/src
├── MyApp.Api          // Minimal API hoặc MVC
├── MyApp.Application  // Use cases: CQRS, DTOs
├── MyApp.Domain       // Quy tắc nghiệp vụ: Entities, Enums, Interfaces
├── MyApp.Infrastructure // EF Core, Services, External APIs
└── MyApp.Tests        // Unit & Integration Tests

public record CreateOrderCommand(string CustomerId) : IRequest<Guid>;

public class CreateOrderHandler : IRequestHandler<CreateOrderCommand, Guid>
{
    public async Task<Guid> Handle(CreateOrderCommand cmd, CancellationToken ct)
    {
        var order = new Order(cmd.CustomerId);
        _db.Orders.Add(order);
        await _db.SaveChangesAsync(ct);
        return order.Id;
    }
}

// Trong Domain hoặc Application
public interface IEmailSender
{
    Task SendAsync(string to, string subject, string body);
}

// Trong Infrastructure
public class SendGridEmailSender : IEmailSender
{
    public Task SendAsync(string to, string subject, string body) => /* gửi mail */;
}

public class Order
{
    private readonly List<OrderItem> _items = new();
    public IReadOnlyList<OrderItem> Items => _items.AsReadOnly();

    public void AddItem(Product product, int qty)
    {
        if (qty <= 0) throw new ArgumentException("Số lượng phải lớn hơn 0");
        _items.Add(new OrderItem(product, qty));
    }
}

app.MapPost("/orders", async (CreateOrderCommand cmd, ISender mediator) =>
{
    var id = await mediator.Send(cmd);
    return Results.Created($"/orders/{id}", new { id });
});