A full-stack programming model for Ruby and Event Sourcing

Exploring a full stack programming model for Ruby and Event Sourcing, including a time-based approach to domain modelling, durable workflows, time-travelling and reactive server-rendered UIs.

Transcript

1. A full-stack programming model for Ruby and Event Sourcing. Ismael Celis ismaelcelis.com
5. How do I order a cup of coffee?
6. # POST /orders/:id/line_items def create order = Order.find(params[:id]) order.line_items.create(line_item_params) redirect_to order_url(order) end
7. # A background job class OrderArchivalJob def perform(order_id) order = Order.find(order_id) order.archive end end
8. # A CLI task bin/rake orders:archive
9. Timelines
10. Start order [ business rules ] Order started Time
11. Add item [ business rules ] Item added Start order [ business rules ] Order started Update quantity [ business rules ] Quantity updated
12. eventmodelling.org Start order Order started commands state views events Time Order 1 "order-1" "order-1"
13. eventmodelling.org Add item Item added commands state views events Time Order 1 1. latte latte latte
14. Event Sourcing 101
15. 1. Order started 2. Product added 3. Product added 4. Quantity updated Past events Your order (v4) Latte (2) Croissant (1) Current state
16. Initial
 Travel budget
 Flight
 Hotel room
 Bus ticket Balance
 Events Current state €0.00
 + €1,000.00
 - €300.00
 - €100.00
 - €1.50 €598.50
17. 1. Order started 2. Product added 3. Product added 4. Quantity updated Time "order-123" 1. Order started 2. Product added 3. Quantity updated "order-333" Your order (v4) Latte (2) Croissant (1) Your order (v3) Yoghurt (1)
19. OrderStarted = Data.define ItemAdded = Data.define(:product_id, :name, :price) ItemQuantityUpdated = Data.define(:product_id, :quantity) events = [ OrderStarted.new, ItemAdded.new('latte', 'Latte', 300), ItemQuantityUpdated.new('milk', 2) ]
20. initial_order = { status: nil, items: {} }
21. order = events.each.with_object(initial_order.dup) do |order, event| case event when OrderStarted order[:status] = 'open' when ItemAdded product_id = event.product_id image = event.image price = event.price order[:items][product_id] = {name:, price:, quantity: 1} when QuantityUpdated # etc end end
22. order = events.each.with_object(initial_order.dup) do |order, event| case event when OrderStarted order[:status] = 'open' when ItemAdded product_id = event.product_id image = event.image price = event.price order[:items][product_id] = {name:, price:, quantity: 1} when QuantityUpdated # etc end end
23. order = events.each.with_object(initial_order.dup) do |order, event| case event when OrderStarted order[:status] = 'open' when ItemAdded product_id = event.product_id image = event.image price = event.price order[:items][product_id] = {name:, price:, quantity: 1} when QuantityUpdated # etc end end
24. order[:items][‘latte'][:quantity] # => 2
25. Current state Event store 1 2 3 4 5 6 Validations Command fetch past events append new events
27. Current state Event store 1 2 3 4 5 6 Command Command model Query model UI Command Query Responsibility Segregation
28. Back to timelines
29. Add item Item added commands state views events Time Order 1 1. latte latte latte
30. An implementation (WIP) github.com/ismasan/sourced
31. class OrderState LineItem = Struct.new(:product_id, :name, :price, :quantity) attr_reader :id, :status, :items def initialize(id) @id = id @status = 'new' @items = {} end def add_item(product_id, **rest) @items[product_id] = LineItem.new(product_id, **rest) end def total = items.sum { |it| it.price * it.quantity } end
32. order = OrderState.new(‘order-123') order.add_item( product_id: ‘latte', name: 'Latte', price: 100, quantity: 2 ) order.total # => 200
33. AddItem = Sourced::Command.define('orders.add_item') do attribute :product_id, String attribute :name, String attribute :price, Integer attribute :quantity, Integer end ItemAdded = Sourced::Event.define('orders.item_added') do attribute :product_id, String attribute :name, String attribute :price, Integer attribute :quantity, Integer end
