- Preface
- Managing Complexity, Solving Business Problems
- Why Python?
- TDD, DDD and Event-Driven Architecture
- Who Should Read This Book
- A note to our Early Release Readers
- A Brief Overview of What You’ll Learn
- Example Code and Coding Along
- Conventions Used in This Book
- O’Reilly Online Learning
- How to Contact O’Reilly
- Acknowledgments
- Introduction: Why Do Our Designs Go Wrong?
- I. Building an Architecture to Support Domain Modelling
- 1. Domain Modelling
- 2. Repository Pattern
- 3. A Brief Interlude: On Coupling and Abstractions
- 4. Our First Use Case: Flask API and Service Layer
- Connecting Our Application to the Real World
- A First End-To-End (E2E) Test
- The Straightforward Implementation
- Error Conditions That Require Database Checks
- Introducing a Service Layer, and Using FakeRepository to Unit Test It
- Why Is Everything Called A Service?
- Putting things in folders to see where everything belongs
- Wrap-Up
- 5. TDD in High Gear and Low Gear
- 6. Unit of Work Pattern
- The Unit of Work Collaborates with Repository(-Ies)
- Test-Driving a UoW with Integration Tests
- Unit of Work and Its Context Manager
- Fake Unit of Work for Testing:
- Using the UoW in the Service Layer
- Explicit Tests for Commit/Rollback Behavior
- Explicit vs Implicit Commits
- Examples: Using UoW to Group Multiple Operations Into an Atomic Unit
- Tidying Up the Integration Tests
- Wrap-Up
- 7. Aggregates and Consistency Boundaries
- II. Event-Driven Architecture
- 8. Events and the Message Bus
- 9. Going to Town on the Message Bus
- 10. Commands and Command Handler
- 11. Event-Driven Architecture: Using Events to Integrate Microservices
- 12. Command-Query Responsibility Separation (CQRS)
- Domain models are for writing
- Most users aren’t going to buy your furniture
- Post/Redirect/Get and CQS
- Hold on to Your Lunch Folks.
- Testing CQRS Views
- “Obvious” Alternative 1: Using the Existing Repository
- Your Domain Model is not Optimized for Read Operations
- “Obvious” Alternative 2: Using the ORM
- SELECT N+1, and Other Performance Considerations
- Time to completely jump the shark
- Changing our Read Model Implementation is Easy
- But Would You Really? CRUD versus CQRS.
- 13. Dependency Injection (And Bootstrapping)
- Implicit vs Explicit Dependencies
- Aren’t Explicit Dependencies Totally Weird and Java-Ey Tho?
- Preparing Handlers: Manual DI with Closures and Partials
- An Alternative Using Classes
- A Bootstrap Script
- Messagebus Gets Given Handlers at Runtime
- Using Bootstrap in Our Entrypoints
- Initializing DI in Our Tests
- Building an Adapter “Properly”: A Worked Example
- DI and bootstrap wrap-up
- Epilogue: What now?
- How do I get there from here?
- Separating entangled responsibilities
- Identifying Aggregates and Bounded Contexts
- An Event-driven Approach to go Microservices Via Strangler Pattern
- Convincing your stakeholders to try something new
- Getting started
- More required reading
- Questions our Tech Reviewers Asked That We Couldn’t Work Into Prose
- Footguns
- A. Summary diagram and table
- B. A Template Project Structure
- C. Swapping Out the Infrastructure: Do Everything with CSVs
- D. Repository and Unit of Work Patterns with Django
- E. Validation
- Index
About the Authors
Harry Percival spent a few years being deeply unhappy as a management consultant. Soon he rediscovered his true geek nature and was lucky enough to fall in with a bunch of XP fanatics, working on the pioneering the sadly defunct Resolver One spreadsheet. He worked at PythonAnywhere LLP, spreading the gospel of TDD world-wide at talks, workshops and conferences. He is now with MADE.COM.
Bob Gregory is a UK-based software architect with MADE.COM. He has been building event driven systems with domain-driven design for more than a decade.
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