Module: ActiveModel::Dirty

Extended by:
ActiveSupport::Concern
Includes:
AttributeMethods
Defined in:
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 AttributeMethods

#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

#changed ⇒ Object

List of attributes with unsaved changes.

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



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

def changed
  changed_attributes.keys
end

#changed? ⇒ Boolean

Do any attributes have unsaved changes?

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

Returns:

  • (Boolean) 


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

def changed?
  !changed_attributes.empty?
end

#changed_attributes ⇒ Object

Map of change attr => original value.



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

def changed_attributes
  @changed_attributes ||= {}
end

#changes ⇒ Object

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

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



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

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

#previous_changes ⇒ Object

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 'lib/active_model/dirty.rb', line 126

def previous_changes
  @previously_changed
end