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']

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

     # File lib/active_model/dirty.rb, line 109
109:     def changed
110:       changed_attributes.keys
111:     end

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

     # File lib/active_model/dirty.rb, line 101
101:     def changed?
102:       !changed_attributes.empty?
103:     end

     # File lib/active_model/dirty.rb, line 131
131:     def changed_attributes
132:       @changed_attributes ||= {}
133:     end

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

     # File lib/active_model/dirty.rb, line 117
117:     def changes
118:       changed.inject(HashWithIndifferentAccess.new){ |h, attr| h[attr] = attribute_change(attr); h }
119:     end

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

     # File lib/active_model/dirty.rb, line 126
126:     def previous_changes
127:       @previously_changed
128:     end

     # File lib/active_model/dirty.rb, line 143
143:       def attribute_change(attr)
144:         [changed_attributes[attr], __send__(attr)] if attribute_changed?(attr)
145:       end

     # File lib/active_model/dirty.rb, line 138
138:       def attribute_changed?(attr)
139:         changed_attributes.include?(attr)
140:       end

     # File lib/active_model/dirty.rb, line 148
148:       def attribute_was(attr)
149:         attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
150:       end

     # File lib/active_model/dirty.rb, line 153
153:       def attribute_will_change!(attr)
154:         begin
155:           value = __send__(attr)
156:           value = value.duplicable? ? value.clone : value
157:         rescue TypeError, NoMethodError
158:         end
159: 
160:         changed_attributes[attr] = value
161:       end

     # File lib/active_model/dirty.rb, line 164
164:       def reset_attribute!(attr)
165:         __send__("#{attr}=", changed_attributes[attr]) if attribute_changed?(attr)
166:       end