rails-development

When to Use

• Building or refactoring a Ruby on Rails application.
• Writing ActiveRecord models with validations, associations, and scopes.
• Setting up RESTful routes and controllers following Rails conventions.
• Writing tests with RSpec and FactoryBot.
• Configuring background jobs with Sidekiq or ActiveJob.
• Optimizing database queries to prevent N+1 problems.

Critical Patterns

• Convention Over Configuration: Follow Rails naming conventions strictly. Model User maps to table users, controller UsersController in users_controller.rb. Fighting conventions creates maintenance nightmares.
• Fat Model, Skinny Controller: Controllers handle HTTP flow only — delegate business logic to models, service objects, or concerns.
• Prevent N+1 Queries: ALWAYS use includes, preload, or eager_load when accessing associations in collections. Use bullet gem in development to detect violations.
• Strong Parameters: NEVER trust user input. Whitelist permitted params in every controller action.
• Database-Level Constraints: Add validations in the model AND enforce them at the database level with migration constraints (null: false, unique indexes, foreign keys).
• Background Jobs for Slow Work: Anything over 100ms that isn't the core response (emails, file processing, API calls) goes into a background job.

Code Examples

Model with Validations and Associations

# app/models/user.rb
class User < ApplicationRecord
  # Associations
  has_many :posts, dependent: :destroy
  has_many :comments, through: :posts
  has_one :profile, dependent: :destroy
  belongs_to :organization, optional: true

  # Validations — always mirror with DB constraints
  validates :email, presence: true,
                    uniqueness: { case_sensitive: false },
                    format: { with: URI::MailTo::EMAIL_REGEXP }
  validates :name, presence: true, length: { minimum: 2, maximum: 100 }
  validates :role, inclusion: { in: %w[user admin moderator] }

  # Scopes — chainable, reusable query fragments
  scope :active, -> { where(deactivated_at: nil) }
  scope :admins, -> { where(role: "admin") }
  scope :created_after, ->(date) { where("created_at > ?", date) }
  scope :search, ->(query) {
    where("name ILIKE :q OR email ILIKE :q", q: "%#{sanitize_sql_like(query)}%")
  }

  # Callbacks — use sparingly
  before_save :normalize_email

  private

  def normalize_email
    self.email = email.downcase.strip
  end
end