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

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_change    # => ["Bill", "Bill"]
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

#attribute_changed?(attr) ⇒ Boolean

Handle *_changed? for method_missing.

Returns:

  • (Boolean)

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# File 'activemodel/lib/active_model/dirty.rb', line 146

def attribute_changed?(attr)
  changed_attributes.include?(attr)
end

#attribute_was(attr) ⇒ Object

Handle *_was for method_missing.


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# File 'activemodel/lib/active_model/dirty.rb', line 151

def attribute_was(attr)
  attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
end

#changedObject

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

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

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# File 'activemodel/lib/active_model/dirty.rb', line 111

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

Returns:

  • (Boolean)

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

def changed?
  changed_attributes.present?
end

#changed_attributesObject

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"}

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# File 'activemodel/lib/active_model/dirty.rb', line 141

def changed_attributes
  @changed_attributes ||= {}
end

#changesObject

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"] }

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# File 'activemodel/lib/active_model/dirty.rb', line 121

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

#previous_changesObject

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"]}

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

def previous_changes
  @previously_changed
end