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Events. Events. Events!

Events. Events. Events!

My talk about event sourcing in ruby from wrocloverb (https://wrocloverb.com)

Anton Davydov

March 24, 2019
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  1. View Slide

  2. View Slide

  3. 3 days of afterparty

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  4. View Slide

  5. View Slide

  6. Hello Wroclaw.rb

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  7. Fist time in Poland

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  8. View Slide

  9. View Slide

  10. What I know now

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  11. Pierogi

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  12. Pelmeni -> Pierogi z mięsem
    Varenyky -> Pierogi ruskie

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  13. Best state machine
    implementation

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  14. class State
    def method_missing(method, *args, &block)
    eval(method.to_s.capitalize).send(:new)
    end
    end
    class Created < State; end
    class Open < State; end
    class Closed < State; end

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  15. Event Sourcing is popular

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  16. View Slide

  17. Memes is not

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  18. View Slide

  19. Autoload is still

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  20. Awesome people and community

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  21. Anton Davydov
    github.com/davydovanton

    twitter.com/anton_davydov
    davydovanton.com

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  22. View Slide

  23. • Software developer at Hippo
    • OpenSource evangelist
    • Hanami core developer
    • Try to make own product
    • Technical consulting

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  24. Stickers

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  25. • Coffee
    • Beer
    • Psychology
    • SW-2039-0208-4228
    • How to draw images for presentations
    • Bad stories

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  26. • Coffee
    • Beer
    • Psychology
    • SW-2039-0208-4228
    • How to draw images for presentations
    • Bad stories

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  27. Tried to be writer and make a story

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  28. expectations

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  29. reality

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  30. But I got help from my friend

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  31. Meet George

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  32. He is quiet and love ask questions

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  33. View Slide

  34. View Slide

  35. Events

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  36. View Slide

  37. View Slide

  38. View Slide

  39. Git

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  40. Each commit - something
    which was happened

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  41. View Slide

  42. Each commit contain
    description and changes
    (payload)

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  43. View Slide

  44. What happened

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  45. Payload

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  46. List of cart items which
    user deleted and added

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  47. Activity audit

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  48. Don’t delete deleted data

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  49. deleted_at

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  50. But usually we’re working with
    current state of application

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  51. actions -> events
    data in DB -> current state

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  52. actions -> events
    data in DB -> current state

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  53. Knok knok

    George

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  54. George

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  55. What will happen if we
    change it?

    George

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  56. Store events

    George

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  57. And calculate current
    state when we need it

    George

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  58. Event Sourcing

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  59. Store what was happened
    instead current state

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  60. And get state when you need

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  61. Where to store?

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  62. Event storage

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  63. Can be anything

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  64. View Slide

  65. Rules

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  66. Event was happened

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  67. Immutable events

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  68. Can’t delete or update event

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  69. View Slide

  70. View Slide

  71. View Slide

  72. Only valid data in the events

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  73. View Slide

  74. View Slide

  75. View Slide

  76. View Slide

  77. View Slide

  78. Data evolution

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  79. View Slide

  80. View Slide

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  82. View Slide

  83. View Slide

  84. Stop

    George

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  85. We can break the app!

    George

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  86. >_<

    George

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  87. Pro tips: optional fields,
    binary data structures

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  88. more in the book

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  89. How to get state from
    event store?

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  90. We need to calculate it
    using current event list

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  91. Projections

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  92. project(projection, events, init_state) -> state

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  93. project(projection, events, init_state) -> state
    same as a block in ruby’s enumerator

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  94. project(projection, events, init_state) -> state
    pure function

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  95. View Slide

  96. View Slide

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  100. View Slide

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  102. View Slide

  103. View Slide

  104. View Slide

  105. View Slide

  106. View Slide

  107. We’re compile current state for
    all events each time

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  108. George

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  109. We can’t store all data for
    last 10 years

    George

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  110. And will have a
    performance issues for
    getting current state ▼
    George

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  111. How to fix it?

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  112. Streams!

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  113. View Slide

  114. Event bus#1
    Event bus#1
    Event bus#2
    Event bus#1
    Event bus#2
    Event bus#2

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  115. Event stream: bus#1
    Event stream: bus#1
    Event stream: bus#2
    Event stream: bus#1
    Event stream: bus#2
    Event stream: bus#2

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  116. Stream: bus#1

    Event stream: bus#1
    Event stream: bus#1
    Event stream: bus#1

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  117. Stream: bus#2

    Event stream: bus#2
    Event stream: bus#2
    Event stream: bus#2

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  118. Pros: less events for processing

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  119. Cons: one more abstraction

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  120. Add snapshot for the current
    data state!

