Table of Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii
Part I.
Strategic Design
1. Analyzing Business Domains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
What Is a Business Domain?
What Is a Subdomain?
Types of Subdomains
Comparing Subdomains
Identifying Subdomain Boundaries
Domain Analysis Examples
Gigmaster
BusVNext
Who Are the Domain Experts?
Conclusion
Exercises
3
4
4
7
11
14
14
15
17
18
18
2. Discovering Domain Knowledge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Business Problems
Knowledge Discovery
Communication
What Is a Ubiquitous Language?
Language of the Business
21
22
22
24
25
v
Scenarios
Consistency
Model of the Business Domain
What Is a Model?
Effective Modeling
Modeling the Business Domain
Continuous Effort
Tools
Challenges
Conclusion
Exercises
25
26
27
27
28
28
29
29
30
31
32
3. Managing Domain Complexity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Inconsistent Models
What Is a Bounded Context?
Model Boundaries
Ubiquitous Language Refined
Scope of a Bounded Context
Bounded Contexts Versus Subdomains
Subdomains
Bounded Contexts
The Interplay Between Subdomains and Bounded Contexts
Boundaries
Physical Boundaries
Ownership Boundaries
Bounded Contexts in Real Life
Semantic Domains
Science
Buying a Refrigerator
Conclusion
Exercises
33
35
36
37
37
38
39
39
39
41
41
42
42
43
43
44
46
46
4. Integrating Bounded Contexts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Cooperation
Partnership
Shared Kernel
Customer–Supplier
Conformist
Anticorruption Layer
Open-Host Service
Separate Ways
Communication Issues
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50
50
50
53
53
54
55
56
56
Generic Subdomains
Model Differences
Context Map
Maintenance
Limitations
Conclusion
Exercises
56
56
57
58
58
59
59
Part II. Tactical Design
5. Implementing Simple Business Logic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Transaction Script
Implementation
It’s Not That Easy!
When to Use Transaction Script
Active Record
Implementation
When to Use Active Record
Be Pragmatic
Conclusion
Exercises
63
64
64
68
69
70
71
72
72
72
6. Tackling Complex Business Logic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
History
Domain Model
Implementation
Building Blocks
Managing Complexity
Conclusion
Exercises
75
76
77
77
94
95
96
7. Modeling the Dimension of Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Event Sourcing
Search
Analysis
Source of Truth
Event Store
Event-Sourced Domain Model
Advantages
Disadvantages
Frequently Asked Questions
99
104
105
107
107
108
110
111
112
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Performance
Deleting Data
Why Can’t I Just…?
Conclusion
Exercises
112
114
114
115
116
8. Architectural Patterns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Business Logic Versus Architectural Patterns
Layered Architecture
Presentation Layer
Business Logic Layer
Data Access Layer
Communication Between Layers
Variation
When to Use Layered Architecture
Ports & Adapters
Terminology
Dependency Inversion Principle
Integration of Infrastructural Components
Variants
When to Use Ports & Adapters
Command-Query Responsibility Segregation
Polyglot Modeling
Implementation
Projecting Read Models
Challenges
Model Segregation
When to Use CQRS
Scope
Conclusion
Exercises
117
118
118
119
119
120
121
124
125
126
126
127
128
128
128
129
129
130
132
133
133
134
135
135
9. Communication Patterns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Model Translation
Stateless Model Translation
Stateful Model Translation
Integrating Aggregates
Outbox
Saga
Process Manager
Conclusion
Exercises
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137
138
141
143
145
147
150
154
154
Part III. Applying Domain-Driven Design in Practice
10. Design Heuristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Heuristic
Bounded Contexts
Business Logic Implementation Patterns
Architectural Patterns
Testing Strategy
Testing Pyramid
Testing Diamond
Reversed Testing Pyramid
Tactical Design Decision Tree
Conclusion
Exercises
159
160
161
163
164
165
165
165
166
167
167
11. Evolving Design Decisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Changes in Domains
Core to Generic
Generic to Core
Supporting to Generic
Supporting to Core
Core to Supporting
Generic to Supporting
Strategic Design Concerns
Tactical Design Concerns
Transaction Script to Active Record
Active Record to Domain Model
Domain Model to Event-Sourced Domain Model
Generating Past Transitions
Modeling Migration Events
Organizational Changes
Partnership to Customer–Supplier
Customer–Supplier to Separate Ways
Domain Knowledge
Growth
Subdomains
Bounded Contexts
Aggregates
Conclusion
Exercises
169
170
170
171
171
172
172
172
173
174
174
176
176
177
178
179
179
179
180
180
181
182
182
183
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12. EventStorming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
What Is EventStorming?
Who Should Participate in EventStorming?
What Do You Need for EventStorming?
The EventStorming Process
Step 1: Unstructured Exploration
Step 2: Timelines
Step 3: Pain Points
Step 4: Pivotal Events
Step 5: Commands
Step 6: Policies
Step 7: Read Models
Step 8: External Systems
Step 9: Aggregates
Step 10: Bounded Contexts
Variants
When to Use EventStorming
Facilitation Tips
Watch the Dynamics
Remote EventStorming
Conclusion
Exercises
185
186
186
187
187
188
189
190
190
191
192
193
194
194
195
196
196
197
197
198
198
13. Domain-Driven Design in the Real World. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Strategic Analysis
Understand the Business Domain
Explore the Current Design
Modernization Strategy
Strategic Modernization
Tactical Modernization
Cultivate a Ubiquitous Language
Pragmatic Domain-Driven Design
Selling Domain-Driven Design
Undercover Domain-Driven Design
Conclusion
Exercises
Part IV.
202
202
203
204
205
207
207
210
211
211
213
214
Relationships to Other Methodologies and Patterns
14. Microservices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
What Is a Service?
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What Is a Microservice?
Method as a Service: Perfect Microservices?
Design Goal
System Complexity
Microservices as Deep Services
Microservices as Deep Modules
Domain-Driven Design and Microservices’ Boundaries
Bounded Contexts
Aggregates
Subdomains
Compressing Microservices’ Public Interfaces
Open-Host Service
Anticorruption Layer
Conclusion
Exercises
218
219
220
221
222
223
225
225
227
228
229
229
230
231
232
15. Event-Driven Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Event-Driven Architecture
Events
Events, Commands, and Messages
Structure
Types of Events
Designing Event-Driven Integration
Distributed Big Ball of Mud
Temporal Coupling
Functional Coupling
Implementation Coupling
Refactoring the Event-Driven Integration
Event-Driven Design Heuristics
Conclusion
Exercises
233
234
234
235
236
241
241
242
243
243
243
245
246
247
16. Data Mesh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Analytical Data Model Versus Transactional Data Model
Fact Table
Dimension Table
Analytical Models
Analytical Data Management Platforms
Data Warehouse
Data Lake
Challenges of Data Warehouse and Data Lake Architectures
Data Mesh
249
250
252
253
254
254
257
258
259
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Decompose Data Around Domains
Data as a Product
Enable Autonomy
Build an Ecosystem
Combining Data Mesh and Domain-Driven Design
Conclusion
Exercises
259
261
262
262
263
264
265
Closing Words. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
A. Applying DDD: A Case Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
B. Answers to Exercise Questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
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