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Ruby Science

The reference for writing fantastic Rails applications

You build web applications, and you love Ruby on Rails because it provides a framework for developing applications that are are fast, fun, and easy to change. Over time these applications can become bloated, development slows down, and changes to the codebase become painful.

This book was written to help you learn to detect emerging problems in your codebase; we’ll deliver the solutions for fixing them, and maintaining an application that will be fun to work on for years to come.

Download a free sample chapter.

More than just a book

In addition to the book (in HTML, PDF, EPUB, and Kindle formats), you also get a complete example application.

The book is written using Markdown and distributed via GitHub. When you purchase, we give you access directly to the repository, so you can use the GitHub comment and issue features to give us feedback about what we’ve written and what you’d like to see. Last but not least, also included is a Ruby on Rails reference application. What the book describes and explains, the example app demonstrates with real, working code. Fully up to date for Rails 3.2.

When you purchase Ruby Science, you get access all future updates to the book and example application.

Table of Contents


Code Smells

  • Long Method
  • Large Class
  • Feature Envy
  • Case Statement
  • High Fan-out
  • Shotgun Surgery
  • Divergent Change
  • Long Parameter List
  • Duplicated Code
  • Uncommunicative Name
  • Single Table Inheritance (STI)
  • Parallel Inheritance Hierarchies*
  • Comments
  • Mixin
  • Callback


  • Replace Conditional with Polymorphism
  • Replace conditional with Null Object
  • Extract method
  • Rename Method
  • Extract Class
  • Extract Value Object
  • Extract Decorator
  • Extract Partial
  • Extract Validator
  • Introduce Explaining Variable
  • Introduce Observer
  • Introduce Form Object
  • Introduce Parameter Object
  • Use class as Factory
  • Move method
  • Inline class
  • Inject dependencies
  • Replace Subclasses with Strategies
  • Replace mixin with composition
  • Replace Callback with Method
  • Use convention over configuration
  • Introduce Visitor


  • DRY
  • Single responsibility principle
  • Tell, Don’t Ask
  • Law of Demeter
  • Composition over inheritance
  • Open/closed principle
  • Dependency inversion principle

Ruby Science was written by Joe Ferris, Harlow Ward, and thoughtbot.

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  • You'll get .pdf, .mobi, .epub, and .html files
  • PDF Length227 pages


Ruby Science

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