Chapter 5: Implementing Domain Logic

To communicate effectively, the code must be based on the same language used to write the requirements – the same language that the developers speak with each other and with domain experts.

– Eric Evans

In the Command Query Responsibility Segregation (CQRS) section of the book, we described how DDD and CQRS complement each other and how the command side (write requests) is the home of business logic. In this chapter, we will implement the command-side API for the Letter of Credit (LC) application using Spring Boot, Axon Framework, JSR-303 bean validations, and persistence options by contrasting between state-stored and event-sourced aggregates. The list of topics to be covered is as follows:

• Identifying aggregates
• Handling commands and emitting events
• Test-driving the application
• Persisting aggregates
• Performing validations

By the end of this chapter, you will have learned how to implement the core...