ruby-expert

name	ruby-expert
version	1.0.0
description	Expert-level Ruby development with Rails, modern features, testing, and best practices
category	languages
tags	["ruby","rails","rspec","gem","sinatra","metaprogramming"]
allowed-tools	["Read","Write","Edit","Bash(ruby:*, gem:*, bundle:*, rails:*)"]

Ruby Expert

Expert guidance for Ruby development, including Ruby 3+ features, Rails framework, testing with RSpec, and Ruby best practices.

Core Concepts

Ruby 3+ Features

• Pattern matching
• Ractors (parallel execution)
• Fibers (cooperative concurrency)
• Type signatures (RBS)
• Endless methods
• Numbered block parameters
• Hash literal value omission

Object-Oriented

• Everything is an object
• Classes and modules
• Inheritance and mixins
• Method visibility (public, private, protected)
• Singleton methods and eigenclasses
• Duck typing

Functional Features

• Blocks, procs, and lambdas
• Higher-order functions (map, reduce, select)
• Enumerables
• Lazy evaluation

Modern Ruby Syntax

Pattern Matching (Ruby 3.0+)

# Case/in pattern matching
def process_response(response)
  case response
  in { status: 200, body: }
    puts "Success: #{body}"
  in { status: 404 }
    puts "Not found"
  in { status: 500..599, error: message }
    puts "Server error: #{message}"
  else
    puts "Unknown response"
  end
end

# Rightward assignment
response = { status: 200, body: "OK" }
response => { status:, body: }
puts status  # 200
puts body    # "OK"

# Array pattern matching
def summarize(data)
  case data
  in []
    "Empty"
  in [item]
    "Single item: #{item}"
  in [first, *rest]
    "First: #{first}, Rest: #{rest.length} items"
  end
end

Endless Methods

# Single-line method definition
def greet(name) = "Hello, #{name}!"

def square(x) = x * x

def full_name = "#{first_name} #{last_name}"

class User
  attr_reader :name, :email

  def initialize(name:, email:) = (@name = name; @email = email)

  def admin? = @role == :admin
end

Numbered Block Parameters

# Use _1, _2, etc. for block parameters
[1, 2, 3].map { _1 * 2 }  # [2, 4, 6]

{ a: 1, b: 2 }.map { "#{_1}: #{_2}" }  # ["a: 1", "b: 2"]

users.sort_by { [_1.last_name, _1.first_name] }

Hash Literal Value Omission

name = "Alice"
age = 30
email = "[e-mail]"

# Before
user = { name: name, age: age, email: email }

# After (Ruby 3.1+)
user = { name:, age:, email: }

Ruby on Rails

Rails 7+ Application

# app/models/user.rb
class User < ApplicationRecord
  # Validations
  validates :email, presence: true, uniqueness: true, format: { with: URI::MailTo::EMAIL_REGEXP }
  validates :name, presence: true, length: { minimum: 2, maximum: 100 }
  validates :age, numericality: { greater_than_or_equal_to: 18 }, allow_nil: true

  # Associations
  has_many :posts, dependent: :destroy
  has_many :comments, dependent: :destroy
  has_many :likes, dependent: :destroy
  has_many :liked_posts, through: :likes, source: :post

  # Scopes
  scope :active, -> { where(active: true) }
  scope :recent, -> { order(created_at: :desc) }
  scope , -> { joins().distinct }

  
  before_save 
  after_create 

  
  enum  {  ,  ,   }

  
   
    
  

   
    role == 
  

  

   
    .email = email.downcase.strip
  

   
    .welcome().deliver_later
  



  < 
  belongs_to 
  has_many ,  
  has_many ,  
  has_many ,  ,  

  has_one_attached 
  has_rich_text 

  validates ,  ,  {  ,   }
  validates ,  

  scope , -> { where( ) }
  scope , ->(user) { where( user) }
  scope , ->(query) { where(, , ) }

  before_save 

   
    update!( ,  .current)
  

  

   
    .slug = title.parameterize
  

Controllers

# app/controllers/api/v1/posts_controller.rb
module Api
  module V1
    class PostsController < ApplicationController
      before_action :authenticate_user!, except: [:index, :show]
      before_action :set_post, only: [:show, :update, :destroy]
      before_action :authorize_post, only: [:update, :destroy]

      # GET /api/v1/posts
      def index
        @posts = Post.published
                     .includes(:user, :comments)
                     .page(params[:page])
                     .per(20)

        render json: @posts, each_serializer: PostSerializer
      end

      # GET /api/v1/posts/:id
      def show
        render json: @post, serializer: PostSerializer, include: [:user, :comments]
      end

      # POST /api/v1/posts
      def create
         = current_user.posts.build(post_params)

         .save
          render  ,  ,  
        
          render  {  .errors.full_messages },  
        
      

