Implementing Domain-Driven Design

Contents......Page 10
Foreword......Page 18
Preface......Page 20
Acknowledgments......Page 30
About the Author......Page 34
Guide to This Book......Page 36
Chapter 1 Getting Started with DDD......Page 44
Can I DDD?......Page 45
Why You Should Do DDD......Page 49
How to Do DDD......Page 63
The Business Value of Using DDD......Page 68
1. The Organization Gains a Useful Model of Its Domain......Page 69
4. A Better User Experience Is Gained......Page 70
8. New Tools, Both Strategic and Tactical, Are Employed......Page 71
The Challenges of Applying DDD......Page 72
Fiction, with Bucketfuls of Reality......Page 81
Wrap-Up......Page 84
Big Picture......Page 86
Subdomains and Bounded Contexts at Work......Page 87
Focus on the Core Domain......Page 93
Why Strategic Design Is So Incredibly Essential......Page 96
Real-World Domains and Subdomains......Page 99
Making Sense of Bounded Contexts......Page 105
Room for More than the Model......Page 109
Size of Bounded Contexts......Page 111
Aligning with Technical Components......Page 114
Sample Contexts......Page 115
Collaboration Context......Page 116
Identity and Access Context......Page 123
Agile Project Management Context......Page 125
Wrap-Up......Page 127
Why Context Maps Are So Essential......Page 130
Drawing Context Maps......Page 132
Projects and Organizational Relationships......Page 134
Mapping the Three Contexts......Page 138
Wrap-Up......Page 154
Chapter 4 Architecture......Page 156
Interviewing the Successful CIO......Page 157
Layers......Page 162
Dependency Inversion Principle......Page 166
Hexagonal or Ports and Adapters......Page 168
Service-Oriented......Page 173
REST as an Architectural Style......Page 176
Key Aspects of a RESTful HTTP Server......Page 178
REST and DDD......Page 179
Command-Query Responsibility Segregation, or CQRS......Page 181
Examining Areas of CQRS......Page 183
Dealing with an Eventually Consistent Query Model......Page 189
Event-Driven Architecture......Page 190
Pipes and Filters......Page 192
Long-Running Processes, aka Sagas......Page 196
Event Sourcing......Page 203
Data Fabric and Grid-Based Distributed Computing......Page 206
Data Replication......Page 207
Event-Driven Fabrics and Domain Events......Page 208
Continuous Queries......Page 209
Distributed Processing......Page 210
Wrap-Up......Page 211
Why We Use Entities......Page 214
Unique Identity......Page 216
User Provides Identity......Page 217
Application Generates Identity......Page 218
Persistence Mechanism Generates Identity......Page 222
Another Bounded Context Assigns Identity......Page 225
When the Timing of Identity Generation Matters......Page 227
Surrogate Identity......Page 229
Identity Stability......Page 231
Discovering Entities and Their Intrinsic Characteristics......Page 234
Uncovering Entities and Properties......Page 235
Digging for Essential Behavior......Page 239
Roles and Responsibilities......Page 243
Construction......Page 248
Validation......Page 251
Change Tracking......Page 259
Wrap-Up......Page 260
Chapter 6 Value Objects......Page 262
Immutable......Page 264
Conceptual Whole......Page 266
Replaceability......Page 269
Value Equality......Page 270
Side-Effect-Free Behavior......Page 271
Integrate with Minimalism......Page 275
Standard Types Expressed as Values......Page 277
Testing Value Objects......Page 282
Implementation......Page 286
Persisting Value Objects......Page 291
Reject Undue Influence of Data Model Leakage......Page 292
ORM and Single Value Objects......Page 294
ORM and Many Values Serialized into a Single Column......Page 296
ORM and Many Values Backed by a Database Entity......Page 298
ORM and Many Values Backed by a Join Table......Page 303
ORM and Enum-as-State Objects......Page 304
Wrap-Up......Page 306
Chapter 7 Services......Page 308
What a Domain Service Is (but First, What It Is Not)......Page 310
Make Sure You Need a Service......Page 311
Modeling a Service in the Domain......Page 315
Is Separated Interface a Necessity?......Page 318
A Calculation Process......Page 320
Transformation Services......Page 323
Testing Services......Page 324
Wrap-Up......Page 327
The When and Why of Domain Events......Page 328
Modeling Events......Page 331
With Aggregate Characteristics......Page 337
Identity......Page 338
Publishing Events from the Domain Model......Page 339
Publisher......Page 340
Subscribers......Page 343
Messaging Infrastructure Consistency......Page 346
Autonomous Services and Systems......Page 348
Latency Tolerances......Page 349
Event Store......Page 350
Publishing Notifications as RESTful Resources......Page 355
Publishing Notifications through Messaging Middleware......Page 360
Implementation......Page 361
Publishing the NotificationLog......Page 362
Publishing Message-Based Notifications......Page 367
Wrap-Up......Page 374
