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Domain Driven Design

· 2 min read
Sanjeev Sarda
Sanjeev Sarda
High End Engineering

Pioneered by Eric Evans and introduced to the world in his book “Domain-Driven Design: Tackling Complexity in the Heart of Software.”, Domain Driven Design or DDD is a design technique for software systems.

DDD

Core Elements of DDD​

The Ubiquitous Language​

A common shared language used by everyone, whether they're technical or non-technical. We talk about things in the same way in order to communicate with precision and clarity, not because we enjoy looking like comic book guy ;-)

Comic book guy

"Worst blog...ever"

Bounded Contexts​

We use decomposition to break up a complex domain into sub-domains with clear boundaries so each sub-domain can have it's own rules and ubiquitous language if needed. We can communicate and interact across boundaries using well defined APIs or events.

Entities​

Object's which are defined by their identity

Value Objects​

The attributes of a value object are what define it. Usually Immutable.

Aggregates​

We can use composition to create aggregates of related entities and value objects. The class we compose these related items into is typically referred to as the aggregate root.

Repositories​

This is what we call our persistence abstraction.

Domain Services​

Large chunks of logic related to our domain that can involve the interaction of multiple objects.

Factories​

Creational design patterns for encapsulation and valid construction.

Domain Events​

Events related to the domain e.g. New order event, market state changed event.

Anti-Corruption Layer​

Translational layer between bounded contexts, external and legacy systems. The idea is to prevent pollution between your nice clean DDD code and legacy systems which may also use a different ubiquitous language if any.

Benefits of using DDD​

  • Seperation of business logic from infrastructure code
  • Code should reflect the business domain
  • Bounded contexts can grow independently so are less coupled

https://martinfowler.com/bliki/DomainDrivenDesign.html - Martin Fowler on DDD

https://www.youtube.com/watch?v=lrSB9gEUJEQ - DDD and LLMs