Introduction to Rails

The framework that made Ruby famous.

Introduction to Rails

Ruby on Rails is the web framework that made Ruby famous. Created by David Heinemeier Hansson in 2004, Rails follows convention over configuration — you write less code because sensible defaults handle the details. It's MVC, it's RESTful, and it's incredibly productive.

# Create a new Rails app
# rails new myapp

# Generate a scaffold
# rails generate scaffold Post title:string body:text

# Run migrations
# rails db:migrate

# Start the server
# rails server

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Convention Over Configuration

Rails makes assumptions instead of requiring configuration. If your model is called User, Rails assumes it maps to a users table with columns named after the model's attributes. You don't write XML configs or boilerplate — you just follow the conventions.

# Rails conventions:
# Model:      User       -> users table
# Controller: UsersController -> app/controllers/users_controller.rb
# View:       index.html.erb -> app/views/users/index.html.erb
# Route:      /users     -> UsersController#index

# No config needed for:
# - Database connection (config/database.yml)
# - Routing (config/routes.rb)
# - View templates (app/views/)

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MVC Pattern

Rails follows Model-View-Controller. Models handle data and business logic. Views handle presentation. Controllers connect them. This separation keeps code organized and maintainable.

# app/models/post.rb
class Post < ApplicationRecord
  validates :title, presence: true
  validates :body, presence: true

  scope :published, -> { where(published: true) }
end

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def index
    @posts = Post.published
  end

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

# app/views/posts/index.html.erb
# <% @posts.each do |post| %>
#   <h2><%= post.title %></h2>
#   <p><%= post.body %></p>
# <% end %>

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ActiveRecord

ActiveRecord is Rails' ORM (Object-Relational Mapping). It maps Ruby objects to database tables. You interact with your database using Ruby methods instead of SQL. It handles validations, callbacks, associations, and queries.

# Define a model
class User < ApplicationRecord
  has_many :posts
  has_one :profile

  validates :email, presence: true, uniqueness: true
  validates :name, length: { minimum: 2 }
end

# Use it in code
user = User.create(name: "Alice", email: "alice@example.com")
user.posts.create(title: "Hello World")

# Query with friendly methods
User.where(name: "Alice").first
User.order(:created_at).limit(10)
User.joins(:posts).where(posts: { published: true })

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Why Rails Made Ruby Famous

Rails showed the world that web development could be fast and enjoyable. It introduced concepts like RESTful routing, database migrations, and scaffolding that became industry standards. Rails is opinionated but productive — it makes decisions so you don't have to. That's why startups and enterprises alike chose Rails.

# config/routes.rb
Rails.application.routes.draw do
  resources :posts do
    member do
      post :publish
    end
    collection do
      get :drafts
    end
  end

  root "posts#index"
end

# This single file generates:
# GET    /posts          -> index
# GET    /posts/new      -> new
# POST   /posts          -> create
# GET    /posts/:id      -> show
# GET    /posts/:id/edit -> edit
# PATCH  /posts/:id      -> update
# DELETE /posts/:id      -> destroy
# POST   /posts/:id/publish -> publish
# GET    /posts/drafts   -> drafts

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🧪 Quick Quiz

What pattern does Rails follow?

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