34. class OrderActor < Sourced::Actor state do |stream_id| OrderState.new(stream_id) end command AddItem do |order, cmd| # Validate business rules raise 'order is not open' unless order.status == 'open' raise 'order can have up to 5 products' if cart.items.size == 5 event ItemAdded, cmd.payload end event ItemAdded do |order, event| order.add_item(**event.payload) end end
35. class OrderActor < Sourced::Actor state do |stream_id| OrderState.new(stream_id) end command AddItem do |order, cmd| # Validate business rules raise 'order is not open' unless order.status == 'open' raise 'order can have up to 5 products' if order.items.size == 5 event ItemAdded, cmd.payload end event ItemAdded do |order, event| order.add_item(**event.payload) end end
36. class OrderActor < Sourced::Actor state do |stream_id| OrderState.new(stream_id) end command AddItem do |order, cmd| # Validate business rules raise 'order is not open' unless order.status == 'open' raise 'order can have up to 5 products' if cart.items.size == 5 event ItemAdded, cmd.payload end event ItemAdded do |order, event| order.add_item(**event.payload) end end
37. command AddItem do |state, cmd| return unless state.open? event ItemAdded, cmd.payload end event ItemAdded do |state, event| state.add_item(**event.payload) end
38. Work fl ows
39. Add item Item added Open orders commands state events Time Update quantity Quantity updated Cashier Latte, Demi Latte, Demi quantity: 2 quantity: 2
40. Barista Open orders Time Place order Order placed Cashier Placed orders Fulfil item Item fulfilled
42. Projections
43. class OrderListings < Sourced::Projector::EventSourced state do |stream_id| { id: stream_id, status: nil, items: {} } end event Order::Placed do |listing, event| listing[:status] = 'placed' end # Evolve listing record from events event Order::ItemAdded do |listing, event| listing[:items][event.payload.product_id] = 'open' end # Sync listing record to a file sync do |listing, _, _| File.write("/listings/#{listing[:id]}.json", JSON.dump(listing)) end end
44. class OrderListings < Sourced::Projector::EventSourced state do |stream_id| { id: stream_id, status: nil, items: {} } end event Order::Placed do |listing, event| listing[:status] = 'placed' end # Evolve listing record from events event Order::ItemAdded do |listing, event| listing[:items][event.payload.product_id] = 'open' end # Sync listing record to a file sync do |listing, _, _| File.write("/listings/#{listing[:id]}.json", JSON.dump(listing)) end end
45. class OrderListings < Sourced::Projector::EventSourced state do |stream_id| { id: stream_id, status: nil, items: {} } end event Order::Placed do |listing, event| listing[:status] = 'placed' end # Evolve listing record from events event Order::ItemAdded do |listing, event| listing[:items][event.payload.product_id] = 'open' end # Sync listing record to a file sync do |listing, _, _| File.write("/listings/#{listing[:id]}.json", JSON.dump(listing)) end end
46. class OrderListings < Sourced::Projector::EventSourced state do |stream_id| { id: stream_id, status: nil, items: {} } end event Order::Placed do |listing, event| listing[:status] = 'placed' end event Order::ItemAdded do |listing, event| listing[:items][event.payload.product_id] = 'open' end event Order::ItemFulfillmentStarted do |listing, event| listing[:items][event.payload.product_id] = 'started' end event Order::ItemFulfilled do |listing, event| listing[:items][event.payload.product_id] = ‘fulfilled' end # Sync listing record to a file
47. listing[:status] = 'placed' end # Evolve listing record from events event Order::ItemAdded do |listing, event| listing[:items][event.payload.product_id] = 'open' end # Sync listing record to a file sync do |listing, _, _| File.write("/listings/#{listing[:id]}.json", JSON.dump(listing)) end end
48. Concurrent work fl ows
