Vanilla Rails Routing

Routes mirror controller directory structure. Every route points to a controller in the matching namespace.

Resource Extraction (State as Resources)

State changes become singular nested resources, not custom actions:

# Bad - custom actions
resources :cards do
  post :close
  post :archive
end

# Good - state as resource
resources :cards do
  resource :closure, only: [:create, :destroy]
  resource :archival, only: [:create, :destroy]
end

resource (singular) = one state per parent. create = enter state. destroy = leave state.

Controller Directory Mapping

Route nesting mirrors app/controllers/ directory:

# routes.rb
resources :boards do
  resources :cards do
    resource :closure
  end
end

# Maps to:
# app/controllers/boards_controller.rb
# app/controllers/boards/cards_controller.rb
# app/controllers/boards/cards/closures_controller.rb

Rule: If a route is nested under boards, the controller lives in boards/ directory.

Shallow Nesting

Avoid deeply nested URLs. Use shallow: or flatten when resource has its own identity:

# Deep (avoid for >2 levels)
/boards/1/cards/2/comments/3/reactions/4

# Shallow
resources :boards do
  resources :cards, shallow: true
end
# Produces:
# /boards/:board_id/cards     (index, new, create)
# /cards/:id                  (show, edit, update, destroy)

Rule: If you can look up the resource by its own ID, it doesn't need parent in URL.

Module Scoping

Group related controllers under modules for admin/API/etc:

namespace :admin do
  resources :accounts    # Admin::AccountsController
end

scope module: :api do
  resources :cards       # Api::CardsController (no /api prefix in URL)
end

scope "/api" do
  resources :cards       # CardsController (with /api prefix, no module)
end

Resolve Helpers

Use resolve to control polymorphic URL generation:

# Without resolve: url_for(@card) might generate wrong path
resolve("Card") { |card| [card.board, card] }

# Now polymorphic_path(@card) generates /boards/:board_id/cards/:id

Use when polymorphic routing needs explicit parent context.

Direct Routes

Name custom routes for URL helpers:

direct(:homepage) { "/" }
direct(:dashboard) { |account| "/#{account.to_param}/dashboard" }

# Usage: homepage_url, dashboard_url(@account)

Quick Reference

Red Flags

• Custom member/collection actions for state changes → extract resource
• Controller file not matching route nesting → move controller
• 3+ levels of URL nesting → use shallow: or flatten
• url_for generating wrong paths → add resolve
• Route with no corresponding controller directory → create directory