Applying Domain-Driven Design in an Invoice Repository Migration: A Practical Summary

Background – Domain‑Driven Design (DDD) is a systematic approach to software design that clarifies thinking, standardizes processes, reduces complexity, and creates a shared language among team members. The e‑commerce middle‑platform team at AutoHome adopted DDD for the migration of a car‑purchase invoice repository.

DDD Core Concepts – DDD limits problem scope within bounded contexts, defines domains and sub‑domains (core, supporting, generic), and emphasizes a ubiquitous language. Key building blocks include entities, value objects, aggregate roots, domain events, factories, and repositories, with a focus on strong consistency within aggregates and eventual consistency across them.

Practice Process – The migration was carried out in two stages: strategic design (business abstraction and domain modeling) and tactical design (system architecture and implementation). Strategic design used event‑storming to identify aggregates, entities, value objects, and domain events for the invoice domain.

Strategic Design Outcome – The team defined a single aggregate “Invoice” (also the aggregate root) with entities such as duplicate‑check rules and invoice logs, and value objects like audit status, business type, storage type, and application identifier. A repository interface abstracts persistence.

Tactical Design – The implementation followed a four‑layer DDD architecture (presentation, application, domain, infrastructure) and leveraged the COLA framework. Modules include:

Invoice‑ddd‑starter: SpringBoot entry point and controller layer, handling API exposure and DTO‑entity conversion.

Invoice‑ddd‑app: Application layer providing domain services, event bus handling, and MQ integration.

Invoice‑ddd‑domain: Domain layer defining entities, value objects, events, services, and repository interfaces; includes factories and transaction control.

Invoice‑ddd‑infrastructure: Infrastructure layer implementing repositories, event bus, encryption utilities, etc.

Invoice‑ddd‑client: Client module exposing API definitions and DTO/VO classes.

Standardization – To maintain architectural consistency, the team established naming conventions for packages, classes (self‑descriptive, single‑responsibility), and methods, and emphasized the importance of a unified language across the project.

Summary and Benefits – The DDD‑driven migration resulted in clearer system boundaries, faster consensus through a ubiquitous language, a more robust and maintainable codebase (favoring rich‑model over anemic models), and improved extensibility for future features. The team also reflected on common DDD questions such as where to place business logic, transaction scope, and suitable application scenarios.

Overall, the practical experience demonstrates how DDD can elevate the quality and scalability of backend systems when applied thoughtfully.