Domain-Driven Design in Node.js

Introduction

Domain-Driven Design (DDD) is an approach to software development that emphasizes collaboration between technical experts and domain experts to model and develop complex software systems. In this lesson, we will explore how to implement DDD in Node.js applications.

Core Concepts

1. Domain

The domain is the problem space for which you are building software. It includes all relevant business logic.

2. Ubiquitous Language

A common language derived from the domain model that is used by both developers and non-developers.

3. Bounded Context

A defined boundary within which a particular model is applicable. Different models can exist in different bounded contexts.

4. Entities and Value Objects

Entities are objects with a distinct identity, whereas value objects are objects defined by their attributes.

Implementing DDD

Below is a step-by-step guide to implementing DDD in a Node.js application:

Step 1: Define Your Domain Model


class User {
    constructor(id, name, email) {
        this.id = id;
        this.name = name;
        this.email = email;
    }
}

Step 2: Create Value Objects


class Email {
    constructor(email) {
        this.email = email;
    }

    validate() {
        // Email validation logic
    }
}

Step 3: Define Repositories


class UserRepository {
    constructor() {
        this.users = new Map();
    }

    save(user) {
        this.users.set(user.id, user);
    }

    findById(id) {
        return this.users.get(id);
    }
}

Step 4: Create Services


class UserService {
    constructor(userRepository) {
        this.userRepository = userRepository;
    }

    registerUser(name, email) {
        const user = new User(Date.now(), name, email);
        this.userRepository.save(user);
        return user;
    }
}

Best Practices

Note: Always focus on the domain, and avoid getting caught up in technical details.

Collaborate with domain experts regularly.
Use a consistent and clear language throughout the application.
Keep bounded contexts well-defined and avoid overlaps.
Ensure that entities and value objects are immutable where possible.
Refactor regularly to keep the model aligned with the business.

FAQ

What is Domain-Driven Design?

Domain-Driven Design is a software development approach that focuses on modeling software based on the core domain and its logic.

Why use DDD in Node.js?

Node.js allows you to build scalable applications, and DDD helps in managing complex business logic effectively.

What is a Bounded Context?

A bounded context is a boundary within which a particular domain model is defined and applicable.