Implementing Domain-Driven Design

Product Author Bios

Vaughn Vernon is a veteran software craftsman, with more than 25 years of experience in software design, development, and architecture. Vaughn is a thought leader in simplifying software design and implementation using innovative methods in distributed computing. Vaughn has been programming with object-oriented languages since the 1980s and applying the tenets of Domain-Driven Design since his Smalltalk domain modeling days in the early 1990s. His experience spans a wide range of business domains, including aerospace, environmental, geospatial, insurance, medical and health care, and telecommunications. He has also succeeded in technical endeavors creating reusable frameworks, libraries, and implementation acceleration tools. Vaughn consults and speaks internationally, and has taught his Implementing Domain-Driven Design classes on multiple continents. You can read more about his latest efforts at www.VaughnVernon.co and follow him on Twitter here: @VaughnVernon.

“For software developers of all experience levels looking to improve their results, and design and implement domain-driven enterprise applications consistently with the best current state of professional practice, Implementing Domain-Driven Design will impart a treasure trove of knowledge hard won within the DDD and enterprise application architecture communities over the last couple decades.”

–Randy Stafford, Architect At-Large, Oracle Coherence Product Development

“This book is a must-read for anybody looking to put DDD into practice.”

–Udi Dahan, Founder of NServiceBus

Implementing Domain-Driven Design presents a top-down approach to understanding domain-driven design (DDD) in a way that fluently connects strategic patterns to fundamental tactical programming tools. Vaughn Vernon couples guided approaches to implementation with modern architectures, highlighting the importance and value of focusing on the business domain while balancing technical considerations.

Building on Eric Evans’ seminal book, Domain-Driven Design, the author presents practical DDD techniques through examples from familiar domains. Each principle is backed up by realistic Java examples–all applicable to C# developers–and all content is tied together by a single case study: the delivery of a large-scale Scrum-based SaaS system for a multitenant environment.

The author takes you far beyond “DDD-lite” approaches that embrace DDD solely as a technical toolset, and shows you how to fully leverage DDD’s “strategic design patterns” using Bounded Context, Context Maps, and the Ubiquitous Language. Using these techniques and examples, you can reduce time to market and improve quality, as you build software that is more flexible, more scalable, and more tightly aligned to business goals.

Coverage includes

• Getting started the right way with DDD, so you can rapidly gain value from it
• Using DDD within diverse architectures, including Hexagonal, SOA, REST, CQRS, Event-Driven, and Fabric/Grid-Based
• Appropriately designing and applying Entities–and learning when to use Value Objects instead
• Mastering DDD’s powerful new Domain Events technique
• Designing Repositories for ORM, NoSQL, and other databases

Related Article

An Interview with Vaughn Vernon on Implementing Domain-Driven Design

Online Sample Chapter

Implementing Domain-Driven Design: Aggregates

Table of Contents

Chapter 1: Getting Started with DDD          1

Can I DDD?    2

Why You Should Do DDD    6

How to Do DDD    20

The Business Value of Using DDD    25

The Challenges of Applying DDD    29

Fiction, with Bucketfuls of Reality    38

Wrap-Up    41

Chapter 2: Domains, Subdomains, and Bounded Contexts         43

Big Picture   43

Why Strategic Design Is So Incredibly Essential    53

Real-World Domains and Subdomains    56

Making Sense of Bounded Contexts    62

Sample Contexts    72

Wrap-Up    84

Chapter 3: Context Maps    87

Why Context Maps Are So Essential    87

Wrap-Up    111

Chapter 4: Architecture          113

Interviewing the Successful CIO    114

Layers   119

Hexagonal or Ports and Adapters    125

Service-Oriented    130

Representational State Transfer–REST    133

Command-Query Responsibility Segregation, or CQRS    138

Event-Driven Architecture    147

Data Fabric and Grid-Based Distributed Computing    163

Wrap-Up    168

Chapter 5: Entities          171

Why We Use Entities    171

Unique Identity    173

Discovering Entities and Their Intrinsic Characteristics    191

Wrap-Up    217

Chapter 6: Value Objects           219

Value Characteristics    221

Integrate with Minimalism    232

Standard Types Expressed as Values    234

Testing Value Objects    239

Implementation   243

Persisting Value Objects    248

Wrap-Up    263

Chapter 7: Services           265

What a Domain Service Is (but First, What It Is Not)    267

Make Sure You Need a Service    268

Modeling a Service in the Domain    272

Testing Services   281

Wrap-Up    284

Chapter 8: Domain Events           285

The When and Why of Domain Events    285

Modeling Events    288

Publishing Events from the Domain Model    296

Spreading the News to Remote Bounded Contexts    303

Event Store    307

Architectural Styles for Forwarding Stored Events    312

Implementation    318

Wrap-Up    331

Chapter 9: Modules          333

Designing with Modules    333

Basic Module Naming Conventions    336

Module Naming Conventions for the Model    337

Modules of the Agile Project Management Context   340

Modules in Other Layers    343

Module before Bounded Context    344

Wrap-Up    345

Chapter 10: Aggregates          347

Using Aggregates in the Scrum Core Domain    348

Rule: Model True Invariants in Consistency Boundaries    353

Rule: Design Small Aggregates    355

Rule: Reference Other Aggregates by Identity    359

Rule: Use Eventual Consistency Outside the Boundary    364

Reasons to Break the Rules    367

Gaining Insight through Discovery   370

Implementation    380

Wrap-Up   388

Chapter 11: Factories          389

Factories in the Domain Model    389

Factory Method on Aggregate Root    391

Factory on Service   397

Wrap-Up    400

Chapter 12: Repositories          401

Collection-Oriented Repositories    402

Persistence-Oriented Repositories    418

Additional Behavior    430

Managing Transactions   432

Type Hierarchies    437

Repository versus Data Access Object    440

Testing Repositories    441

Wrap-Up    448

Chapter 13: Integrating Bounded Contexts            449

Integration Basics    450

Integration Using RESTful Resources          458

Integration Using Messaging    469

Wrap-Up   508

Chapter 14: Application           509

User Interface     512

Application Services    521

Composing Multiple Bounded Contexts    531

Infrastructure    532

Enterprise Component Containers    534

Wrap-Up    537

Appendix A: Aggregates and Event Sourcing: A+ES   539

Inside an Application Service    541

Command Handlers    549

Lambda Syntax    553

Concurrency Control    554

Structural Freedom with A+ES    558

Performance    558

Implementing an Event Store    561

Relational Persistence    565

BLOB Persistence    568

Focused Aggregates    569

Read Model Projections    570

Use with Aggregate Design   573

Events Enrichment     573

Supporting Tools and Patterns     576

Contract Generation    580

Unit Testing and Specifications    582

Event Sourcing in Functional Languages    583

Sample Pages

Download the sample pages (includes Chapter 10 and Index)