Models and AR (cont'd)

acts_as_{ordered list, nested set, tree, taggable}
Validation
- Existence, uniqueness, numericality, length, format, exclusion/inclusion, acceptance
- Error messages auto-built
- When save, validations run. If fail, save fails and error messages are built and available
Before/after callbacks
- load, save, create

Models and AR (cont'd)

ModelClass.find()
- by id
- conditions, order, joins
- can use raw SQL or fragments
- find_by_X, find_by_X_and_Y created at runtime
Transactions
Observers
Class inheritance: single table

Models and AR (cont'd)

Database abstraction
- PostgreSQL, MySQL, Oracle, SQLite, DB2, Firebird, MS SQL, Sybase, Openbase
- Adapters approx. 100 lines of code
Connection pool
Multiple databases supported, can specify per class

Magic column names

id
created_{at,on}, updated_{at,on}
type
position
parent_id
XXX_id (foreign keys)
lock_version for optimistic locking

Views

Templates

.rhtml
- XHTML
- Minimal Ruby in page; behavior is in controllers and models
- Uses ERb, similar to PHP but with Ruby
.rxml
- Constructs XML using Ruby code
- Example use: build RSS
.rjs (Ruby code JavaScript generator)
- Generate instructions on how to modify an already-rendered page
- Create/refresh/replace DOM components
- Apply AJAX effects

.rxml: XML builder code uses method_missing; xml.foo outputs <foo>
.rjs: Not necessary to use RJS for AJAX

Views (cont'd)

Large number of methods available
- link_to and friends (link_to_unless_current, link_to_remote)
- forms, input fields, naming conventions to work with model objects
- cycle for even/odd CSS classes
You don't hard-code URLs, you use link_to, image_tag and friends and specify controller and action; same for stylesheet_link_tag, javascript_include_tag

Views (cont'd)

Partials
- Views can render partials
- Pass variables into partials for local use
Pagination
Helpers: common code for views
- Rails comes with number and currency formatting, string truncation and pluralization, highlighting substrings, more
AJAX and DHTML

AJAX
- form submission, live updater
DHTML
- effects (slide, poof)
- script.aculo.us, mir.aculo.us
- drag and drop

Controllers

Present models to views, take view data and hand back to models
One controller has many actions; each action roughly corresponds to a Web page and REST URL
Same action can render any of HTML/XML/RSS output, based e.g. on input URL/template file extension
Redirect
Layouts: application-wide, per controller, or per action

Controllers (cont'd)

Routes
- Default mapping of URLs to controller action
- Can override and manipulate URLs piece by piece
Before filters: e.g., requires_login
Can render any view or partial
Scaffolding
- Auto-generated CRUD screens for a model
- Explicit when generate controller or implicit with 1 line code

Controllers (cont'd)

params array contains GET/POST request values
- Form input field functions' naming conventions map to model ivars
Protection against destructive GET requests: can say that action must use POST
flash[] for temporary messages like error messages or notifications

Action Mailer

Sending email from app
Text or HTML
Can send multipart messages with attachments
Can use rhtml as template for message body
When testing, can config (using env file) to send emails to an array in memory

Action Web Service

Add Web services to your app
Brain-dead simple
API class declares Web service methods with inputs and outputs
Controller implements methods (can delegate instead)
Can accept XML-RPC or SOAP/RPC
Auto-generates WSDL
Invocation scaffold

Can set namespace

Creating a Rails Project

rails appname
Directory structure: a place for everything, and everything in its place
- models, views, controllers, helpers
- database scripts
- documentation
- configuration
- testing
- logs
- static HTML, JavaScript, sytlesheets, 404 & 500, robots.txt
  - comes with JavaScript for AJAX, drag and drop, pagination, much more

Creating a Rails Proj (cont'd)

Scripts (see next slide)
Built-in pure-Ruby Web server (not fastest or best)
Rakefile
- Test tasks, doc tasks, db schema tasks, rails tasks (freeze, update)
Testing harness
Routing

Development and Testing

Scripts
- generate creates models, contollers, integration tests, mailer, migration, plugin, scaffold, session_migration, web_service
  - Generating a model or controller generates test cases automatically
  - Generating a model generates a database migration script automatically
  - Can write your own generators. Examples:
    - Localization
    - Login, salted login
  - Finding more generators:
    - Use Gem's search feature
    - http://rubyonrails.org/show/Generators
  - See also Extending Rails

