CQRS by Example
CQRS by Example
Command-Query Responsibility Segregation is an architectural style for developing applications that split the Domain Model in Read and Write operations in order to maximize semantics, performance, and scalability. What are all the benefits of CQRS? What are the drawbacks? In which cases does it worth applying it? How does it relate to Hexagonal Architecture? How do we properly implement the Write Model and Read Models? How do we keep in sync both sides? What are the following steps to move towards Event Sourcing? This book will answer all these questions and many more, guided through lots of practical examples. Brought to you by the same authors behind "Domain-Driven Design in PHP".
About the Book
Four years have passed since our first publication, we established what we think is a solid ground for DDD building blocks and Hexagonal Architecture. It is time to explore how to solve the limitations some projects may face at scale.
We think CQRS is the next natural step forward and we want to guide you through it.CQRS is usually discussed along with Event Sourcing, a pattern where application state is a projection of the Domain Events that happen through its lifetime. Event Sourcing relies on having a stream of Domain Events to reconstitute state. Something convenient for operations that modify the state of the application, known as Commands; however, querying the system requires some special mechanisms that aren't that trivial. We can say than in Event Sourced systems CQRS is mandatory in order to generate the required information to be able to query later, but the opposite isn't true. We can develop a CQRS system without Event Sourcing, so worry not, this book won't cover Event Sourcing.
In this book, we'll explore Hexagonal Architecture drawbacks, and we'll dive into CQRS by exploring plenty of real examples that you can use in your projects. Even though code examples are written in PHP, the patterns and techniques described in this book are applicable to any programming language and likely any paradigm you may be using. We can't thank you enough for purchasing this book and be an active contributor of Domain-Driven Design, Hexagonal Architecture, and CQRS!
Table of Contents
- Foreword by Marco Pivetta
-
Preface
- Domain-Driven Design in PHP
- DDD acceptance has rapidly grown
- CQRS by Example
- Who Should Read This Book
- Summary of Chapters
- Code, Typos, and Examples
- Acknowledgements
-
About the Authors
- Carlos Buenosvinos
- Christian Soronellas
- Keyvan Akbary
-
CQRS and Domain-Driven Design
- What’s All the Fuss About?
- Why Domain-Driven Design Matters
- The Three Pillars of Domain-Driven Design
- Considering Domain-Driven Design
- The Tricky Parts
- Wrapup
-
A Journey Toward CQRS
- Introducing Cheeper, a Twitter Clone
- Architectural Styles
- A Brief Analysis
- Potential Limitations of Hexagonal Architecture
- Wrapup
-
Anatomy of CQRS
- Cheeper Use Case Analysis
- Cheeper à la CQRS
- CQRS Overview
- Other CQRS Components
- Two Sides of the Same Coin
- The Command Side
- The Query Side
- Syncing the Command and Query Sides
- Wrapup
-
Command Side and the Write Model
- Commands
- Command Handlers
- Command Bus
- Putting It All Together
- Wrapup
-
Query Side and the Read Models
- Queries
- Query Handlers
- Query Bus
- Putting It All Together
- Wrapup
-
Synchronizing the Write and the Read Models
- Multiple Read Models
- Synchronization Strategies
- Wrapup
-
The Full Picture
- The Timeline Use Case
- Posting a Cheep
- Command
- Command Bus
- Command Handler
- Domain Event
- Event Bus
- Event Handler
- Projection
- Projection Bus
- Projection Handler
- Fetching the Timeline
- Query
- Query Bus
- Query Handler
- Wrapup
-
Optimizations and Edge Cases
- Relying on Multiple Read Models
- Incremental Projections
- Race Conditions
- Troubles with Events
- Duplicated Messages
- Missing Events
- Dealing with Inconsistencies
- Wrapup
-
CQRS and Event Sourcing
- CQRS Biggest Challenge
- Recreating State from Past Events
- Introducing the Event Store
- Changes in Repositories
- Changes in Entities or Aggregates
- Changes in Projections
- Event Sourcing Trade-Offs
- Wrapup
-
Demo Time
- Before we Begin
- Starting the Application
- Nothing Up In My Sleeve
- Signing Up New Authors
-
Consuming
NewAuthorSigned
Events - Following Other Authors
-
Consuming
FollowCommand
Commands - Verifying Author’s Followers
-
Consuming
AuthorFollowed
Events - Posting Cheeps
-
Consuming
PostCheepCommand
Commands -
Consuming
CheepPosted
Events -
Consuming
AddCheepToTimelineProjection
Projections - Verifying Author’s Timeline
- Wrapup
- The End
- Bibliography
The Leanpub 60-day 100% Happiness Guarantee
Within 60 days of purchase you can get a 100% refund on any Leanpub purchase, in two clicks.
See full terms
Do Well. Do Good.
Authors have earned$11,600,486writing, publishing and selling on Leanpub, earning 80% royalties while saving up to 25 million pounds of CO2 and up to 46,000 trees.
Learn more about writing on Leanpub
Free Updates. DRM Free.
If you buy a Leanpub book, you get free updates for as long as the author updates the book! Many authors use Leanpub to publish their books in-progress, while they are writing them. All readers get free updates, regardless of when they bought the book or how much they paid (including free).
Most Leanpub books are available in PDF (for computers), EPUB (for phones and tablets) and MOBI (for Kindle). The formats that a book includes are shown at the top right corner of this page.
Finally, Leanpub books don't have any DRM copy-protection nonsense, so you can easily read them on any supported device.
Learn more about Leanpub's ebook formats and where to read them
Top Books
C++20 - The Complete Guide
Nicolai M. JosuttisAll new language and library features of C++20 (for those who know previous C++ versions).
