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Domain-Driven Design with Java - A Practitioner's Guide

You're reading from   Domain-Driven Design with Java - A Practitioner's Guide Create simple, elegant, and valuable software solutions for complex business problems

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Product type Paperback
Published in Aug 2022
Publisher Packt
ISBN-13 9781800560734
Length 302 pages
Edition 1st Edition
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Authors (2):
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Karthik Krishnan Karthik Krishnan
Author Profile Icon Karthik Krishnan
Karthik Krishnan
Premanand Chandrasekaran Premanand Chandrasekaran
Author Profile Icon Premanand Chandrasekaran
Premanand Chandrasekaran
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Table of Contents (17) Chapters Close

Preface 1. Part 1: Foundations
2. Chapter 1: The Rationale for Domain-Driven Design FREE CHAPTER 3. Chapter 2: Where and How Does DDD Fit? 4. Part 2: Real-World DDD
5. Chapter 3: Understanding the Domain 6. Chapter 4: Domain Analysis and Modeling 7. Chapter 5: Implementing Domain Logic 8. Chapter 6: Implementing the User Interface – Task-Based 9. Chapter 7: Implementing Queries 10. Chapter 8: Implementing Long-Running Workflows 11. Chapter 9: Integrating with External Systems 12. Part 3: Evolution Patterns
13. Chapter 10: Beginning the Decomposition Journey 14. Chapter 11: Decomposing into Finer-Grained Components 15. Chapter 12: Beyond Functional Requirements 16. Other Books You May Enjoy

Implementing the query side

In Chapter 5, Implementing Domain Logic, we examined how to publish events when a command is successfully processed. Now, let’s look at how we can construct a query model by listening to these domain events. Logically, this will look something like the following diagram:

Figure 7.2 – The CQRS application – the query side

For a detailed explanation of how the command side is implemented, please refer to the Implementing the command side section in Chapter 5, Implementing Domain Logic.

The high-level sequence on the query side is described here:

  1. An event listening component listens to these domain events published on the event bus.
  2. It constructs a purpose-built query model to satisfy a specific query use case.
  3. This query model is persisted in a datastore optimized for read operations.
  4. This query model is then exposed in the form of an API.

Note how there can exist more than one query...

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