Component-Based Rails Applications: Large Domains Under Control, 1st edition

  • Stephan Hagemann

Component-Based Rails Applications: Large Domains Under Control

ISBN-13:  9780134774589

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Use Components to Improve Maintainability, Reduce Complexity, and Accelerate Testing in Large Rails Applications

“This book gives Ruby pros a comprehensive guide for increasing the sophistication of their designs, without having to forsake the principles of elegance that keep them in our corner of the software world.”

–Obie Fernandez, author, The Rails™ 5 Way, Fourth Edition

As Rails applications grow, even experienced developers find it difficult to navigate code bases, implement new features, and keep tests fast. Components are the solution, and Component-Based Rails Applications shows how to make the most of them.


Writing for programmers and software team leads who are comfortable with Ruby and Rails, Stephan Hagemann introduces a practical, start-to-finish methodology for modernizing and restructuring existing Rails applications.


One step at a time, Hagemann demonstrates how to revamp Rails applications to exhibit visible, provably independent, and explicitly connected parts–thereby simplifying them and making them far easier for teams to manage, change, and test. Throughout, he introduces design concepts and techniques you can use to improve applications of many kinds, even if they weren’t built with Rails or Ruby.

  • Learn how components clarify intent, improve collaboration, and simplify innovation and maintenance
  • Create a full Rails application within a component, from first steps to migrations and dependency management
  • Test component-based applications, manage assets and dependencies, and deploy your application to production
  • Identify the seams in an existing Rails application, and refactor it to extract components
  • Master a scripted, repeatable approach for refactoring Rails applications of any size
  • Use component-based Rails with two popular structural patterns: hexagonal and DCI architecture
  • Leverage your new component skills with other frameworks and languages
  • Overcome the unique challenges that arise as you componentize Rails applications

If you’re ready to simplify and revitalize your complex Rails systems, you’re ready for Component-Based Rails Applications.

Register your book for convenient access to downloads, updates, and/or corrections as they become available. See inside book for details.

Table of contents

Foreword xi

Preface xiii

Acknowledgments xxi

About the Author xxiii

Chapter 1: Introduction to Component-Based Rails Applications 1

1.1 Component-Based Rails 2

1.2 Benefits of Component-Based Applications 4

1.3 Component-Based Ruby 13

1.4 The Application Continuum 14

1.5 Related Works 15


Chapter 2: Creating a Component-Based Application 17

2.1 The Entire App Inside a Component 18

2.2 ActiveRecord and Handling Migrations within Components 27

2.3 Handling Dependencies within Components 34


Chapter 3: Tooling for Components 49

3.1 Testing a Component 50

3.2 Testing the Main Application 65

3.3 Asset Loading for Components 74

3.4 Switching Databases 82

3.5 Deploying to Platforms-as-a-Service 86

3.6 Updating Application Dependencies 90

3.7 Proposal for a Different Application Root—Showcasing the Difference of Components’ Structure 99


Chapter 4: Component Refactorings: Extracting Components Out of Components 111

4.1 Determining What to Extract: Bottom-Up 112

4.2 Refactoring: Extract Domain Gem—Predictor 120

4.3 Determining What to Extract: Top-Down 139

4.4 Refactoring: Pulling Up a UI Component—TeamsAdmin, GamesAdmin, PredictionUI, WelcomeUI 150

4.5 Refactoring: Pushing Down a Model Component—Teams, Games 168

4.6 Refactoring: Improve Naming of Component—AppComponent to WebUI 183

4.7 More Component Refactoring Patterns 189


Chapter 5: From Ball of Mud to First Components 195

5.1 Small Steps 196

5.2 One Big Step 196


Chapter 6: Component-Based Rails in Relation to Other Patterns 211

6.1 Hexagonal Architecture 212

6.2 Data-Context-Integration (DCI) 227


Chapter 7: Components in Other Languages 237

7.1 Kotlin, Java, and Gradle 238

7.2 .NET / C 241

7.3 Conclusion 243


Appendix 245

A.1 Plain versus --full versus --mountable Engines 245

A.2 How Do Engine Routes and Engine Mounting Work? 254

A.3 Additional Testing with Older Versions of Rails 261


Index 265

Published by Addison-Wesley Professional (June 22nd 2018) - Copyright © 2018