Dev. and Testing (cont'd)

Scripts (cont'd)
- console and runner scripts
- Performance subdir: benchmarker, profiler
- Process subdir: spinner, reaper, spawner for Fast CGI listner management
- Default WEBrick server launcher

Dev. and Testing (cont'd)

Environments
- With the flick of an env var or command line switch, connect to different database and use completely different set of configuration values
- In dev env, code changes detected automatically; almost all classes refreshed for every page
- ...so the development cycle is "edit code or database, refresh browser"
  - See Caching below

Dev. and Testing (cont'd)

Available documentation
- See Resources
- Rails mailing list very helpful
- Comes with docs: gem_server
- Books
  - Agile Web Development with Rails
  - Rails Recipes
  - New Rails Deployment Configuration book in beta
Development Environments
- Eclipse: Rad Rails (editing, app server, more)
- TextMate (Mac OS X only)

Agile Web Dev: : 2nd ed already, paper quickly becomes out of date: pragprog PDF and mlists to keep up

Dev. and Testing (cont'd)

Testing
- Unit tests
- Controller-level tests
- Web service API-level tests
- Integration tests
- (Probs w/multiple db conns during testing)
Fixtures define test data that is loaded as needed before each test is run
- By default uses transactions to eliminate load times

Dev. and Testing (cont'd)

Migrations
- Script creates/drops tables and lets you run any Ruby code you want with full access to all your Model objects
- Each has up and down methods
- Foreign key support lacking
  - I wrote support; you can have it
Scaffolding
Logging
WEBrick (do not use), Mongrel (discussed below)

Dev. and Testing (cont'd)

Rake
- Db (re)create schema
- Running tests
- Create sessions table
- Can create custom tasks
Documentation generation: RDoc
Mocks: if class found in mock dir, it's used
- Ruby's open nature means you can modify existing classes
- Example: SystemClock

Extending Rails

Components, plugins, and engines
Components allow you to share code across pages
Plugins and engines
- Allow you to share code between Rails applications
- Can contain schema, models, controllers, views, behavior

(Don't spend too much time on this section.)

Extending Rails (cont'd)

Components
- Made up of controllers, helpers, and views
- Example: shopping cart
- Does not follow file structure
- Components falling out of favor
- Can often use partials instead

Extending Rails (cont'd)

Plugins
- Have init code, can be used to extend Rails base classes
- Go into vendor/plugins directory
- Examples
  - Extended scaffolding: works with associations
  - acts_as_chunky_bacon (in other words, writing new AR class behaviors)
  - Email notification on errors
  - Common before_filters
  - Web service infrastructure

Extending Rails (cont'd)

Engines are more like a vertical slice of behavior
- Let you add application-level behavior without affecting existing code.
- Example: managing users and permissions
- http://rails-engines.rubyforge.org
Components vs. Plugins vs. Engines

Deployment

Apache, lightspeed, lighttpd, Mongrel, etc.
- lighttpd ("lighty"): fast, small, Web server with good feature set
- IIS possible
We'll discuss performance and scaling in a moment
Mongrel
- Does not use SCGI; Rails runs inside Mongrel
- Don't need lighttpd or Apache
- Pool of thread workers
- Plugins
  - Clustering

Deployment (cont'd)

Capistrano
- Not part of Rails
- You provide a "recipe" describing servers and their roles, plus shell script snippets
- Allows you to roll bad version out of production and revert to previous release
- Runs database migrations
- Very little of Capistrano is Rails-specific
- Capistrano is really a tool that executes commands in parallel on multiple servers
- Uses SSH, SVN/CVS/Darcs
- Task for disabling/enabling Web (flips in "maintenance" pages)
- Restart

Deployment (cont'd)

Migrations
Versioning of Rails itself and gems
- Rake tasks
  - Lock to current gems (unpack into vendor/rails), unlock
  - Lock/unlock from edge rails
  - Update scripts with latest Rails version's scripts
Cron jobs: runner script

