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Home Forums How would you design a loosely coupled system using .NET? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 17 Jun 2025
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Designing a loosely coupled system in .NET means building components that are independent and interact through abstractions. 

1. Use Interfaces (Abstraction over Implementation)

Why? It allows code to depend on "what something does" rather than "how it does it."

public interface IEmailService
{
    void Send(string to, string subject, string body);
}

public class SmtpEmailService : IEmailService
{
    public void Send(string to, string subject, string body)
    {
        // SMTP implementation
    }
}

Use the interface in your application code:

public class UserService
{
    private readonly IEmailService _emailService;

    public UserService(IEmailService emailService)
    {
        _emailService = emailService;
    }

    public void Register(string email)
    {
        // business logic
        _emailService.Send(email, "Welcome", "Thanks for registering!");
    }
}

2. Use Dependency Injection (DI)

.NET Core has built-in DI. It helps you inject dependencies rather than hardcoding them.

builder.Services.AddScoped<IEmailService, SmtpEmailService>();
builder.Services.AddScoped<UserService>();

Now the framework handles creation and wiring.

3. Apply SOLID Principles

  • Single Responsibility: one class, one job
  • Open/Closed: extend behavior via interfaces, don’t modify core logic
  • Liskov: interfaces should be substitutable
  • Interface Segregation: smaller, role-specific interfaces
  • Dependency Inversion: high-level modules depend on abstractions

4. Use MediatR (CQRS, Clean Architecture)

Helps decouple layers using mediator pattern. Instead of directly calling services, use requests:

public class CreateUserCommand : IRequest<bool>
{
    public string Email { get; set; }
}

public class CreateUserHandler : IRequestHandler<CreateUserCommand, bool>
{
    private readonly IEmailService _emailService;

    public CreateUserHandler(IEmailService emailService)
    {
        _emailService = emailService;
    }

    public Task<bool> Handle(CreateUserCommand request, CancellationToken cancellationToken)
    {
        _emailService.Send(request.Email, "Welcome", "Thanks!");
        return Task.FromResult(true);
    }
}

5. Service-Oriented or Microservices Architecture

Split the system into independently deployable services that communicate via HTTP, gRPC, or messaging (e.g., RabbitMQ).

6. Use Events or Message Queues for Decoupled Communication

For example, publish an event instead of directly calling a method:

public class UserCreatedEvent
{
    public string Email { get; set; }
}

A background service can listen and act on it, without the source knowing who listens.

7. Avoid Static Dependencies and Tight Coupling

Don't do this:

var emailService = new SmtpEmailService(); // tight coupling

Do this:

private readonly IEmailService _emailService; // via constructor

Summary

Technique Benefit
Interfaces + DI Swappable implementations
SOLID Principles Clear boundaries, easier refactoring
MediatR + CQRS Layer separation, no direct coupling
Messaging (Event bus) Async, scalable decoupling
Microservices Physical separation of concerns
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