Rails Expert Skill for Claude

Rails Expert

Core Workflow

• Analyze requirements — Identify models, routes, real-time needs, background jobs
• Scaffold resources — rails generate model User name:string email:string, rails generate controller Users
• Run migrations — rails db:migrate and verify schema with rails db:schema:dump
• If migration fails: inspect db/schema.rb for conflicts, rollback with rails db:rollback, fix and retry
• Implement — Write controllers, models, add Hotwire (see Reference Guide below)
• Validate — bundle exec rspec must pass; bundle exec rubocop for style
• If specs fail: check error output, fix failing examples, re-run with --format documentation for detail
• If N+1 queries surface during review: add includes/eager_load (see Common Patterns) and re-run specs
• Optimize — Audit for N+1 queries, add missing indexes, add caching

Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |

|-------|-----------|-----------|

| Hotwire/Turbo | references/hotwire-turbo.md | Turbo Frames, Streams, Stimulus controllers |

| Active Record | references/active-record.md | Models, associations, queries, performance |

| Background Jobs | references/background-jobs.md | Sidekiq, job design, queues, error handling |

| Testing | references/rspec-testing.md | Model/request/system specs, factories |

| API Development | references/api-development.md | API-only mode, serialization, authentication |

Common Patterns

N+1 Prevention with includes/eager_load

# BAD — triggers N+1
posts = Post.all
posts.each { |post| puts post.author.name }

# GOOD — eager load association
posts = Post.includes(:author).all
posts.each { |post| puts post.author.name }

# GOOD — eager_load forces a JOIN (useful when filtering on association)
posts = Post.eager_load(:author).where(authors: { verified: true })

Turbo Frame Setup (partial page update)

<%# app/views/posts/index.html.erb %>
<%= turbo_frame_tag "posts" do %>
  <%= render @posts %>
  <%= link_to "Load More", posts_path(page: @next_page) %>
<% end %>

<%# app/views/posts/_post.html.erb %>
<%= turbo_frame_tag dom_id(post) do %>
  <h2><%= post.title %></h2>
  <%= link_to "Edit", edit_post_path(post) %>
<% end %>

# app/controllers/posts_controller.rb
def index
  @posts = Post.includes(:author).page(params[:page])
  @next_page = @posts.next_page
end

Sidekiq Worker Template

# app/jobs/send_welcome_email_job.rb
class SendWelcomeEmailJob < ApplicationJob
  queue_as :default
  sidekiq_options retry: 3, dead: false

  def perform(user_id)
    user = User.find(user_id)
    UserMailer.welcome(user).deliver_now
  rescue ActiveRecord::RecordNotFound => e
    Rails.logger.warn("SendWelcomeEmailJob: user #{user_id} not found — #{e.message}")
    # Do not re-raise; record is gone, no point retrying
  end
end

# Enqueue from controller or model callback
SendWelcomeEmailJob.perform_later(user.id)

Strong Parameters (controller template)

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  before_action :set_post, only: %i[show edit update destroy]

  def create
    @post = Post.new(post_params)
    if @post.save
      redirect_to @post, notice: "Post created."
    else
      render :new, status: :unprocessable_entity
    end
  end

  private

  def set_post
    @post = Post.find(params[:id])
  end

  def post_params
    params.require(:post).permit(:title, :body, :published_at)
  end
end

Constraints

MUST DO

• Prevent N+1 queries with includes/eager_load on every collection query involving associations
• Write comprehensive specs targeting >95% coverage
• Use service objects for complex business logic; keep controllers thin
• Add database indexes for every column used in WHERE, ORDER BY, or JOIN
• Offload slow operations to Sidekiq — never run them synchronously in a request cycle

MUST NOT DO

• Skip migrations for schema changes
• Use raw SQL without sanitization (sanitize_sql or parameterized queries only)
• Expose internal IDs in URLs without consideration

Output Templates

When implementing Rails features, provide:

• Migration file (if schema changes needed)
• Model file with associations and validations
• Controller with RESTful actions and strong parameters
• View files or Hotwire setup
• Spec files for models and requests
• Brief explanation of architectural decisions

Documentation