Bits of .NET

🎯 Key Takeaways: Clean, type-safe configuration binding with validation, reloading, and dependency injection. The definitive guide to IOptions, IOptionsSnapshot, and IOptionsMonitor.

Using strings and magic values in your code? The Options Pattern brings type-safety and flexibility to your configuration.

📦 Basic Setup

// appsettings.json
{
  "EmailSettings": {
    "SmtpServer": "smtp.gmail.com",
    "SmtpPort": 587,
    "SenderEmail": "noreply@myapp.com",
    "SenderName": "MyApp",
    "EnableSsl": true,
    "MaxRetries": 3
  }
}

// Model
public class EmailSettings
{
    public string SmtpServer { get; set; } = string.Empty;
    public int SmtpPort { get; set; }
    public string SenderEmail { get; set; } = string.Empty;
    public string SenderName { get; set; } = string.Empty;
    public bool EnableSsl { get; set; }
    public int MaxRetries { get; set; }
}

// Registration
builder.Services.Configure<EmailSettings>(
    builder.Configuration.GetSection("EmailSettings"));

🔄 Three Options Types

// 1. IOptions<T> - Singleton (static after startup)
public class EmailService
{
    private readonly EmailSettings _settings;
    public EmailService(IOptions<EmailSettings> options)
    {
        _settings = options.Value; // ✅ Single snapshot
    }
}

// 2. IOptionsSnapshot<T> - Scoped (reloads on change)
public class EmailService
{
    private readonly IOptionsSnapshot<EmailSettings> _options;
    public EmailService(IOptionsSnapshot<EmailSettings> options)
    {
        _options = options; // ✅ Fresh each time
    }
    public void SendEmail()
    {
        var settings = _options.Value; // ✅ Reloaded per request
    }
}

// 3. IOptionsMonitor<T> - Singleton (auto-reloads, change notifications)
public class EmailService
{
    private readonly IOptionsMonitor<EmailSettings> _monitor;
    private readonly IDisposable? _changeListener;
    
    public EmailService(IOptionsMonitor<EmailSettings> monitor)
    {
        _monitor = monitor;
        _changeListener = _monitor.OnChange(settings =>
        {
            Console.WriteLine("Email config changed!");
            // React to changes
        });
    }
}

✅ Validation

// With validation
public class EmailSettings
{
    [Required]
    [MinLength(5)]
    public string SmtpServer { get; set; } = string.Empty;
[Range(1, 65535)]
public int SmtpPort { get; set; }

[EmailAddress]
public string SenderEmail { get; set; } = string.Empty;

[Required]
public string SenderName { get; set; } = string.Empty;

[Range(1, 10)]
public int MaxRetries { get; set; }
}

// Validate on startup
builder.Services.AddOptions<EmailSettings>()
.Bind(builder.Configuration.GetSection("EmailSettings"))
.ValidateDataAnnotations()
.Validate(settings => settings.SmtpPort != 25, "SmtpPort cannot be 25(unsecure)")
.ValidateOnStart();

// 🔥 Throws exception if config is invalid!

💡 Pro Tip: Environment – Specific Config

// appsettings.Development.json
{
"EmailSettings": {
"SmtpServer": "localhost",
"SmtpPort": 1025,
"MaxRetries": 1
}
}

// appsettings.Production.json
{
"EmailSettings": {
"SmtpServer": "smtp.sendgrid.net",
"SmtpPort": 587,
"MaxRetries": 5
}
}

// 💡 Automatic based on ASPNETCORE_ENVIRONMENT