Polidef

Still a WIP v1.0.0 is planned for early March 2024

Polidef allows you to create easily testable policy objects that can be very generic for use in multiple objects or be very very specific all while avoiding heavy scaffolding in code.

This gem isn't recommended for newer applications that are still working through determining their domain as something like this can end up complicating features more so than it can help. The target audience is for those who have inherited a more mature codebase where the code design is not always ideal. The abstraction here can help provide you with ways of naming important "conditional based" concepts in your domain, especially those that tend to grow with more and more &&s or ||s.

The techniques here are certainly implementable with POROs (Plain Old Ruby Objects) but the convinence of these abstractions, especially for testing maybe useful.

Add this line to your application's Gemfile:

gem 'polidef'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install polidef

As of Feb 2024, this project is still a WIP. I've tried to notate available API's as they are on the main branch but it may not always be accurate.

The simpilest way to implement a Polidef::Policy is to create a class which implements a #policy method that evaluates to the truthy version of your logic. Think along the lines of:

"ThisObject can_do_this if Policy is fulfilled"

Policy Object

class NotificationPolicy < Polidef::Policy
  dependencies :user, :subject, :channel
  
  def policy
    policy_chain([:user_can_recieve?, :channel_usable?])
      .or_policy(:subject_overrides_preferences?)
  end
  
  private
  
  def user_can_recieve?
    user.prefences.notifications_enabled? && !user.notifications_muted?
  end
  
  def channel_usable?
    channel.state == 'active'
  end
  
  def subject_overrides_preferences?
    subject.overrides_notification_policy?
  end
end

We can then use NotificationPolicy where ever we need to in a few different ways:

# ...
include Polidef::Policies
## a block
def send_notification_to(recipient, notifier: NotificationService)
  with_fulfilled_policy(:notification_policy, dependencies: {user: recipient, subject: self, channel: channel}) do
    notifier.send_notification_to(recipient, subject: subject)
  end
end

## a method
def send_notification_to(recipient, notifier: NotificationService)
  if policy_fulfilled?(:notification_policy, user: recipient, subject: self, channel: channel)
    notifier.send_notification_to(recipient, subject: subject)
  else # policy implicitely rejected
    notifier.perform_later(current_user.time_till_unmute, user_id: current_user.id subject_id: subject.id, channel_id: channel.id)
  end
end

Testing the NotificationPolicy is simple with the provided assertions. Since we want to know if the #send_notification works and don't care about the specifics of the NotificationPolicy and/or we don't want to have to mock/stub (or worse, persist) each dependency for the test we can instead, use asserts_with_policy.

# ...
include Polidef::PolicyAssertions

# ...

def test_send_notification_for
  message = build(:message_in_default_channel, content: "Test")

  mock_notification_service = Minitest::Mock.new
  mock_notification_service.expects(:send_notification_to, nil, [User], subject: message)
  
  # Forces Policy fulfilled
  assert_with_fulfilled_policy :notification_policy do
    message.send_notification_to(@user, notifier: mock_notification_service)
  end
  
  assert_mock mock_notification_service
end

def test_send_notification_for
  message = build(:message_in_default_channel, content: "Test")

  mock_notification_service = Minitest::Mock.new
  mock_notification_service.expects(:perform_later, 'job-id-123', [Time], Hash)
  
  # Forces Policy rejected
  assert_with_rejected_policy :notification_policy do
    message.send_notification_to(@user, notifier: mock_notification_service)
  end

  assert_mock mock_notification_service
end

• Support for inline Policy declarations (50% complete)
• Support for policy_rejected inverse of fulfilled methods
• Support for decorators using SimpleDelegator for very generic policies
• Useful testing API to test individual Policies
• Support for rails generate policy --deps dep_1, dep_2 ...
• "Conditional chaining" API for readability

• More thorough examples
• Integrate a documentation framework (RDoc and Yard maybe?)
• A small static site
• Issue & PR templates

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/juliusdelta/polidef. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the Polidef project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.