined?(@mutations_from_database)
    @mutations_from_database = nil
  end
  @mutations_from_database ||= if defined?(@attributes)
    ActiveModel::AttributeMutationTracker.new(@attributes)
  else
    NullMutationTracker.instance
  end
end
previous_changes_include?(attr_name) click to toggle source

Returns true if attr_name were changed before the model was saved, false otherwise.

# File lib/active_model/dirty.rb, line 295
def previous_changes_include?(attr_name)
  previous_changes.include?(attr_name)
end
restore_attribute!(attr) click to toggle source

Handles restore_*! for method_missing.

# File lib/active_model/dirty.rb, line 324
def restore_attribute!(attr)
  if attribute_changed?(attr)
    __send__("#{attr}=", changed_attributes[attr])
    clear_attribute_changes([attr])
  end
end
set_attribute_was(attr, old_value) click to toggle source

Force an attribute to have a particular “before” value

# File lib/active_model/dirty.rb, line 336
def set_attribute_was(attr, old_value)
  attributes_changed_by_setter[attr] = old_value
end