From Rails legacy to DDD - Pivorak, Lviv
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Rails is optimised for the first weeks of development. At the later phases it's no longer the speed of adding new views and data that matters. It's often more about the different (and changing!) ways of using the data. The business logic gets more complicated. DDD has answers to those problems. Detecting the bounded contexts is the crucial skill. Choose which parts of the app leave as CRUD and which could go into more of the tactical DDD.
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From Rails legacy to DDD - Pivorak, Lviv
- 2. Agenda • What is legacy • Why and when Rails becomes legacy • What is DDD • Why it’s worth learning • How to gradually go DDD - lessons learnt
- 3. Andrzej Krzywda • 11 years with Rails • running Arkency (Ruby agency) • writing Ruby-related books • RailsRefactoring.com • blogging • teaching Rails at University of Wroclaw (for the last 5 years) • organising wroc_love.rb • DRUG meetups in Wrocław
- 4. Andrzej Krzywda • reviewed hundreds of Rails apps • helped several Rails teams • dealing with bigger Rails apps
- 5. What is legacy code?
- 6. Legacy • Frameworks • monolithic • no architecture • no tests
- 7. • “code written yesterday” • “code written by someone else” • “not my code” • “not in my favourite architecture”
- 8. How do Rails apps become legacy?
- 9. Rails is optimised for the first weeks of development
- 10. Bringing us joy and speed
- 11. Optimised for adding new forms/tables/ columns
- 12. Not optimised for complex business logic
- 15. • slow tests • the test setup is long and complicated • critical bugs more often • slower development progress • conflicts in the team, related to the code • complicated codebase • infinite API
- 17. DDD aims to help with complex business logic
- 18. Most popular in .NET and Java, but also strong in the PHP community
- 19. Why is DDD not popular in the Rails community?
- 20. Mostly due to our Java-hate DNA
- 21. Why it’s worth learning DDD?
- 22. • New techniques • new tools • Solutions to complicated business logic • solutions in non-Ruby worlds • shared language with other programmers • microservices!
- 23. How to start?
- 24. Service objects are the gateway drug
- 26. Tactical DDD • entity • value objects • aggregate • domain event • services • repositories • factory
- 27. DDD-lite • app service • calls 1 or more domain services • domain service • takes repo as input • load aggregate from the repo • do sth cool • may use some value objects • may trigger some domain events • save aggregate (repo)
- 28. • URL • Rails action • App service • Domain service • Repo • ActiveRecord • Database
- 29. One app service can call multiple domain services
- 30. UpdateCustomer == MoveToNewAddress ChangeEmail IntroduceNewContactPerson In one of our projects one request was about 15 domain services “Update” is always hiding a lot
- 32. Strategic DDD • bounded contexts • context map
- 33. Warning: next slide is almost like UML
- 36. optionally as microservices partially available different persistence data duplication Context Map HR Project Management Finances Invoicing CRUD DDD-lite external SaaS Communication developer project client DDD-lite
- 37. bounded contexts as namespaces in Ruby
- 38. How to get there from legacy? BTW, There’s no such thing as the ultimate DDD codebase
- 39. Draw the Context Map aka what are the boxes in your application aka you have more apps They are potential microservices
- 40. Decide which contexts are CRUD and which ones need more logic (DDD-lite) the ones with CRUD ideally need to publish events anyway
- 41. Bounded contexts • Inventory • Invoicing • Ordering • Finances • Forum
- 42. Ongoing process No time for 2-months rewrites
- 44. Escape from the CRUD verbs Talk more to the business people
- 46. Test coverage #noregressions when you’re a client you don’t like them too
- 47. Line coverage* is a joke *rcov, simplecov
- 48. Mutation testing is the real test coverage! http://blog.arkency.com/2015/04/why-i-want-to-introduce-mutation-testing-to-the-rails-event-store-gem/ http://blog.arkency.com/2015/06/how-good-are-your-ruby-tests-testing-your-tests-with-mutant/
- 49. You want to try mutant (today)
- 50. mutant == testing your tests == refactoring with confidence
- 51. Test units, not classes! http://andrzejonsoftware.blogspot.com/2015/02/tdding-unit-not-class.html http://andrzejonsoftware.blogspot.com/2014/04/tdd-and-rails-what-makes-good-unit.html http://blog.arkency.com/2014/09/unit-tests-vs-class-tests/
- 52. Escape from the framework ASAP http://blog.arkency.com/2015/03/extract-a-service-object-in-any-framework/ Call application services from the framework let Rails deal only with HTTP
- 53. Don’t just pass the params/hash everywhere http://andrzejonsoftware.blogspot.com/2011/12/args-opts-params.html
- 54. Wrap your legacy contexts with the application services layer
- 55. Use events to communicate between bounded contexts rails_event_store https://github.com/arkency/rails_event_store
- 56. Sync may be safer than async
- 57. Separate reads/writes at the services layer CQRS
- 58. Eliminate querying from BC to another Push the data!
- 59. Keep the Bounded Contexts in-sync by publishing all the important events
- 60. Easier testing when no dependency on other system
- 62. When in doubt, think in aggregates
- 64. Event sourcing build your aggregates from events audit log for free
- 66. Easier setup of the project when it’s a smaller piece Useful when you’re maintaining many projects and need to bugfix them from time to time
- 67. Legacy -> DDD books • red book, Vaughn Vernon • Implementing DDD • blue book, Eric Evans • Refactoring, Fowler • Legacy code, Feathers
- 68. THANKS!