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

API styles

If you recall from Chapter 5, Implementing Domain Logic, we created the following commands:

Figure 6.1 – Commands from the eventstorming session

If you observe carefully, there seem to be commands at two levels of granularity. Create LC Application and Update LC Application are coarse-grained, whereas the others are a lot more focused in terms of their intent. One possible decomposition of the coarse-grained commands can be as depicted here:

Figure 6.2 – Decomposed commands

In addition to just being more fine-grained than the commands in the previous iteration, the revised commands seem to better capture the user’s intent. This may feel like a minor change in semantics, but can have a huge impact on the way our solution is used by its ultimate end users. The question then is whether we should always prefer fine-grained APIs over coarse-grained ones. The answer can be a lot more nuanced. When designing...