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  121. project(function, events, state) -> state

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  122. project(function, events, state) -> state
    {}

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  123. project(function, events, state) -> state
    { users: […] }

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  124. View Slide

  125. View Slide

  126. View Slide

  127. View Slide

  128. View Slide

  129. View Slide

  130. You can use any DB as a cache

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  131. View Slide

  132. Idea: use more that one DB
    for cache

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  133. Relation DB for search and index
    page

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  134. Document oriented DB for show
    page

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  135. Real world

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  136. Where it can be useful

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  137. E-comerse systems

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  138. Order and checkout flow

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  139. Something where you need
    version control
    (wiki, docs, group editing)

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  140. Domain depends on events
    (tracking systems)

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  141. redux?

    George

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  142. Event sourcing and event
    driven architecture are
    different things

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  143. And they use events in
    different ways

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  144. ES -> event happened and I store it
    ED -> event happened and I say
    everyone it

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  145. Blockchain!

    George

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  146. pros

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  147. Easier to communicate with
    domain experts

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  148. • Logging out from box
    • Time traveling
    • Restore a state of system

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  149. • You don’t work with tables you work with
    events and changes
    • Experemental data structures
    • Easy to change database implementations

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  150. cons

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  151. • Hard for understand idea and
    complicated abstraction
    • Not popular in ruby
    • Developers need deprogramming

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  152. • Harder to get state than CRUD
    • Hard to understand the whole
    chain of events
    • Another architecture type

    with different DB structure

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  153. • Versions and versions
    compatibility
    • Updating or deleting
    events
    • Eventual Consistency

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  154. Advanced topics

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  155. How to display created data ASAP?

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  156. Solution 1

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  157. cheat user
    display real
    data

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  158. View Slide

  159. View Slide

  160. View Slide

  161. View Slide

  162. View Slide

  163. solution 2

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  164. WebSockets and Long Polling

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  165. How to make right events order?

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  166. View Slide

  167. View Slide

  168. View Slide

  169. View Slide

  170. distributed systems

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  171. more here

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  172. And here

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  173. How to delete user related data

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  174. Retroactive Event

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  175. View Slide

  176. Lose encrypted data key

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  177. How to use ES in ruby

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  178. Simple way

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  179. gems

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  180. View Slide

  181. github.com/zilverline/sequent

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  182. View Slide

  183. eventide-project.org

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  184. View Slide

  185. Brave way

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  186. Build all stuff by self

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  187. View Slide

  188. View Slide

  189. View Slide

  190. hanami-events

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  191. Event driven transport layer
    with event versions
    and types

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  192. Connection without global state

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  193. Hanami::Events.new(:memory_sync)
    Hanami::Events.new(:memory_async)
    Hanami::Events.new(:redis)

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  194. Hanami::Events::Adapter.register(:google_pubsub) do
    Google::PubSub
    end
    Hanami::Events.new(:google_pubsub)
    # => event instance with your google pubsub adapter

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  195. events = Hanami::Events.new(:memory_sync)
    events.broadcast('user.created', user: user)
    Broadcaster

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  196. events.subscribe('user.created') do |payload|
    puts payload
    end
    events.subscribe('user.*') do |payload|
    puts payload
    end
    events.subscribe(/\Auser\..*/) do |payload|
    puts payload
    end
    Subscriber

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  197. Event sourcing looks
    cool.

    George

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  198. But I have legacy app.
    How can I migrate?

    George

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  199. User add something to cart

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  200. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    if cart_repo.item_exist?(params[:item])
    item = CartItemRepository.new.create_copy(params[:item])
    else
    item = CartItemRepository.new.create(params[:item])
    end
    analytics.call('Item Added')
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  201. Step 1: Event Storming

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  202. Why?
    Detect important business
    events in the system

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  203. Orders::Events::ItemAdded
    Orders::Events::CoppyItemAdded

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  204. Step 2: store (apply) event

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  205. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    event_store.apply(Order::Events::ItemAdded.new(payload))
    if cart_repo.item_exist?(params[:item])
    item = CartItemRepository.new.create_copy(params[:item])
    else
    item = CartItemRepository.new.create(params[:item])
    end
    analytics.call('Item Added')
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  206. How to validate item?