49. Start Payment Payment confirmed "order-1" "order-1-payment" Confirm payment Payment confirmed Time Payment started Start Payment Payments API Fulfil item Item fulfiled
50. class OrderActor < Sourced::Actor # etc event PaymentStarted do |state, event| state.payment.status = :started state.payment.id = event.payload.payment_id end reaction PaymentStarted do |state, event| stream = stream_for(“#{state.id}-payment”) stream.command( Payment::Start, order_id: state.id, amount: state.total.cents ) end end
51. class OrderActor < Sourced::Actor # etc event PaymentStarted do |state, event| state.payment.status = :started state.payment.id = event.payload.payment_id end reaction PaymentStarted do |state, event| stream = stream_for(state.payment.id) stream.command( Payment::Start, order_id: state.id, amount: state.total.cents ) end end
52. class Payment < Sourced::Actor State = Struct.new(:id, :order_id, :amount, :status, :created_at) Start = Sourced::Command.define(...) Started = Sourced::Command.define(...) state do |id| State.new(id, nil, 0, :pending, nil) end command Start do |state, cmd| event :started, cmd.payload end event Started do |state, event| # update local state end # etc end
53. class Payment < Sourced::Actor # etc... reaction Started do |state, event| response = PaymentsAPI.pay(event.payload) order_stream = stream_for(event) if response.ok? order_stream.command Order::ConfirmPayment else order_stream.command Order::FailPayment end end end
54. Payment::Start Payment::Started .reaction(Payment::Started) .command(Order::PaymentConfirmed) "order-1-payment" Payments API "order-1"
56. Event correlation
57. Order::PaymentStarted Order::StartPayment id: A causation_id: A correlation_id: A id: B causation_id: A correlation_id: A Payment::Start id: C causation_id: B correlation_id: A Payment::Started id: D causation_id: C correlation_id: A
59. Automation
60. Confirm payment Payment confirmed Order fulfilled Deliverable orders Deliver order Order delivered fulfilled ✓ paid ✓ delete Fulfil order Employee
61. state do |id| { id:, fulfilled: false, paid: false, status: 'pending' } end event Order::OrderFulfilled do |state, event| state[:fulfilled] = true check_deliverable(state) end event Order::PaymentConfirmed do |state, event| state[:paid] = true check_deliverable(state) end event Order::OrderDelivered do |state, event| state[:status] = 'delivered' end
62. private def check_deliverable(state) state[:status] = 'ready' if state[:fulfilled] && state[:paid] end
64. Confirm payment Payment confirmed Order fulfilled Deliverable orders Deliver order Order delivered fulfilled ✓ paid ✓ delete Fulfil order Automation
65. event Order::OrderDelivered do |state, event| state[:status] = 'delivered' end reaction do |state, event| return unless state[:status] == 'ready' stream_for(event).command(Order::DeliverOrder) do |cmd| cmd.delay Time.now + 5 # Simulate a delay for delivery end end private def check_deliverable(state) state[:status] = 'ready' if state[:fulfilled] && state[:paid] end
67. Reactive UI
68. Reactive UI
69. Sourced::UI::Components::Command(Order::Place) do |form| form.submit(type: 'submit', class: 'btn') { 'Place order' } end phlex.fun
70. post '/commands' do cmd = command_context.build(params[:command]) Sourced.schedule_commands([cmd]) halt 204 end
71. # GET /updates when OrderListings::System::Updated if sse.signals['page_key'] == 'Pages::CashierPage' sse.merge_fragments Components::OrdersTable.new( orders: OrderListings.all ) end end data-star.dev phlex.fun
72. The future * Fix bugs! * State Charts - https://statecharts.dev * Durable execution * SQLite backend * Auto-generated diagrams and docs
73. Extras
74. Rebuilding
 Projections
78. Command handlers Event store Command bus Reactions Projectors reactors Emails APIs Projections Caches schedule command schedule command
79. command Place do |state, cmd| return unless state.open? event Placed, cmd.payload end event Placed do |state, event| state.status = :placed end