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!
About the Authors
Table of Contents
-
Preface
- First Book: Domain-Driven Design in PHP
- DDD acceptance has rapidly grown
- Second Book: CQRS by Example
- Who Should Read This Book
- Summary of Chapters
- Code, Typos, and Examples
- Slack Channel
-
Acknowledgements
- Cover
- Contributors
-
About the Authors
- Carlos Buenosvinos
- Christian Soronellas
- Keyvan Akbary
-
CQRS and Domain-Driven Design
- What is all the fuzz about?
- Why Domain-Driven Design Matters
- The Three Pillars of Domain-Driven Design
- Considering Domain-Driven Design
- The Tricky Parts
- Wrap-Up
-
A Journey Towards CQRS
- Introducing Cheeper, a Twitter Clone
- Architectural Styles
- A brief analysis
- Hexagonal Architecture Potential Limitations
- Wrap-Up
-
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
- Wrap-Up
-
Command Side and the Write Model
- Commands
- Command Handlers
- Command Bus
- Plumbing all together
- Wrap-Up
-
Query Side and the Read Models
- Queries
- Query Handlers
- Query Bus
- Plumbing all together
- Wrap-Up
- The End
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