Diffable

Diffable provides a mixin that can be used to extend any ActiveRecord object to provide diff functionality. Calling the diff method compares the receiver against another object and returns a Hash of differences found (presented as a description of the changes between the second object and the receiver - as if trying to restore the calling object from its replacement).

Add this line to your application's Gemfile:

gem 'diffable'

And then execute:

$ bundle

Or install it yourself as:

$ gem install diffable

Require the gem in the source file that includes the relevant model code:

require 'diffable'

Use the include statement to add Diffable support to each model that needs it:

class ModelA < ActiveRecord::Base
  include Diffable
end

You can then call the diff method on any instance of that model class:

object1 = ModelA.new(:name => "test")
object2 = ModelA.new(:name => "test2")
difference = object1.diff(object2)

There are 3 different types of change that can be returned by the diff method: modified, new and deleted. These are indicated using a :change_type key/value within the results Hash.

When an object is flagged as modified, its identifier and any of the altered fields are returned, e.g.:

{:change_type => "modified", :id => 42, :name => "test1"}

When an object is flagged as new, only its identifier is returned. Sample output:

{:change_type => "new", :id => 42}

When an object is flagged as deleted, all of its attributes are returned in the diff Hash. Sample output:

{:change_type => "deleted", :id => 42, :name => "test", :desc => "db test"}

If there are any database fields that should not be returned as part of a deleted object's data, they can be excluded at the model level using set_excluded_fields:

class ModelB < ActiveRecord::Base
  include Diffable
  set_excluded_fields :ignore_me
end

If a field value should always be included as part of a modified object's data, this can be set at the model level using set_conditional_fields:

class ModelC < ActiveRecord::Base
  include Diffable
  set_conditional_fields :metadata, :history
end

If your model uses has_many or has_one, the changes to these dependent objects can also be captured by the diff method, provided that their model definitions also use the include Diffable statement (otherwise they will be ignored). However, you will also need to inform the model which field can be used to uniquely identify records within the set returned for a particular parent object using set_unique_within_group. This should be a generated field as :id is unlikely to be suitable.

class ModelD < ActiveRecord::Base
  include Diffable
  has_many :catalogue_entries
end

class CatalogueEntries < ActiveRecord::Base
  include Diffable
  belongs_to :model_d
  set_unique_within_group :generated_identifier
  
  ...
  
end

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request