Module: ActiveModel::Dirty

Extended by:
ActiveSupport::Concern
Includes:
AttributeMethods
Included in:
ActiveRecord::AttributeMethods::Dirty
Defined in:
activemodel/lib/active_model/dirty.rb

Overview

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

If you wish to also track previous changes on save or update, you need to add

@previously_changed = changes

inside of your save or update method.

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
    @previously_changed = changes
    @changed_attributes.clear
  end

end

Examples:

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_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

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 << 'y'
person.name_change    # => ['Bill', 'Billy']

Constant Summary

Constants included from AttributeMethods

AttributeMethods::CALL_COMPILABLE_REGEXP, AttributeMethods::NAME_COMPILABLE_REGEXP

Instance Method Summary collapse

Methods included from ActiveSupport::Concern

append_features, extended, included

Methods included from AttributeMethods

#attribute_missing, #method_missing, #respond_to?, #respond_to_without_attributes?

Dynamic Method Handling

This class handles dynamic methods through the method_missing method in the class ActiveModel::AttributeMethods

Instance Method Details

#changedObject

List of attributes with unsaved changes.

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

108
109
110
# File 'activemodel/lib/active_model/dirty.rb', line 108

def changed
  changed_attributes.keys
end

#changed?Boolean

Returns true if any attribute have unsaved changes, false otherwise.

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

100
101
102
# File 'activemodel/lib/active_model/dirty.rb', line 100

def changed?
  changed_attributes.any?
end

#changed_attributesObject

Map of change attr => original value.


130
131
132
# File 'activemodel/lib/active_model/dirty.rb', line 130

def changed_attributes
  @changed_attributes ||= {}
end

#changesObject

Map of changed attrs => [original value, new value].

person.changes # => {}
person.name = 'bob'
person.changes # => { 'name' => ['bill', 'bob'] }

116
117
118
# File 'activemodel/lib/active_model/dirty.rb', line 116

def changes
  HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
end

#previous_changesObject

Map of attributes that were changed when the model was saved.

person.name # => 'bob'
person.name = 'robert'
person.save
person.previous_changes # => {'name' => ['bob, 'robert']}

125
126
127
# File 'activemodel/lib/active_model/dirty.rb', line 125

def previous_changes
  @previously_changed
end