Domain Driven Design and Hexagonal Architecture with Rails

You know that Domain Driven Design, Hexagonal Architecture, and the Single Responsibility Principle are important but it’s hard to know how to best apply them to Rails applications. Following the path of least-resistance will get you in trouble. In this session you will learn a way out of the “fat model, skinny controller” hell. You will leave with a roadmap to guide your design based on concepts from Domain Driven Design and Hexagonal Architecture.

This presentation was co-presented with Declan Whelan. More about Declan:

"Declan loves to code and help others get joy from their code. When not coding he is the CTO at Printchomp, an agile coach at Leanintuit and an Agile Alliance Board Member."

Transcript

2. 1. Embrace complexity
3. 2. Know where you’re going
4. 3. Be more than just a “Rails Developer”
5. app ├── assets ├── controllers ├── helpers ├── mailers ├── models └── views
6. V C M
7. V C M
8. def pricing_range_fold_and_save(new_range) pos = 0 pricings = self.product_pricings other_range = ProductPricing.new if pricings.length == 0 pricings.push(new_range) else pricings.each_with_index do |e, i| if i == 0 && new_range.start_date < e.start_date pricings.unshift(new_range) if new_range.end_date <= e.end_date e.start_date = new_range.end_date + 1.day break else while pricings[1].present? && new_range.end_date >= pricings[1].end_date pricings[1].destroy pricings.delete pricings[1] end if pricings[1].present? pricings[1].start_date = new_range.end_date + 1.day end break end elsif new_range.start_date <= e.end_date && new_range.start_date >= e.start_date ! if new_range.end_date < e.end_date other_range = e.dup other_range.start_date = new_range.end_date + 1.day if new_range.start_date == e.start_date e.destroy pricings.delete e i -= 1 else e.end_date = new_range.start_date - 1.day end pricings.insert(i+1, new_range) pos = i+1 pricings.insert(i+2, other_range) break else if new_range.start_date == e.start_date e.destroy pricings.delete e i -= 1 else e.end_date = new_range.start_date - 1.day end pricings.insert(i+1, new_range) pos = i+1 while pricings[i+2].present? && new_range.end_date >= pricings[i+2].end_date pricings[i+2].destroy pricings.delete pricings[i+2] end if pricings[i+2].present? pricings[i+2].start_date = new_range.end_date + 1.day end break end ! elsif i == pricings.size-1 pricings[i].end_date = new_range.start_date-1.day pricings.push(new_range) break end end end ! pricings.each_with_index do |pricing, i| if i != pricings.size-1 && pricing.price ==pricings[i+1].price pricing.end_date = pricings[i+1].end_date end if i != 0 && pricing.end_date == pricings[i-1].end_date pricing.destroy pricings.delete pricing end if pricing.end_date < pricing.start_date pricing.destroy pricings.delete pricing end end ! pricings.each do |pricing| if pricing != pricings[pos] pricing.currency = pricings[pos].currency pricing.save end end pricings[pos].save return pricings ! end
9. Pencil Sharpener
11. ! C V M
12. E E S S C V M R Application Domain S
14. Complexity The critical complexity of most software projects is in understanding the domain itself. ! Eric Evans
15. Ubiquitous Language
16. Domain Driven Design
17. Hexagonal Architecture
18. http://blog.mattwynne.net/2012/05/31/hexagonal-rails-objects-values-and-hexagons/ Matt Wynne
19. Form Object FO world C
20. Form Object FO world C
22. class TicketForm! include ActiveModel::Model! ! validates :trip, :price, :passengers, presence: true! ! def passengers! @passengers ||= [Passenger.new]! end! ! def tickets! @tickets ||= self.passengers.map do |passenger|! Ticket.new(...)! end! end! end!
23. class TicketsController < ApplicationController! ! def create! @ticket_form = TicketForm.new(params)! tickets = @ticket_form.tickets! ! if @ticket_form.valid? && TicketCharger.new(tickets).charge!! redirect_to success_url! else! render 'new'! end! end! ! end
24. Request Object RO C world
25. Request Object RO C world
26. class CreateOrderRequest ! include Virtus.value_object include ActiveModel::Validations ! attribute :customer, Customer validates :customer, nested: true, presence: true ! attribute :billing, Billing validates :billing, nested: true, presence: true ! attribute :shipping, Shipping validates :shipping, nested: true, presence: true ! end
