A little engineering on Rails
Robert W. Hasker
Goals
• Intro to the Rails framework
▫ Basic concepts: MVC, Active Record
▫ A bit of Ruby
• Using Rails to build a website
• Myths and issues
The Rails Framework
• Basic goal: construct database-backed websites
• Multi-platform: popular OS’s, database engines
• Origins:
▫ Instiki by David Heinemeier Hansson
▫ Basecamp by 37signals
▫ Rails: domain-independent core
• Built on the Ruby language
▫ General-purpose language: scripting, applications
▫ Dynamically typed, “open” classes
Basic Concept: MVC
• Issue: how to separate logic from presentation?
• Classic solution: Model/View/Controller
▫ Model: domain-level data
▫ View: how the data is presented to the user
 Typically want multiple views
▫ Controller: logic linking the two
• Rails
▫ Model
▫ View
▫ Controller
= tables in a relational database
= web pages
= controller
Basic Concepts: Active Record
• Relational Databases: organize large amounts of
data
▫ Issue: no easy mapping to object-oriented design
• Active Record Pattern
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A design pattern first described by Martin Fowler
Object = table row w/ attributes stored as columns
Table = collection of objects
OOD = database (collection of tables)
 Rails: link classes through id fields in tables
Active Record Example
• Data for a simple voting system:
• As tables:
▫ create table questions (id int, body text,
start datetime, end datetime, primary
key(id));
▫ create table voters (id int, username text,
password text, primary key(id));
▫ create table vote_records (voter_id int, …);
• Benefit: can add operations as needed - active records
Using rails to build a voting application
• See http://www.uwplatt.edu/csse/tools/ruby/rails/rails-demo.html
Conclusion
• Rails: quick OO websites
▫ MVC: sound organization
▫ ActiveRecord: support good OO designs
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Focus on relationships, not queries
Less likely to forget a join, but supports full SQL
Not shown: does support inheritance
Navigation: keep the class diagram close at hand!
Conclusion…
• Design
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DRY: don’t repeat yourself
Convention, not configuration
Relationships are declared explicitly
Scaffolding: quick data entry (prototyping only)
Great development environment
 has full debugging support; separate dev/prod db’s
▫ Supports JavaScript/Ajax/etc.
 Explore Ajax support next time
Myths & Issues
• Myth: slow sites, doesn’t scale
▫ Supports many web servers
▫ Many optimizations probably belong elsewhere
▫ Technology improving
• Myth: only for specific types of projects
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Source: lots of simple examples out there
Can handle big problems
Don’t have to involve a database
See http://wiki.rubyonrails.org/rails/pages/RealWorldUsagePage1
• Issues
▫ Active Records: should have Table classes
▫ Ruby: run-time type checking requires lots of testing!
 But has good built-in testing support!
▫ Developers tempted to use all – pick level and stick to it
Resources
• Online tutorials
• Classic text: Agile Web Development with Rails
• Starting points:
▫ http://guides.rubyonrails.org/getting_started.html
▫ Beginning Rails: From Novice to Professional
 In library, but based on Rails 1.x
▫ Beginning Rails 3
 Available soon
• More detail: The Rails Way