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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 reset_changes when you want to reset the changes information.

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
    # do persistence work
    changes_applied
  end

  def reload!
    reset_changes
  end
end

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_changed?(from: "Uncle Bob", to: "Bob") # => 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

Reset the changes:

person.previous_changes # => {"name" => ["Uncle Bob", "Bill"]}
person.reload!
person.previous_changes # => {}

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_change    # => ["Bill", "Bill"]
person.name << 'y'
person.name_change    # => ["Bill", "Billy"]
Methods
C
P
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"]
# File activemodel/lib/active_model/dirty.rb, line 118
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 109
def changed?
  changed_attributes.present?
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 148
def changed_attributes
  @changed_attributes ||= ActiveSupport::HashWithIndifferentAccess.new
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 128
def changes
  ActiveSupport::HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
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 138
def previous_changes
  @previously_changed ||= ActiveSupport::HashWithIndifferentAccess.new
end