      
       
         .update(post_params)
          render  ,  
        
          render  {  .errors.full_messages },  
        
      

      
       
        .destroy
        head 
      

      

       
         = .find(params[])
       
        render  {   },  
      

       
         .user == current_user || current_user.admin?
          render  {   },  
        
      

       
        params.().permit(, , , )
      
    
  

Active Record Queries

# Efficient queries
User.includes(:posts).where(posts: { published: true })
User.joins(:posts).group('users.id').having('COUNT(posts.id) > ?', 5)
User.left_joins(:posts).where(posts: { id: nil })  # Users with no posts

# Complex queries
Post.where('created_at > ?', 1.week.ago)
    .where(published: true)
    .order(created_at: :desc)
    .limit(10)

# Find or create
user = User.find_or_create_by(email: '[e-mail]') do |u|
  u.name = 'New User'
  u.role = :user
end

# Upsert (Rails 6+)
User.upsert({ email: '[e-mail]', name: 'Alice' }, unique_by: :email)

# Batch processing
User.find_each(batch_size: 100) do |user|
  user.update_subscription_status
end

# Transactions
ActiveRecord.transaction 
  user.update!( user.balance - amount)
  recipient.update!( recipient.balance + amount)
  .create!( user,  recipient,  amount)



.connection.execute(
  
)

Background Jobs (Sidekiq)

# app/jobs/send_email_job.rb
class SendEmailJob < ApplicationJob
  queue_as :default
  retry_on Net::SMTPServerBusy, wait: :exponentially_longer

  def perform(user_id, email_type)
    user = User.find(user_id)
    case email_type
    when 'welcome'
      UserMailer.welcome(user).deliver_now
    when 'notification'
      UserMailer.notification(user).deliver_now
    end
  end
end

# Usage
SendEmailJob.perform_later(user.id, 'welcome')
SendEmailJob.set(wait: 1.hour).perform_later(user.id, 'notification')

Mailers

# app/mailers/user_mailer.rb
class UserMailer < ApplicationMailer
  default from: '[e-mail]'

  def welcome(user)
    @user = user
    @url  = 'https://example.com/login'
    mail(to: @user.email, subject: 'Welcome to My App')
  end

  def notification(user, message)
    @user = user
    @message = message
    mail(
      to: @user.email,
      subject: 'New Notification',
      reply_to: '[e-mail]'
    )
  end
end

Routes

# config/routes.rb
Rails.application.routes.draw do
  root 'home#index'

  # RESTful resources
  resources :posts do
    member do
      post :publish
      post :like
    end
    collection do
      get :trending
    end
    resources :comments, only: [:create, :destroy]
  end

  # Nested resources
  resources :users do
    resources :posts, only: [:index, :show]
  end

  # Namespaced routes
  namespace :api do
    namespace :v1 do
      resources :posts, only: [:index, :show, :create, :update, :destroy]
      resources :users, only: [:index, :show]
    end
  end

  # Constraints
  constraints(subdomain: 'api') do
    scope module: 'api' do
      resources :posts
    
  

  
  get ,  
  post ,  

Testing with RSpec

Model Specs

# spec/models/user_spec.rb
require 'rails_helper'

RSpec.describe User, type: :model do
  describe 'validations' do
    it { should validate_presence_of(:email) }
    it { should validate_uniqueness_of(:email) }
    it { should validate_presence_of(:name) }
    it { should validate_length_of(:name).is_at_least(2).is_at_most(100) }
  end

  describe 'associations' do
    it { should have_many(:posts).dependent(:destroy) }
    it { should have_many(:comments).dependent(:destroy) }
  end

  describe '#full_name' do
    it 'returns the full name' do
      user = User.new(first_name: 'Alice', last_name: 'Smith')
      expect(user.full_name).to eq('Alice Smith')
    end
  end

  describe '#admin?' do
    it 'returns true for admin users' do
      user = User.new(role: :admin)
      expect(user).to be_admin
    end

    it 'returns false for regular users' do
      user = User.new(role: )
      expect(user).not_to be_admin
    
  

  describe  
    it  
      user = create(,  )
      expect(user.email).to eq()
    

    it  
      expect {
        create()
      }.to have_enqueued_job().with(anything, )
    
  

Controller Specs

# spec/controllers/posts_controller_spec.rb
require 'rails_helper'

RSpec.describe PostsController, type: :controller do
  let(:user) { create(:user) }
  let(:post) { create(:post, user: user) }

  describe 'GET #index' do
    it 'returns a success response' do
      get :index
      expect(response).to have_http_status(:success)
    end

    it 'assigns @posts' do
      post1 = create(:post, published: true)
      post2 = create(:post, published: true)
      get :index
      expect(assigns(:posts)).to match_array([post1, post2])
    end
  end

  describe 'POST #create' do
    context 'when authenticated' do
      before { sign_in user }

      context 'with valid params' do
        let(:valid_params) { { post: { title: 'Test Post', content: 'Content' } } }

        it 'creates a new post' do
          expect {
            post :create, params: valid_params
          }.to change(, ).by()
        

        it  
          post ,  valid_params
          expect(response).to have_http_status()
        
