"Ruby meets Event Sourcing" by Anton Paisov
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The document discusses event sourcing in Ruby, emphasizing its advantages over traditional CRUD operations by improving data auditability and enabling business-oriented development. It presents an implementation example for handling shopping cart item removal using event sourcing and provides resources for further learning. The document highlights the importance of identifying domain state changes and the relevance of event sourcing in legacy applications.
![module EventStoreSetup
def event_store
@event_store ||= RailsEventStore::Client.new.tap do |es|
es.subscribe(Denormalizers::ItemRemovedFromBasket.new,
[Events::ItemRemovedFromBasket])
end
end
end
lib/event_store_setup.rb](https://image.slidesharecdn.com/rubymeetses-160725095953/85/Ruby-meets-Event-Sourcing-by-Anton-Paisov-26-320.jpg)
"Ruby meets Event Sourcing" by Anton Paisov
- 2. Event Sourcing There’s a Person who has an Address We need to change the address
- 3. Event Sourcing There’s a Person who has an Address We need to change the address CRUD: we just remove old one and add a new one
- 4. Event Sourcing There’s a Person who has an Address We need to change the address CRUD: we just remove old one and add a new one ES: publish event about this change and then apply it
- 5. Back to CRUD
- 6. CRUD may hurt business
- 7. CRUD may hurt business Approaching development from business perspective
- 8. CRUD may hurt business Approaching development from business perspective Business avoids updates
- 9. CRUD may hurt business Approaching development from business perspective Business avoids updates Business never deletes
- 10. CRUD may hurt business Approaching development from business perspective Business avoids updates Business never deletes Business loves audit
- 11. What’s the most popular example of ES system among developers?
- 12. GIT!
- 13. +
- 14. Audit
- 15. Debug
- 16. Historic State
- 20. IMPORTANT: Event Sourcing does not mean “must be done ASYNC”
- 21. Also important Can’t do proper ES without identify relevant domain state changes. (from the business point of view) Look for Events that affect domain state and activity.
- 22. Example with implementation Shopping cart Possible to add/remove products from the cart New request: we need to know what was removed
- 25. module Events ItemRemovedFromBasket = Class.new(RailsEventStore::Event) end lib/events.rb
- 26. module EventStoreSetup def event_store @event_store ||= RailsEventStore::Client.new.tap do |es| es.subscribe(Denormalizers::ItemRemovedFromBasket.new, [Events::ItemRemovedFromBasket]) end end end lib/event_store_setup.rb
- 27. app/controllers/orders_controller.rb def remove_item cmd = Command::RemoveItemFromBasket.new(product_params) execute(cmd) head :ok end
- 28. lib/command/remove_item_to_basket.rb module Command class RemoveItemFromBasket < Base attr_accessor :order_id attr_accessor :product_id validates :order_id, presence: true validates :product_id, presence: true alias :aggregate_id :order_id end end
- 30. lib/command_handlers/remove_item_from_basket.rb module CommandHandlers class RemoveItemFromBasket < Command::Handler def call(command) with_aggregate(command.aggregate_id) do |order| order.remove_item(command.product_id) end end private def aggregate_class Domain::Order end end end
- 31. lib/domain/order.rb def remove_item(product_id) apply Events::ItemRemovedFromBasket.new (data: {order_id: id, product_id: product_id}) end def apply_events_item_removed_from_basket(event) order_line.decrease_quantity remove_order_line(order_line) if order_line.empty? end
- 32. lib/denormalizers/item_removed_from_basket.rb module Denormalizers class ItemRemovedFromBasket def call(event) item = find(event.data.order_id, event.data.product_id) item.quantity -= 1 item.quantity > 0 ? item.save! : item.destroy! end ... end end
- 33. On Deck Add Projection usage examples
- 34. Approaches
- 35. Approaches New projects: Event Sourcing
- 36. Approaches New projects: Event Sourcing Legacy: Event Publishing
- 37. Conclusions Help you not to loose data Clean, testable structure with domain events Shines with CQRS May get handy when working on Legacy apps
- 38. Materials Robert Pankowecki about Saga pattern: http://bit.ly/robert-saga
- 39. Materials Great article about ES from business perspective: http://bit.ly/abstract-es Greg Young’s talk recording: http://bit.ly/greg-es Martin Fowler has a lot of content on the topic http://docs.geteventstore.com
- 40. Arkency blogposts on ES and DDD in Ruby http://blog.arkency.com/tags/eventstore/ http://blog.arkency.com/tags/ddd/