DDD Factories and Services

1. Introduction

Domain-Driven Design (DDD) emphasizes the importance of the domain model in software architecture. Factories and services are key design patterns in DDD that help manage the complexity of creating domain objects and encapsulating business logic.

2. Factories

Factories are responsible for creating instances of domain objects. They encapsulate the instantiation logic, promoting separation of concerns and ensuring that domain objects are created in a consistent manner.

2.1 Definition

In DDD, a factory is a design pattern that provides an interface for creating objects without exposing the instantiation logic to the client.

2.2 Types of Factories

• Simple Factories
• Factory Method
• Abstract Factory

2.3 Example

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

class UserFactory {
    static createUser(name, email) {
        return new User(name, email);
    }
}

// Usage
const user = UserFactory.createUser('John Doe', 'john@example.com');
                

3. Services

Services in DDD are used to encapsulate domain logic that does not naturally fit within an entity or value object. They provide a way to implement business operations that involve multiple domain objects.

3.1 Definition

A service is an interface or class that provides functionality to the domain layer. It can be used to perform operations that involve one or more entities.

3.2 Types of Services

• Domain Services
• Application Services

3.3 Example

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

    registerUser(name, email) {
        const user = UserFactory.createUser(name, email);
        this.userRepository.save(user);
    }
}

// Usage
const userService = new UserService(userRepository);
userService.registerUser('Jane Doe', 'jane@example.com');
                

4. Best Practices

To effectively use factories and services in DDD, consider the following best practices:

1. Keep factories focused on object creation only.
2. Encapsulate business logic within services.
3. Avoid using services for simple getters/setters.
4. Utilize dependency injection for better testability.

5. FAQ