Ferris Joe, Ward Harlow. Ruby Science

Thoughtbot, 2014. — 227 p.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.Code Smells
Long Method
Large Class
Feature Envy
Case Statement
Shotgun Surgery
Divergent Change
Long Parameter List
Duplicated Code
Uncommunicative Name
Single Table Inheritance (STI)
Comments
Mixin
CallbackSolutions
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 Form Object
Introduce Parameter Object
Introduce Facade
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 configurationPrinciples
DRY
Single responsibility principle
Tell, Don’t Ask
Law of Demeter
Composition over inheritance
Open/closed principle
Dependency inversion principle