Ruby on Rails Basics Cheat Sheet

Covers the Rails CLI, MVC routing and controllers, ActiveRecord models, and core Rails naming conventions for building web apps.

2 PagesBeginnerMar 30, 2026

Rails CLI

Essential commands for scaffolding and running a Rails app.

bash

rails new myapp --database=postgresql   # Create new appcd myapprails generate model Post title:string body:text   # Generate model + migrationrails generate controller Posts index show          # Generate controllerrails db:create                                     # Create databaserails db:migrate                                    # Run migrationsrails server                                        # Start dev server (localhost:3000)rails console                                        # Interactive REPL

Routes & Controllers

Defining RESTful routes and a resourceful controller.

ruby

# config/routes.rbRails.application.routes.draw do  resources :posts            # generates index/show/new/create/edit/update/destroy  root "posts#index"end# app/controllers/posts_controller.rbclass PostsController < ApplicationController  def index    @posts = Post.all  end  def show    @post = Post.find(params[:id])  end  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 post_params    params.require(:post).permit(:title, :body)  endend

Models & ActiveRecord

Associations, validations, and common query methods.

ruby

# app/models/post.rbclass Post < ApplicationRecord  belongs_to :author, class_name: "User"  has_many :comments, dependent: :destroy  validates :title, presence: true, length: { maximum: 100 }end# ActiveRecord query examplesPost.where(published: true).order(created_at: :desc).limit(5)Post.find_by(title: "Hello World")post.comments.create(body: "Nice post!")

MVC Conventions

Naming and structure conventions Rails relies on.

Model naming- Singular, CamelCase class name (Post) mapped to a plural, snake_case table (posts)
Controller naming- Plural, CamelCase class name ending in Controller (PostsController) under app/controllers
Migrations- Timestamped files in db/migrate/, applied in order via rails db:migrate
Convention over configuration- Rails infers foreign keys (post_id), table names, and view paths automatically from class names
Views- app/views/<controller>/<action>.html.erb renders by default, matching the action name
Gemfile / Bundler- Gemfile plus bundle install manage gem dependencies; config/environments/ holds per-environment settings

Pro Tip

Always mass-assign through strong parameters (params.require(:model).permit(...)) in every controller action — skipping it opens the door to mass-assignment vulnerabilities.

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