Performance and Scaling

Some well-known sites
- Ruby on Rails site: 3,500–4,500 TBs/month (approx. 10–15 Mbps)
- Basecamp, Backpack, Campfile, Ta-Da Lists, Writeboard
- 43 {Things, Places, People}
- CD Baby — see Derek Silvers' O'Reilly blogs
- Odeo: podcast/audio files
Guidelines
- Scalability means resource expansion, not speed or high performance
- Measure requests per second, not users per second

Perf. and Scaling (cont'd)

It's Boring to Scale with Ruby on Rails
- Share nothing (state out of app servers, into db/memcached/shared network drive)
- Load balance between all tiers (can be software load balancers)
- This allows you to add Web and app servers without changing anything
- Scaling the database is the hard part
  - Once get beyond master/slave setup, you start doing data partitioning
- Economic issues determine next steps — see article
- Remember, Rails is only one part of the whole deployment

"We've gone the easy route and merely followed what makes Yahoo!, LiveJournal, and other high-profile LAMP stacks scale high and mighty."
Load balancers -> web servers -> load balancers -> app servers -> load balancers -> database/memcached/shared network drive servers.
"The point is that the cost per request is plummeting, but the cost of programming is not."

Perf. and Scaling (cont'd)

Caching
- Page caching
- Action caching
- Fragment caching
- Can expire explicitly, implicitly, or with sweepers
- Caching can be turned on/off in environment files
  - By default, only enabled in production environment

Page caching
- handled by Web server, for relatively static (e.g., product desc.)
Action caching
- controller invoked, before filters run, but action not invoked if already cached
Fragment caching
- use cache() method in view to surround output you want cached
In controller, use caches_page and caches_action class methods

Perf. and Scaling (cont'd)

Sessions: on file system by default; can use database with flick of a switch (and a database migration); can use memcached
Scale With Rails (pdf)
- Solaris, Sun T1000's, Ultrasparc T1, ZFS
- Scale with Rails workshops: missed NYC, Aug. 23-24 LA, Oct. 25-26 Frankfurt
Zed on Ruby, Rails, Mongrel, and More
A Look at Common Performance Problems in Rails
Ruby itself
- YARV (Yet Another Ruby VM)/Rite
- C and SWIG

The Future

Edge Rails is always available via Subversion
ActiveResource
- Model objects become REST-based client proxies to remote services
- Maps CRUD to REST using HTTP commands GET, POST, PUT, and DELETE

Person.find(1)      # becomes an HTTP GET
Person.find(:all)   # ditto
some_person.save    # (update)   HTTP POST
Person.new.save     # (create)   HTTP PUT
some_person.destroy #            HTTP DELETE

Resources

http://www.rubyonrails.org
http://www.rubyonrails.org/docs
This talk online
My del.icio.us tags
- http://del.icio.us/jimm/rails
- http://del.icio.us/jimm/ruby
http://www.ruby-doc.org

The End

So...is it hot, or is it not?

Ruby On Rails – An Introduction

NYC CTO Club • July 12, 2006

Ruby on Rails

Jim Menard

jim@jimmenard.com

Shiny Things

Agenda

QotD

What is Ruby on Rails?

What is RoR? (cont'd)

Philosophy

Philosophy (cont'd)

Ruby

Architecture

Architecture (cont'd)

Architecture (cont'd)

Models and AR

Models and AR (cont'd)

Models and AR (cont'd)

Models and AR (cont'd)

Views

Views (cont'd)

Views (cont'd)

Controllers

Controllers (cont'd)

Controllers (cont'd)

Action Mailer

Action Web Service

Creating a Rails Project

Creating a Rails Proj (cont'd)

Development and Testing

Dev. and Testing (cont'd)

Dev. and Testing (cont'd)

Dev. and Testing (cont'd)

Dev. and Testing (cont'd)

Dev. and Testing (cont'd)

Dev. and Testing (cont'd)

Extending Rails

Extending Rails (cont'd)

Extending Rails (cont'd)

Extending Rails (cont'd)

Deployment

Deployment (cont'd)

Deployment (cont'd)

Performance and Scaling

Perf. and Scaling (cont'd)

Perf. and Scaling (cont'd)

Perf. and Scaling (cont'd)

The Future

Resources

The End