Navigable

Navigable is a stand-alone tool for isolating business logic from external interfaces and cross-cutting concerns. Navigable composes self-configured command and observer objects to allow you to extend your business logic without modifying it. Navigable is compatible with any Ruby-based application development framework, including Rails, Hanami, and Sinatra.

Installation

Add this line to your application's Gemfile:

gem 'navigable'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install navigable

Usage

We built Navigable to help separate the web adapter and persistence layer from your actual business logic. And, we did it in a composable manner that allows for incredible flexibility. Here's a peek:

# CreateAlert command
class CreateAlert
  extend Navigable::Command

  corresponds_to :create_alert
  corresponds_to :create_alert_and_notify

  def execute
    return failed_to_validate(new_alert) unless new_alert.valid?
    return failed_to_create(new_alert) unless created_alert.persisted?

    successfully created_alert
  end

  private

  def new_alert
    @new_alert ||= Alert.new(params)
  end

  def created_alert
    @created_alert ||= @new_alert.save
  end
end

# AllRecipientsNotifier observer
class AllRecipientsNotifier
  extend Navigable::Observer

  observes :create_alert_and_notify

  def on_success(alert)
    NotifyAllRecipientsWorker.perform_async(alert_id: alert.id)
  end
end

In these two classes, Navigable enables you to execute multiple use cases. You can create an alert:

Navigable::Dispatcher.dispatch(:create_alert, params: alert_params)

Or, create an alert and notify all recipients:

Navigable::Dispatcher.dispatch(:create_alert_and_notify, params: alert_params)

All without having to add conditional logic about the notifications to the CreateAlert class.

Similarly, you can add cross-cutting concerns to an application just as easily:

# Monitor observer
class Monitor
  extend Navigable::Observer

  observes_all_commands

  def on_success(*args)
    increment_counter(observed_command_key, :success)
  end

  def on_failed_to_validate(*args)
    increment_counter(observed_command_key, :failed_to_validate)
  end

  def on_failed_to_create(*args)
    increment_counter(observed_command_key, :failed_to_create)
  end

  # ...
end

Here are a few things to look for in the code above:

• The DSL in the execute method of the CreateAlert class is built into Navigable. Methods like successfully tell Navigable the results of the command so that it can notify the observers.

• The two corresponds_to statements in CreateAlert tell Navigable to execute that command when either key is dispatched. You can register a command under as many different keys as you need.

• The single observes statement in AllRecipientsNotifier class tells Navigable to send a message to that class only when the :create_alert_with_notifications key is dispatched. One observer can observe as many commands as you need. And, many observers can observe the same command.

• Use the observes_all_commands statement (as shown in the Monitor class) for cross-cutting concerns. It tells Navigable to send messages to the observer no matter which command was executed.

For a deeper look at the core concepts introduced by Navigable, please have a look at our wiki.

Rails Usage

The code above can be integrated into Rails like this:

# AlertsController
class AlertsController < ApplicationController
  # ...

  def create
    @alert = Navigable::Dispatcher.dispatch(:create_alert, params: alert_params)

    if @alert.persisted?
      redirect_to @alert, notice: 'Alert successfully created.'
    else
      render :new
    end
  end

  # ...
end

# Alert model
class Alert < ApplicationRecord
  validates :title, presence: true
end

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/first-try-software/navigable.

License

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

Code of Conduct

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