Book Image

Domain-Driven Design with Java - A Practitioner's Guide

By : Premanand Chandrasekaran, Karthik Krishnan
Book Image

Domain-Driven Design with Java - A Practitioner's Guide

By: Premanand Chandrasekaran, Karthik Krishnan

Overview of this book

Domain-Driven Design (DDD) makes available a set of techniques and patterns that enable domain experts, architects, and developers to work together to decompose complex business problems into a set of well-factored, collaborating, and loosely coupled subsystems. This practical guide will help you as a developer and architect to put your knowledge to work in order to create elegant software designs that are enjoyable to work with and easy to reason about. You'll begin with an introduction to the concepts of domain-driven design and discover various ways to apply them in real-world scenarios. You'll also appreciate how DDD is extremely relevant when creating cloud native solutions that employ modern techniques such as event-driven microservices and fine-grained architectures. As you advance through the chapters, you'll get acquainted with core DDD’s strategic design concepts such as the ubiquitous language, context maps, bounded contexts, and tactical design elements like aggregates and domain models and events. You'll understand how to apply modern, lightweight modeling techniques such as business value canvas, Wardley mapping, domain storytelling, and event storming, while also learning how to test-drive the system to create solutions that exhibit high degrees of internal quality. By the end of this software design book, you'll be able to architect, design, and implement robust, resilient, and performant distributed software solutions.
Table of Contents (17 chapters)
Part 1: Foundations
Part 2: Real-World DDD
Part 3: Evolution Patterns

Implementing the command side

In this section, we will focus on implementing the command side of the application. This is where we expect all the business logic of the application to be implemented. Logically, it looks like the following figure:

Figure 5.2 – Traditional versus CQRS architecture

The high-level sequence on the command side is described here:

  1. A request to mutate state (command) is received.
  2. In an event-sourced system, the command model is constructed by replaying existing events that have occurred for that instance. In a state-stored system, we would simply restore state by reading state from the persistence store.
  3. If business invariants (validations) are satisfied, one or more domain events are readied with the intention to be published.
  4. In an event-sourced system, the domain event is persisted on the command side. In a state-stored system, we would update the state of the instance in the persistence store.
  5. The...