Example of Domain-Driven Design in Rails

README.md

Example of Domain-Driven Design in Rails

Object

Name	Layer	Type	Description
app/models/visitor_pass.rb	Domain	Aggregate	Pass-related domain
app/services/tracker_service.rb	Domain	Domain Service	Logic between door and visitor interaction
app/controllers/passes_controller.rb	Application	Use Case	The user flow of "pass" a door

Test

Name	Type	Description
features/door_track.feature	E2E	Verify the user flow work correctly
spec/services/tracker_service_spec.rb	Unit	Verify the business logic work correctly

door_track.feature

Feature: Track Door Visitors
  Background:
    Given there have some sensors
      | identifier       |
      | cb5a68b8bb2e29a1 |
    And there have some doors
      | name             |
      | Main Arena Right |
    And sensor "cb5a68b8bb2e29a1" is put in door "Main Arena Right"
    And there have some visitor
      | name   |
      | Aotoki |

  Scenario: Visitor "Aotoki" can pass the door "Main Arena Right"
    When "Aotoki" pass the "Main Arena Right" through sensor "cb5a68b8bb2e29a1"
    Then I can receive pass in response

passes_controller.rb

class PassesController < ActionController::API
  include ConferenceTracker::Deps['tracker_service']
  
  rescue_from ActiveRecord::RecordNotFound, with: :not_found
  rescue_from TrackerService::AccessDenied, with: :pass_access_denied
  
  def create
    visitor = Visitor.by_rfid(rfid: pass_params[:rfid])
    door = Door.by_sensor(identifier: pass_params[:identifier])
    pass = tracker_service.track(door, visitor: visitor)
    pass.save
    
    render json: {
      pass: {
        in: pass.in?
      }
    }
  end
  
  private
  
  def pass_params
    params.require(:pass).permit(:rfid, :identifier)
  end
end

tracker_service.rb

class TrackerService
  def track(door, visitor:)
    raise TrackerService::AccessDenied unless door.allow?(visitor)
    
    pass = VisitorPass.new(visitor: visitor)
    pass.build_event(door_id: door.id)
    pass
  end
end

tracker_service_spec.rb

RSpec.describe TrackerService do
  subject(:service) { described_class.new }
  
  describe '#track' do
    subject(:track) { service.track(door, visitor: visitor) }
    
    given_a_visitor(name: 'Aotoki')
    given_a_door_allow_visitors(visitors: [visitor])
    
    it { is_expected.to be_pass_out }
    it { is_expected.to be_a(VisitorPass)
      
    context 'when visitor not allowed' do
      given_a_door_not_allow_anyone
      
      it { expect { track }.to raise_error(TrackerService::AccessDenied) }
    end
  end
end

visitor_pass.rb

class VisitorPass
  def initialize(visitor:)
    @visitor = visitor
    @pending_events = []
  end
  
  def events
    PassEvent.where(visitor: @visitor)
  end
  
  def build_event(**attributes)
    @pending_events << events.build(**attributes)
  end
  
  def in?
    events.size.odd?
  end
  
  def save
    PassEvent.import @pending_events.slice!(0..-1)
  end
end