Rails Expert

Rails Expert Skill

This skill provides deep Rails expertise including ActiveRecord optimization, architectural patterns, security best practices, Hotwire integration, and testing strategies.

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🔥 Common Pitfalls

N+1 Query Problem

# ❌ N+1 — 1 + N queries
Post.all.each do |post|
  puts post.author.name
end

# ✅ Eager loading — 2 queries
Post.includes(:author).each do |post|
  puts post.author.name
end

# ✅ Nested eager loading
Post.includes(author: :profile, comments: :user).all

# ✅ Preload vs Includes vs Eager_load
Post.preload(:author)     # Separate query
Post.includes(:author)    # Smart (preload or eager_load)
Post.eager_load(:author)  # LEFT OUTER JOIN

Mass Assignment

# ❌ Dangerous - permits everything
params.permit!

# ❌ Sensitive fields
params.require(:user).permit(:name, :email, :admin)

# ✅ Safe - explicit whitelist
params.require(:user).permit(:name, :email, :bio)

# ✅ Admin fields with explicit check
if current_user.admin?
  params.require(:user).permit(:name, :email, :admin)
else
  params.require(:user).permit(:name, :email)
end

Callbacks Gotchas

# ❌ Side effects in callbacks
class User < ApplicationRecord
  after_create :send_welcome_email  # Hard to test, implicit
end

# ✅ Explicit in controller/service
class UsersController < ApplicationController
  def create
    @user = User.create!(user_params)
    UserMailer.welcome(@user).deliver_later
  end
end

# When callbacks ARE appropriate:
# - Data normalization (before_validation)
# - Timestamps
# - Counter cache updates

---

🏗️ Architecture Patterns

Service Objects (POROs)

# app/services/users/create_user.rb
module Users
  class CreateUser
    def initialize(params, current_user: nil)
      @params = params
      @current_user = current_user
    end

    def call
      user = User.new(@params)

      ActiveRecord::Base.transaction do
        user.save!
        create_profile(user)
        enqueue_welcome_email(user)
      end

      Result.new(success: true, user: user)
    rescue ActiveRecord::RecordInvalid => e
      Result.new(success: false, errors: e.record.errors)
    end

    private

    def create_profile(user)
      Profile.create!(user: user)
    end

    def enqueue_welcome_email(user)
      UserMailer.welcome(user).deliver_later
    end
  end
end

# Usage
result = Users::CreateUser.new(user_params).call
if result.success?
  redirect_to result.user
else
  render :new, status: :unprocessable_entity
end