Ruby on Rails

1
Ruby on Rails

• Presenter Michael Mayer
• 30-March-2006
• Network Programming _at_ RPI
• This presentation was adapted from a ThoughtWise
  presentation
• By Obie Fernandez originally presented on
  10-March-2005.

2
Presentation Agenda

• Very brief overview of Ruby
• Description of Rails framework
• Questions and Answers
• Rails demo (if time allows)

3
Why Ruby?

• Write understandable code in few lines
  meta-programming
• Free (Very open license)
• Extensible
• Truly object oriented there are no primitives
• Why not Ruby?
• Lack of support for casting
• Lack of documentation
• Relatively small community

4
Some Coding Conventions

• Method Chainingprint array.uniq.sort.reverse
• (now thats meta-programming!)
• Method Names include ! and ?ary.sort!
• Iterators and Blocks vs. Loopsfiles.each
  file process(file)
• Case usage
• Class names begin with a Capital letter
• Constants are ALL_CAPS
• Everything else - method call or a local variable
• under_score instead of camelCase

5
Enough About Ruby!

• Time to talk about Ruby on Rails!

6
Rails in a Nutshell

• It is a rapid development framework a framework
  is simply a set of best practices and
  abstractions often accompanied by automation
  scripts that, in combination, make SW development
  with specific technologies easier.
• Create database-driven web applications according
  to the Model-View-Control pattern of separation.
• Favors Convention over Configuration!
• Mostly written by David H. Hannson
• A 37signals.com principal
• Maintained by an active OS community!

7
Rails Architecture
8
Model View Controller

• Model classes are the "smart" domain objects
  (e.g. Product) that hold business logic and know
  how to persist themselves to a database
• Views are HTML/XML templates
• Controllers handle incoming requests (e.g. Update
  Product) by manipulating the model and directing
  data to the view

9
ActiveRecord API

• Object/Relational Mapping Framework
• Model classes use this API
• Automatic mapping between columns and class
  attributes
• Declarative configuration via macros
• Dynamic finders
• Associations, Aggregations, Tree and List
  Behaviors
• Locking
• Validation rules
• Et cetera

10
ActiveRecord Associations

• Macro-like class methods for tying objects
  together through foreign keys
• Each adds a number of methods to the class
• In combination with migrations, allows your
  database to be DBMS agnostic

11
ActionController API

• Controllers defined as classes that execute and
  then either render a template or redirects
• An action is a public method on the controller
• Getting data in and out of controllers
• Request parameters available in the _at_params hash
  (and can be multidimensional)
• Web session exposed as _at_session hash
• Cookies exposed as _at_cookies hash
• Redirect scope provided by _at_flash hash (unique to
  Rails)

12
From Controller to View

• Rails gives you many rendering options
• Default template rendering follow naming
  conventions and magic happens
• Explicitly render to particular action
• Redirect to another action
• Render a string response (or no response)

13
Approaches to View Templating

• ERB Embedded Ruby
• Similar to JSPs lt and lt syntax or PHPs lt?
  syntax
• Easy to learn and teach to designers
• Execute in scope of controller
• Denoted with .rhtml extension
• XmlMarkup Programmatic View Construction
• Great for writing xml content
• Denoted with .rxml extension
• Embeddable in ERB templates

14
ERB Example
15
XmlMarkup Example
16
Layouts and Partials

• Templates in app/views/layouts/ with the same
  name as a controller will be automatically set as
  that controllers layout unless explicitly told
  otherwise
• Partials are sub-templates that render a single
  object
• Partial template files follow convention
• Easy API support for rendering collections of
  partials.

17
The Quest for Pretty URLs

• The responsibility of URL parsing is handled by
  Rails itself. Why?
• Not all webservers support rewriting
• Allows Rails to function out of the box on
  almost all webservers
• Facilitates definition of custom URLs
• Linked to URL helper methods such as url_for,
  link_to, and redirect_to
• Routing rules defined in config/routes.rb

18
routes.rb
ActionControllerRoutingRoutes.draw do map
Priority based on creation first created -gt
highest priority Keep in mind you can assign
values other than controller and action
You can have the root of your site routed by
hooking up '' just remember to delete
public/index.html. map.connect '', controller
gt "bakery" map.connect 'query/guid',
controller gt global", actiongt"query"
Allow downloading Web Service WSDL as a file with
an extension map.connect 'controller/service.ws
dl', action gt 'wsdl' map.connect
'controller/action/id Default end
19
Rails to the Rescue

• Actions that fail to perform as expected throw
  exceptions
• Exceptions can be rescued
• for public view (with a nice user-friendly
  explanation)
• for developers view (with tons of debugging
  information)
• By default, requests from localhost get
  developers view

20
Rake

• Rubys Build System
• Familiar to Ant users
• Your build file is a written in Ruby
• Basic build script provided with Rails project

21
The Rails Community

• The developer community around Rails is very
  helpful and excited
• Rails Wiki - http//wiki.rubyonrails.com/
• Rails Mailing List very active
• IRC Get instant answers to most questions.
  David and other Rails commiters are all regularly
  present

22
What did I leave out?

• ActionMailer API
• ActionWebService API
• ActiveSupport API
• Scaffolding
• Scripts and Generators
• Webrick web server
• Et cetera

23
Questions / Comments?

• Thanks for listening!
• Feel free to email me. I am one of your TAs after
  all
• mayerm_at_cs.rpi.edu
• Original presentation
• http//rubyforge.org/docman/view.php/251/158/Ruby
  20On20Rails.ppt

24
Demo

• Time to see some code!