mini-rails_KaigiOnRails2026_EN.pdf

Kaigi on Rails2026 の登壇資料です。
https://kaigionrails.org/2026/talks/Hitoshi-Noborikawa/

Transcript

1. Understanding How Rails Works by Building It Small 〜 mini-rails 〜 1
2. Nobo I work at SonicGarden Inc. I organize Seto.rb. Also organizing 沖縄Ruby会議03 !（Feb 20 2027） @Hitoshi-Noborikawa 2
3. How It Started 3
4. The more I used Rails every day, the more I wondered what was happening inside. What is Rails.application.routes.draw? What does where actually do? When is a view loaded? I know — let's read the Rails source. 4
5. I tried to look up the definition of where, but... So many methods I didn't understand: include, extend, included, define_method... Too early for me. Time to come back later. 5
6. Expanding what I could read, bit by bit Metaprogramming Reading the source code of small gems Reading the code of projects I work on, closely Maybe I can do it now? 6
7. Reading got easier, but Rails is still too big I understand the parts, but not the whole picture What if I build a small one to see the whole picture? 7
8. mini-rails 8
9. About mini-rails A framework I built myself, modeled mainly on Rails 1–3. Strictly a learning project. I'll publish it on GitHub after this talk. 9
10. What This Talk Covers Walking through Request → Response with a mini blog running on mini-rails. The focus is on the mini-rails implementation. 10
11. Demo 11
13. Mapping to Rails mini-rails Rails MiniPack ActionPack MiniRecord ActiveRecord MiniView ActionView MiniModel ActiveModel MiniSupport ActiveSupport 13
14. Start Rack → Router → Controller → View → Response 14
15. Rack Rack → Router → Controller → View → Response 15
16. rackup → run MiniRails.application Rails: the Application sits on top of a middleware stack mini-rails: only the bare minimum middleware Reference: railties/lib/rails/application.rb 16
17. Just calls routes.call(env) 17
18. Router Rack → Router → Controller → View → Response 18
19. draw → resources There's a Mapper class in between — skipping it here 19
20. Defines each action Kept simple on purpose. Rails is far more complex Reference: actionpack/lib/action_dispatch/routing/mapper.rb 20
21. Stores routes in an array Calls add_route 21
22. Finds the route, hands off to the controller GET /posts matches posts#index; dispatch hands off to the controller 22
23. Controller Rack → Router → Controller → View → Response 23
24. Finds PostsController, calls dispatch 24
25. process calls the action 25
26. Calls the action with public_send 26
27. MiniRecord Rack → Router → Controller (MiniRecord) → View → Response 27
28. Post.order 28
29. Post.order goes through all Rails: delegate(*QUERYING_METHODS, to: :all) No delegate here — order, where and find all go through define_method Reference: activerecord/lib/active_record/querying.rb 29
30. all creates a new Relation If it were reused, A's conditions would leak into B Rails: all is current_scope || default_scoped — default_scope and scoping feed in mini-rails: just returns a new Relation 30
31. Stacks up the Relation 31
32. Builds the SQL Rails: builds an Arel AST, and a Visitor turns it into SQL mini-rails: just concatenates strings 32
33. @post.save 33
34. save create_record is called for a new record valid? runs validations and run_callbacks runs before/after callbacks, but I'll skip those here 34
35. create_record 35
36. View Rack → Router → Controller → View → Response 36
37. Renders the view Rails splits this into Callbacks and ImplicitRender; mini-rails has only this method Reference: actionpack/lib/action_controller/metal/implicit_render.rb 37
38. Calls the Renderer 38
39. Reads the template, passes it to ERB Rails: caches templates mini-rails: reads them on every request Reference: actionview/lib/action_view/template.rb 39
40. The action's HTML is a block; the layout's yield calls it 40
41. Response Rack → Router → Controller → View → Response Rails: returns it via Response#to_a mini-rails: named to_rack_response for clarity Reference: actionpack/lib/action_dispatch/http/response.rb 41
42. Finish 🎉🎉 Rack → Router → Controller → View → Response 42
43. Other Features 43
44. Post works without any require Autoloaded at boot Rails: Zeitwerk also uses Ruby's autoload, and reloads on change mini-rails: same idea, once at boot — no reloading 44
45. before_action Appended to an array when the class loads, then run per request via only / except Rails: AbstractController::Callbacks, which also controls conditions and execution order mini-rails: just runs an array of hashes 45
46. Features I Couldn't Cover - MiniSupport::Concern - Migration - Validation - HashWithIndifferentAccess - MiniPack::Flash - MiniView::Helpers - MiniView::Partial 46
47. What to Do After This Talk Read mini-rails Next read the Rails 1.x implementation https://github.com/Hitoshi-Noborikawa/mini-rails 47
48. Thank you! 48