Ruby on Rails Introduction

Lecture Notes for CS349W
Fall Quarter 2008
John Ousterhout

• Probably the most high-level Web application framework.
• 2 components:
  • Ruby programming language: dynamic and object-oriented. (won't cover in detail in this class)
  • Rails framework: set of Ruby classes for creating Web applications.
• Rails applications have an MVC (model-view-controller) structure:
  • Model: manages the application data via ORM
    • Each class encapsulates the data in a particular database table.
  • View: templates that generate Web pages.
  • Controller: glue between the model and view:
    • Responds to incoming HTTP requests
    • Fetches/modifies data in the models
    • Invokes a view to generate the Web page
  • The MVC pattern has been around since the late 1970's; originally conceived in the Smalltalk project at Xerox PARC.
• Key element of Rails framework: "convention over configuration":
  • Many conventions for how you should structure your applications (e.g., directory structure for files)
  • Tools implement many of the conventions automatically
  • If you follow the conventions, many things happen automatically:
    • If there is a database table named Employees with a column salary, Rails will automatically define a class Employee with an instance variable named salary; this field will be displayed in a form element named salary for editing.
  • Simplifies things greatly over other frameworks where all of the configuration must be specified explicitly in complex XML files; avoids cumbersome repetition (DRY).