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Ruby on Rails

Ruby on Rails cheat sheet with MVC architecture, Active Record, routing, migrations, controllers, and deployment code examples.

8 min read
railsrubymvcactive-recordbackendweb-frameworkgeneratorsmigrations

Getting Started

New Rails Application

Create a new Rails application with various options

bash
✅ Default database is SQLite, use --database for PostgreSQL/MySQL
💡 --api flag creates lightweight API-only app
🔍 --skip-test useful if using RSpec instead of Minitest
⚡ Use rails new --help to see all available options
setupclinew-app

Rails Server & Console

Start development server and interactive console

bash
✅ Default server runs on localhost:3000
💡 Use rails c --sandbox to test without affecting database
🔍 reload! in console reloads code without restarting
⚡ rails server accepts same flags as rails s
serverconsoledevelopment

Generators

Model Generator

Generate models with migrations and attributes

bash
✅ Automatically creates migration, model, and test files
💡 Use references for associations (creates foreign key)
🔍 :index adds database index, :uniq adds unique index
⚡ rails destroy model reverses the generator
generatormodelmigration

Controller Generator

Generate controllers with actions and views

bash
✅ Creates controller, views, helper, and routes
💡 --skip-template-engine for API-only controllers
🔍 Namespaced controllers use slashes: api/v1/Users
⚡ Actions listed after controller name become methods
generatorcontrollercrud

Scaffold Generator

Generate complete CRUD resource with all components

bash
✅ Creates model, migration, controller, views, routes, tests
💡 Great for prototyping, customize afterwards
🔍 --api flag creates API-only scaffold without views
⚠️ Generates a lot of files - review before committing
generatorscaffoldcrudfull-stack

Migration Generator

Generate standalone database migrations

bash
✅ Rails infers migration content from name convention
💡 AddXxxToYyy and RemoveXxxFromYyy auto-generate code
🔍 Use CreateJoinTable for many-to-many relationships
⚡ Always review generated migration before running
generatormigrationdatabase

Database & Migrations

Database Commands

Create, migrate, and manage database

bash
✅ db:create creates database defined in database.yml
💡 db:reset drops and recreates from schema.rb
🔍 db:setup is for first-time setup, db:reset for refresh
⚡ Always backup production before db:reset or db:drop
databasemigrationssetup

Migration Methods

Common methods used in migration files

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✅ t.timestamps adds created_at and updated_at
💡 Use references for foreign keys with index
🔍 precision and scale control decimal places
⚡ Add indexes for frequently queried columns
migrationsschemadatabase

Routes

Resourceful Routes

RESTful routes with resources

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✅ resources generates 7 RESTful routes automatically
💡 Use only/except to limit generated routes
🔍 Shallow nesting prevents deep URL structures
⚡ Check routes with rails routes command
routesrestresources

Custom Routes

Define custom routes and root

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✅ root route defines homepage (must be first)
💡 Use as: option to create custom path helper
🔍 Constraints validate route parameters
⚡ rails routes | grep posts to filter routes
routescustomhttp

Controllers

Controller Actions

Common controller patterns and responses

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✅ Use before_action for common setup code
💡 Strong parameters required for mass assignment
🔍 respond_to handles multiple formats
⚡ Use includes() to avoid N+1 queries
controllersactionscrud

Filters & Callbacks

Before/after/around filters for controller actions

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✅ before_action runs before controller actions
💡 Use only/except to limit filter scope
🔍 skip_before_action skips inherited filters
⚡ around_action wraps action execution
controllersfilterscallbacks

Models & Active Record

Model Associations

Define relationships between models

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✅ belongs_to creates foreign key relationship
💡 dependent: :destroy deletes associated records
🔍 has_many :through for many-to-many relationships
⚡ Use counter_cache to avoid COUNT queries
modelsassociationsrelationships

Validations

Validate model data before saving

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✅ Validations run before save/create/update
💡 Use presence: true for required fields
🔍 Custom validations via validate method
⚡ Conditional validations with if/unless
modelsvalidationsdata-integrity

Queries & Scopes

Query database with Active Record

ruby
✅ Use find_by instead of where().first
💡 includes() prevents N+1 query problems
🔍 Scopes make queries reusable and chainable
⚡ Use select() to fetch only needed columns
modelsqueriesactive-recordscopes

Callbacks

Lifecycle hooks for model operations

ruby
✅ Callbacks run automatically during object lifecycle
💡 before_validation runs before validations
🔍 Use conditional callbacks with if/unless
⚠️ Avoid complex logic in callbacks, use service objects
modelscallbackslifecycle