Designing with Modules......Page 376
Basic Module Naming Conventions......Page 379
Module Naming Conventions for the Model......Page 380
Modules of the Agile Project Management Context......Page 383
Modules in Other Layers......Page 386
Module before Bounded Context......Page 387
Wrap-Up......Page 388
Chapter 10 Aggregates......Page 390
Using Aggregates in the Scrum Core Domain......Page 391
First Attempt: Large-Cluster Aggregate......Page 392
Second Attempt: Multiple Aggregates......Page 394
Rule: Model True Invariants in Consistency Boundaries......Page 396
Rule: Design Small Aggregates......Page 398
Don?t Trust Every Use Case......Page 401
Rule: Reference Other Aggregates by Identity......Page 402
Making Aggregates Work Together through Identity References......Page 404
Model Navigation......Page 405
Scalability and Distribution......Page 406
Rule: Use Eventual Consistency Outside the Boundary......Page 407
Ask Whose Job It Is......Page 409
Reason One: User Interface Convenience......Page 410
Reason Two: Lack of Technical Mechanisms......Page 411
Reason Four: Query Performance......Page 412
Rethinking the Design, Again......Page 413
Estimating Aggregate Cost......Page 415
Common Usage Scenarios......Page 416
Memory Consumption......Page 417
Exploring Another Alternative Design......Page 418
Implementing Eventual Consistency......Page 419
Is It the Team Member?s Job?......Page 421
Time for Decisions......Page 422
Create a Root Entity with Unique Identity......Page 423
Using Law of Demeter and Tell, Don?t Ask......Page 425
Optimistic Concurrency......Page 428
Avoid Dependency Injection......Page 430
Wrap-Up......Page 431
Factories in the Domain Model......Page 432
Factory Method on Aggregate Root......Page 434
Creating CalendarEntry Instances......Page 435
Creating Discussion Instances......Page 438
Factory on Service......Page 440
Wrap-Up......Page 443
Chapter 12 Repositories......Page 444
Collection-Oriented Repositories......Page 445
Hibernate Implementation......Page 450
Considerations for a TopLink Implementation......Page 459
Persistence-Oriented Repositories......Page 461
Coherence Implementation......Page 463
MongoDB Implementation......Page 468
Additional Behavior......Page 473
Managing Transactions......Page 475
Type Hierarchies......Page 480
Repository versus Data Access Object......Page 483
Testing Repositories......Page 484
Testing with In-Memory Implementations......Page 488
Wrap-Up......Page 491
Chapter 13 Integrating Bounded Contexts......Page 492
Integration Basics......Page 493
Distributed Systems Are Fundamentally Different......Page 494
Exchanging Information across System Boundaries......Page 495
Integration Using RESTful Resources......Page 501
Implementing the RESTful Resource......Page 502
Implementing the REST Client Using an Anticorruption Layer......Page 506
Staying Informed about Product Owners and Team Members......Page 512
Can You Handle the Responsibility?......Page 519
Long-Running Processes, and Avoiding Responsibility......Page 524
Process State Machines and Time-out Trackers......Page 536
Designing a More Sophisticated Process......Page 546
When Messaging or Your System Is Unavailable......Page 550
Wrap-Up......Page 551
Chapter 14 Application......Page 552
Rendering Domain Objects......Page 555
Render Data Transfer Object from Aggregate Instances......Page 556
Use a Mediator to Publish Aggregate Internal State......Page 557
Render Aggregate Instances from a Domain Payload Object......Page 558
State Representations of Aggregate Instances......Page 559
Dealing with Multiple, Disparate Clients......Page 560
Rendition Adapters and Handling User Edits......Page 561
Application Services......Page 564
Sample Application Service......Page 565
Decoupled Service Output......Page 571
Composing Multiple Bounded Contexts......Page 574
Infrastructure......Page 575
Enterprise Component Containers......Page 577
Wrap-Up......Page 580
Appendix A: Aggregates and Event Sourcing: A+ES......Page 582
Inside an Application Service......Page 584
Command Handlers......Page 592
Lambda Syntax......Page 596
Concurrency Control......Page 597
Performance......Page 601
Implementing an Event Store......Page 604
Relational Persistence......Page 608
BLOB Persistence......Page 611
Focused Aggregates......Page 612
Read Model Projections......Page 613
Events Enrichment......Page 616
Event Serializers......Page 619
Value Objects......Page 620
Contract Generation......Page 623
Unit Testing and Specifications......Page 625
Event Sourcing in Functional Languages......Page 626
Bibliography......Page 628
A......Page 632
B......Page 634
C......Page 635
D......Page 638
E......Page 640
G......Page 642
I......Page 643
M......Page 645
P......Page 647
Q......Page 648
R......Page 649
S......Page 650
T......Page 652
U......Page 653
V......Page 654
Z......Page 655