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  207. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    event_store.apply(Orders::Events::ItemAdded.new(payload))
    if cart_repo.item_exist?(params[:item])
    item = CartItemRepository.new.create_copy(params[:item])
    else
    item = CartItemRepository.new.create(params[:item])
    end
    analytics.call('Item Added')
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  208. Step 3: calculate state

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  209. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    events = event_store.get_stream(params[:order_id])
    items = @project.call(Order::Projections::ItemList, events)
    if items.include?(params[:item])
    event_store.apply(Orders::Events::ItemAdded.new(payload))
    else
    event_store.apply(Orders::Events::CoppyItemAdded.new(payload))
    end
    analytics.call('Item Added')
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  210. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    events = event_store.get_stream(params[:order_id])
    items = @project.call(Order::Projections::ItemList, events, {})
    if items.include?(params[:item])
    event_store.apply(Orders::Events::ItemAdded.new(payload))
    else
    event_store.apply(Orders::Events::CoppyItemAdded.new(payload))
    end
    analytics.call('Item Added')
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  211. module Projections
    class AllTask
    def call(event, state)
    case event
    when Orders::Events::ItemAdded
    state[:orders] ||= []
    state[:orders] << event.payload
    when Orders::Events::ItemRemoved
    # ...
    end
    state
    end
    end
    end

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  212. module Projections
    class AllTask
    def call(event, state)
    case event
    when Orders::Events::ItemAdded
    state[:orders] ||= []
    state[:orders] << event.payload
    when Orders::Events::ItemRemoved
    # ...
    end
    state
    end
    end
    end

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  213. module Projections
    class AllTask
    def call(event, state)
    case event
    when Orders::Events::ItemAdded
    state[:orders] ||= []
    state[:orders] << event.payload
    when Orders::Events::ItemRemoved
    # ...
    end
    state
    end
    end
    end

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  214. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    events = event_store.get_stream(params[:order_id])
    items = @project.call(Order::Projections::ItemList, events, {})
    if items.include?(params[:item])
    event_store.apply(Orders::Events::ItemAdded.new(payload))
    else
    event_store.apply(Orders::Events::CoppyItemAdded.new(payload))
    end
    analytics.call('Item Added')
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  215. Step 4: subscribers

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  216. # analytics subscribers
    event_store.subscribe(Orders::Events::ItemAdded) do |event|
    analytics.call('Item removed', event.payload)
    end
    event_store.subscribe(Orders::Events::CoppyItemAdded) do |event|
    analytics.call(‘Copy of item added’, event.payload)
    end
    event_store.subscribe(Orders::Events::ItemRemoved) do |event|
    analytics.call(‘Item removed', event.payload)
    end

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  217. module Web::Controllers::CartItem
    class Create
    include Web::Action
    def call(params)
    halt(400) unless params.valid?
    events = event_store.get_stream(params[:order_id])
    items = @project.call(Order::Projections::ItemList, events, {})
    if items.include?(params[:item])
    event_store.apply(Orders::Events::ItemAdded.new(payload))
    else
    event_store.apply(Orders::Events::CoppyItemAdded.new(payload))
    end
    redirect_to routes.order_path(params[:order_id])
    end
    end
    end

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  218. Step 4: move logic to domain

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  219. PROFIT

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  220. pro tip: you can use ES only
    as a part of your system

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  221. What next?

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  222. View Slide

  223. View Slide

  224. SAGA PATTERN

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  225. Long business transactions

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  226. View Slide

  227. View Slide

  228. CQRS


    (Command Query
    Responsibility Segregation)

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  229. – Martin Fowler
    “You can use a different
    model to update information
    than the model you use to
    read information”

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  230. Looking outside
    ruby world

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  231. github.com/heynickc/
    awesome-ddd

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  232. github.com/davydovanton/event_sourcing_ruby

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  233. DDD

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  234. Again?

    George

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  235. Detect and store business events

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  236. Split system by domains

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  237. View Slide

  238. View Slide

  239. View Slide

  240. Distributed systems

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  241. more here

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  242. Conclusions

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  243. Sometimes event base
    architecture win

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  244. Sometimes not

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  245. EventSourcing is simple as
    conception

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  246. But introduce a lot of practical
    problems

    (data evolution, event order, etc)

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  247. ES expensive

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  248. It’s not about distributed
    systems and communication
    across services

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  249. ES will be a trend in the
    future

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  250. Do you don’t trust?

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  251. ES will be a trend
    in the future

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  252. twitter.com/anton_davydov
    github.com/davydovanton
    [email protected]
    davydovanton.com
    Thank you ❤

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