Domain Driven Design in .NET 8

Domain-Driven Design (DDD) is a powerful approach to software development that emphasizes collaboration between technical and domain experts to solve complex domain problems. By focusing on the core domain and its logic, developers can create systems that are more aligned with business goals. With the release of .NET 8, implementing DDD has become even more streamlined and efficient. In this article, we will explore how to implement DDD principles in a .NET 8 application with a simple code example.

At its core, DDD is about creating software that reflects the reality of the business domain. It involves several key concepts:

1. Entities: Objects with distinct identities that persist over time.
2. Value Objects: Immutable objects that describe aspects of the domain without having an identity.
3. Aggregates: Clusters of entities and value objects treated as a single unit.
4. Repositories: Abstractions for data access operations.
5. Services: Operations or logic not naturally belonging to entities or value objects.

First, ensure you have the latest version of .NET 8 installed on your machine. You can create a new console application using the following command:

dotnet new console -n DddExample
cd DddExample

Let's start by defining an entity and a value object.

// Value Object
public record Address(string Street, string City, string ZipCode);

// Entity
public class Customer
{
    public Guid Id { get; private set; }
    public string Name { get; private set; }
    public Address Address { get; private set; }

    public Customer(Guid id, string name, Address address)
    {
        Id = id;
        Name = name;
        Address = address;
    }

    public void UpdateAddress(Address newAddress)
    {
        Address = newAddress;
    }
}

In this example, Address is defined as a record type in C#, making it immutable by default — ideal for a value object. The Customer class represents an entity with an identity (Id) and has behavior associated with it (e.g., updating the address).

The Customer entity could serve as an aggregate root if it encapsulates related entities or value objects.

public class OrderItem
{
    public Guid ProductId { get; private set; }
    public int Quantity { get; private set; }

    public OrderItem(Guid productId, int quantity)
    {
        ProductId = productId;
        Quantity = quantity;
    }
}

public class Order : IAggregateRoot
{
    public Guid Id { get; private set; }
    public Customer Customer { get; private set; }
    public List<OrderItem> Items { get; private set; } = new();

    public Order(Guid id, Customer customer)
    {
        Id = id;
        Customer = customer;
    }

    public void AddOrderItem(OrderItem item)
    {
        Items.Add(item);
    }
}

Here, Order acts as an aggregate root containing OrderItems.

Repositories abstract data access logic from business logic.

public interface IOrderRepository
{
    void Add(Order order);
    
	// Other methods like GetById(), Remove(), etc.
}

public class InMemoryOrderRepository : IOrderRepository
{
	// Simple in-memory storage for demonstration purposes.
	private readonly List<Order> _orders = new();

	public void Add(Order order)
	{
		_orders.Add(order);
	}

	// Additional methods would go here...
}

This interface defines basic CRUD operations related to orders.

Here's how you might use these components in your application:

class Program
{
	static void Main()
	{
		var customer = new Customer(Guid.NewGuid(), "Alice Johnson", new Address("123 Elm St", "Wonderland", "12345"));
		
		var orderRepository = new InMemoryOrderRepository();
		
		var order = new Order(Guid.NewGuid(), customer);
		order.AddOrderItem(new OrderItem(Guid.NewGuid(), 2));
		
		orderRepository.Add(order);

		Console.WriteLine("Order added successfully");
		
	    // Further operations can be performed here...
	}
}

Implementing Domain-Driven Design in .NET 8 allows developers to build systems closely aligned with business objectives while maintaining clean architecture principles. This simple example demonstrates how you can define entities, value objects, aggregates, and repositories to structure your application effectively using DDD principles.

As you advance further into DDD within .NET 8 applications, consider exploring bounded contexts and domain events for even more rigorous alignment between your codebase and business needs. Happy coding!