Module: ActiveModel::Dirty

Extended by:
ActiveSupport::Concern
Includes:
AttributeMethods
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 to implement ActiveModel::Dirty are to:

  • 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']

Instance Method Summary (collapse)

Methods included from ActiveSupport::Concern

append_features, extended, included

Methods included from AttributeMethods

#method_missing, #respond_to?

Dynamic Method Handling

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

Instance Method Details

- (Object) changed

List of attributes with unsaved changes. 

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


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

def changed
  changed_attributes.keys
end

- (Boolean) changed?

Do any attributes have unsaved changes? 

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

Returns:

  • (Boolean) 


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

def changed?
  !changed_attributes.empty?
end

- (Object) changed_attributes

Map of change attr => original value. 



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

def changed_attributes
  @changed_attributes ||= {}
end

- (Object) changes

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

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


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

def changes
  changed.inject(HashWithIndifferentAccess.new){ |h, attr| h[attr] = attribute_change(attr); h }
end

- (Object) previous_changes

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']}


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

def previous_changes
  @previously_changed
end