27. class ApplicationController < ActionController::Base before_filter :validate_request ! def validate_request handle_error(request_object) unless request_object.valid? end ! def request_object @request_object ||= request_class.new(request_parameters) end ! def request_class "#{action_name}#{resource_name}Request".constantize end ! def handle_error(request_object) [...] end end
28. Service Object SO world C
29. Service Object SO world C
30. class OrderService ! def create(order) authorize!(order) ! repository.save!(order) ! purchase(order) do |transaction| repository.save!(order) end end ! def purchase(order, &block) PaymentService.new.purchase(order, &block) end ! end
31. class OrdersController < ApiController ! def create order = request_object.to_order transaction = OrderService.new.create(order) ! if transaction.success? order_created(order) else payment_failed(transaction) end end ! end
32. OK, so now what?
33. “I’m right there in the room, and no one even acknowledges me.”
34. E E S S C V M R Application Domain S
35. Repository M S R E
36. class Repository! ! class << self! ! attr_accessor :mapper! ! def save!(domain)! record = mapper.export(domain, record)! response = record.save!! domain.id = record.id! response! end! ! end! ! def self.method_missing(method_name, *args, &block)! Scope.new(mapper).send(method_name, *args, &block)! end! ! end
37. class Scope! ! attr_accessor :mapper, :scope! ! def initialize(mapper)! @mapper = mapper! @scope = mapper.export_class! end! ! def method_missing(method_name, *args, &block)! @scope = scope.send(method_name, *args, &_map_block(block))! ! scope.is_a?(ActiveRecord::Relation) ? self : _map(scope)! end! ! def _map_block(block)! Proc.new { |*args| block.call(_map(*args)) } if block! end! ! def _map(object)! if object.is_a?(mapper.export_class)! mapper.map(object)! elsif object.is_a?(Enumerable)! object.map { |e| e.is_a?(mapper.export_class) ? mapper.map(e) : e }! else! object! end! end! ! def respond_to?(method_name, include_private = false)! scope.respond_to?(method_name, include_private) || super! end! end
38. class Mapper! class << self! ! attr_reader :base_class, :export_class! ! def maps(mapping)! @base_class, @export_class = mapping.first! end! ! def map(object)! if object.is_a? base_class! export(object)! else! import(object)! end! end! ! def export(base, record=nil)! return unless base! ! if record! record.assign_attributes(base.attributes)! else! record = export_class.new(base.attributes)! end! ! record! end! ! def import(record)! base_class.new(record.attributes) if record! end! end! end!
39. class Repository! ! class << self! ! attr_accessor :mapper! ! def save!(domain)! record = IdentityMap.get(mapper.export_class, domain.id)! record = mapper.export(domain, record)! response = record.save!! IdentityMap.add(record)! domain.id = record.id! response! end! ! end! ! def self.method_missing(method_name, *args, &block)! Scope.new(mapper).send(method_name, *args, &block)! end! ! end
40. class IdentityMap! ! class << self! def add(record)! raise ArgumentError.new('Record cannot be added with a nil id') unless record.id! repository[key(record.class)][record.id] = record! end! ! def remove(record)! repository[key(record.class)].delete(record.id)! end! ! def get(klass, id)! repository[key(klass)][id]! end! ! def clear! repository.clear! end! ! def repository! Thread.current[:identity_map] ||= Hash.new { |h,k| h[k] = {} }! end! ! def key(klass)! klass! end! ! end! end!
41. So, what’s the point again?
42. 1. Embrace complexity ! 2. Know where you’re going ! 3. Be more than just a “Rails Developer”
43. https://github.com/dwhelan/hex-ddd Continue the discussion
44. Reading Patterns of Enterprise Application Architecture
 Martin Fowler Domain Driven Design
 Tackling Complexity in the Heart of Software
 Eric Evans Practical Object Oriented Design in Ruby
 An Agile Primer
 Sandi Metz
45. Reading Clean Code
 A Handbook of Agile Software Craftsmanship
 Robert C. Martin Implementing Domain Driven Design
 Vaughn Vern
46. Photo/Video Credits https://www.youtube.com/watch?v=-JLbAePwoHQ http://www.docstoc.com/docs/47342986/Rube-Goldberg-Project-Rube https://sitespecific2013awe.blogs.lincoln.ac.uk/tag/tower-of-babel/ http://collabcubed.com/2012/01/17/roskilde-festival-plywood-dome/ http://mitchjackson.com/white-elephants/