The book presents all new language and library features of C++20. Learn how this impacts day-to-day programming, to benefit in practice, to combine new features, and to avoid all new traps.
Buy early, pay less, free updates.
Other books:
Cronache di Domain-Driven Design
Francesco Strazzullo, Matteo Baglini, Gianluca Padovani, Emanuele DelBono, Marco Consolaro, Alessandro Colla, Uberto Barbini, Alberto Acerbis, Julie Camosseto, DDD Open, and Alberto BrandoliniCronache di Domain-Driven Design: un libro corale in italiano fatto di storie indipendenti tra loro, che sono il risultato dell’applicazione di Domain-Driven Design su progetti reali.
Ansible for DevOps
Jeff GeerlingAnsible is a simple, but powerful, server and configuration management tool. Learn to use Ansible effectively, whether you manage one server—or thousands.
Jetpack Compose internals
Jorge CastilloJetpack Compose is the future of Android UI. Master how it works internally and become a more efficient developer with it. You'll also find it valuable if you are not an Android dev. This book provides all the details to understand how the Compose compiler & runtime work, and how to create a client library using them.
OpenIntro Statistics
David Diez, Christopher Barr, Mine Cetinkaya-Rundel, and OpenIntroA complete foundation for Statistics, also serving as a foundation for Data Science.
Leanpub revenue supports OpenIntro (US-based nonprofit) so we can provide free desk copies to teachers interested in using OpenIntro Statistics in the classroom and expand the project to support free textbooks in other subjects.
More resources: openintro.org.
R Programming for Data Science
Roger D. PengThis book brings the fundamentals of R programming to you, using the same material developed as part of the industry-leading Johns Hopkins Data Science Specialization. The skills taught in this book will lay the foundation for you to begin your journey learning data science. Printed copies of this book are available through Lulu.
Functional event-driven architecture: Powered by Scala 3
Gabriel VolpeExplore the event-driven architecture (EDA) in a purely functional way, mainly powered by Fs2 streams in Scala 3!
Leverage your functional programming skills by designing and writing stateless microservices that scale, powered by stateful message brokers.
Mastering STM32 - Second Edition
Carmine NovielloWith more than 1200 microcontrollers, STM32 is probably the most complete ARM Cortex-M platform on the market. This book aims to be the first guide around that introduces the reader to this exciting MCU portfolio from ST Microelectronics and its official CubeHAL and STM32CubeIDE development environment.
CCIE Service Provider Version 4 Written and Lab Exam Comprehensive Guide
Nicholas RussoThe service provider landscape has changed rapidly over the past several years. Networking vendors are continuing to propose new standards, techniques, and procedures for overcoming new challenges while concurrently reducing costs and delivering new services. Cisco has recently updated the CCIE Service Provider track to reflect these changes; this book represents the author's personal journey in achieving that certification.
CCIE SP v5.0
Łukasz Bromirski, Piotr Jablonski, and Nicholas RussoAre you striving to prepare to and pass CCIE SP lab exam? Take the opportunity and get this workbook! With the attached initial cfg files you will prepare yourself for the CCIE SP exam as well as learn SP technologies applicable to all kinds of today modern networks! This workbook covers blueprint topics and provides challenging examples.
Top Bundles
- #1
Software Architecture for Developers: Volumes 1 & 2 - Technical leadership and communication
2 Books
"Software Architecture for Developers" is a practical and pragmatic guide to modern, lightweight software architecture, specifically aimed at developers. You'll learn:The essence of software architecture.Why the software architecture role should include coding, coaching and collaboration.The things that you really need to think about before... - #2
Practical FP in Scala + Functional event-driven architecture
2 Books
Practical FP in Scala (A hands-on approach) & Functional event-driven architecture, aka FEDA, (Powered by Scala 3), together as a bundle! The content of PFP in Scala is a requirement to understand FEDA so why not take advantage of this bundle!? - #3
All the Books of The Medical Futurist
6 Books
We put together the most popular books from The Medical Futurist to provide a clear picture about the major trends shaping the future of medicine and healthcare. Digital health technologies, artificial intelligence, the future of 20 medical specialties, big pharma, data privacy, digital health investments and how technology giants such as Amazon... - #4
CCIE Service Provider Ultimate Study Bundle
2 Books
Piotr Jablonski, Lukasz Bromirski, and Nick Russo have joined forces to deliver the only CCIE Service Provider training resource you'll ever need. This bundle contains a detailed and challenging collection of workbook labs, plus an extensively detailed technical reference guide. All of us have earned the CCIE Service Provider certification... - #6
Pattern-Oriented Memory Forensics and Malware Detection
2 Books
This training bundle for security engineers and researchers, malware and memory forensics analysts includes two accelerated training courses for Windows memory dump analysis using WinDbg. It is also useful for technical support and escalation engineers who analyze memory dumps from complex software environments and need to check for possible... - #7
Modern C++ Collection
3 Books
Get All about Modern C++C++ Standard Library, including C++20Concurrency with Modern C++, including C++20C++20Each book has about 200 complete code examples. Updates are included. When I update one of the books, you immediately get the updated bundle. You can expect significant updates to each new C++ standard (C++23, C++26, .. ) and also... - #9
Retromat eBook Bundle for Agile Retrospectives
2 Books
If you facilitate retrospectives this bundle is for you: "Plans for Retrospectives" helps beginners learn the lay of the land with tried-and-true plans. Once you know your way around, "Run great agile retrospectives" contains all 135+ activities in Retromat for you to mix and match.