rails-idioms

Rails Idioms and Patterns

Rails rewards convention over configuration, Active Record, and RESTful design. Idiomatic Rails = conventional, tested, Hotwire-aware.

Scope: Rails-specific patterns. For Ruby: @.agents/skills/ruby-idioms/SKILL.md.

Active Record

1. Scopes for reusable queries:

   class Task < ApplicationRecord
     scope :active, -> { where(status: :active) }
     scope :by_priority, -> { order(priority: :desc) }
     scope :created_after, ->(date) { where('created_at > ?', date) }
   
     # ✅ Chainable
     # Task.active.by_priority.created_after(1.week.ago)
   end
   

2. Validations in models, not controllers:

   class Task < ApplicationRecord
     validates :title, presence: true, length: { maximum: 200 }
     validates :priority, inclusion: { in: %w[low medium high] }
   
     # ✅ Custom validation
     validate :deadline_must_be_in_future, on: :create
   
     private
   
     def deadline_must_be_in_future
       return unless deadline.present? && deadline < Time.current
       errors.add(:deadline, 'must be in the future')
     end
   end
   

3. includes/preload for eager loading — avoid N+1:

   # ❌ N+1 — fires a query per task to load user
   Task.all.each { |t| puts t.user.name }
   
   # ✅ Eager load — 2 queries total
   Task.includes(:user).each { |t| puts t.user.name }
   
   # ✅ Use Bullet gem to detect N+1 in development
   

4. Callbacks — use sparingly, prefer service objects:

   # ❌ Complex callback chains — hard to test and debug
   before_save :normalize_title, :set_defaults, :notify_assignee
   
   # ✅ Service object — explicit, testable
   class CreateTask
     def call(params)
       task = Task.new(normalize(params))
       task.save!
       NotificationService.notify(task.assignee, task)
       task
     end
   end
   

Controllers

1. RESTful actions — only standard 7 actions per controller. Custom actions = new controller:

   # ❌ Custom action crammed into TasksController
   def complete; end
   
   # ✅ Dedicated controller
   class TaskCompletionsController < ApplicationController
     def create
       task = Task.find(params[:task_id])
       task.complete!
       redirect_to task
     end
   end