      

      context  
        let() { {  {   } } }

        it  
          expect {
            post ,  invalid_params
          }.not_to change(, )
        

        it  
          post ,  invalid_params
          expect(response).to have_http_status()
        
      
    

    context  
      it  
        post ,  {  {   } }
        expect(response).to have_http_status()
      
    
  

Request Specs

# spec/requests/api/v1/posts_spec.rb
require 'rails_helper'

RSpec.describe 'Api::V1::Posts', type: :request do
  let(:user) { create(:user) }
  let(:headers) { { 'Authorization' => "Bearer #{user.auth_token}" } }

  describe 'GET /api/v1/posts' do
    before do
      create_list(:post, 3, published: true)
      create(:post, published: false)
    end

    it 'returns published posts' do
      get '/api/v1/posts'
      expect(response).to have_http_status(:success)
      expect(JSON.parse(response.body).length).to eq(3)
    end

    it 'paginates results' do
      create_list(:post, 25, published: true)
      get '/api/v1/posts', params: { page: 2 }
      expect(JSON.parse(response.body).length).to eq(8)  # 28 total, 20 per page
    end
  end

  describe 'POST /api/v1/posts' do
    context 'with valid params' 
      let() 
        {  {  ,   } }
      

      it  
        expect {
          post ,  valid_params,  headers
        }.to change(, ).by()
      

      it  
        post ,  valid_params,  headers
        expect(response).to have_http_status()
        expect(.parse(response.body)[]).to eq()
      
    
  

FactoryBot

# spec/factories/users.rb
FactoryBot.define do
  factory :user do
    sequence(:email) { |n| "user#{n}@example.com" }
    name { Faker::Name.name }
    password { 'password123' }
    role { :user }

    trait :admin do
      role { :admin }
    end

    trait :with_posts do
      transient do
        posts_count { 5 }
      end

      after(:create) do |user, evaluator|
        create_list(:post, evaluator.posts_count, user: user)
      end
    end
  end

  factory :post do
    association :user
    title { Faker::Lorem.sentence }
    content { Faker::Lorem.paragraph }
    published { false }

    trait :published do
      published { true }
      published_at { Time.current }
    end
  end
end

# Usage
user = create(:user)
admin = create(:user, )
user_with_posts = create(, ,  )
published_post = create(, )

Metaprogramming

# Define methods dynamically
class User
  %w[name email phone].each do |attr|
    define_method("#{attr}_present?") do
      send(attr).present?
    end
  end
end

# Method missing
class Configuration
  def initialize
    @settings = {}
  end

  def method_missing(method, *args)
    method_name = method.to_s
    if method_name.end_with?('=')
      @settings[method_name.chomp('=')] = args.first
    else
      @settings[method_name]
    end
  end

  def respond_to_missing?(method, include_private = false)
    true
  end
end

config = Configuration.new
config.api_key = 'secret'
config.api_key  # => 'secret'

# Class macros
module Timestampable
  def self.included(base)
    base.extend(ClassMethods)
  end

  module 
     
      before_save 

      () 
        .updated_at = .current
        .created_at ||= .current
      
    
  


 
   
  timestampable

Best Practices

Code Style

• Follow Ruby Style Guide
• Use 2-space indentation
• Prefer symbols over strings for keys
• Use snake_case for methods and variables
• Use CamelCase for classes
• Use meaningful variable names

Performance

• Use includes to avoid N+1 queries
• Add database indexes on foreign keys
• Use select to load only needed columns
• Use find_each for large datasets
• Cache expensive computations

Security

• Use strong parameters in controllers
• Sanitize user input
• Protect against SQL injection (use parameterized queries)
• Use CSRF protection
• Implement authentication and authorization
• Keep dependencies updated

Anti-Patterns to Avoid

❌ Fat models: Extract logic to service objects ❌ N+1 queries: Use includes or eager_load ❌ Long controller actions: Extract to services ❌ Missing indexes: Add indexes on foreign keys ❌ Skipping validations: Always validate data ❌ Exposing internals: Use serializers for API responses ❌ Global state: Avoid global variables and class variables

Resources

• Ruby Documentation: https://ruby-doc.org/
• Rails Guides: https://guides.rubyonrails.org/
• RSpec: https://rspec.info/
• Ruby Style Guide: https://rubystyle.guide/
• Rails API: https://api.rubyonrails.org/