Vivek Kaushik

What is the Options Pattern?

The Options pattern is a design pattern in .NET primarily used to represent groups of related configuration settings as strongly-typed classes. Instead of directly accessing configuration values as strings or loosely typed data, this pattern provides a way to bind configuration sections (from files like appsettings.json, environment variables, or other sources) to POCO (Plain Old CLR Objects) classes. These classes can then be injected into your components via dependency injection using the IOptions<T> interface.

By using the Options pattern, configuration values become safer, easier to manage, and maintain, especially when dealing with complex or hierarchical configurations.

Why use the Options Pattern?

Strongly-typed configuration access:

Instead of accessing configuration values by raw strings, you get type safety and IntelliSense support in your IDE. This reduces errors such as typos.

Improved maintainability and readability:

Grouping related configuration values into classes reflects domain concepts and makes configuration management more organized.

Dependency Injection friendly:

Options classes can be injected where needed through IOptions<T>, IOptionsSnapshot<T>, or IOptionsMonitor<T>, promoting clean separation of concerns and easier unit testing.

Support for configuration validation:

You can validate configuration data at startup by implementing validation logic on options classes, catching configuration errors early.

Support for reloadable configurations:

With IOptionsSnapshot<T> or IOptionsMonitor<T>, your app can respond to configuration changes at runtime, which is useful for dynamic settings.

Flexibility in configuration sources:

Options pattern works seamlessly with multiple configuration providers (appsettings.json, environment variables, command line args), following .NET’s layered configuration model.

How to use the Options Pattern?

Step 1: Define your Options class

Create a simple POCO class matching the structure of your config section.

Example appsettings.json section:


{
  "WeatherOptions": {
    "ApiKey": "12345",
    "City": "Seattle",
    "Units": "Metric"
  }
}

C# class:


public class WeatherOptions
{
    public string ApiKey { get; set; }
    public string City { get; set; }
    public string Units { get; set; }
}

Step 2: Register the Options class with the DI container

Bind the config section to your options class in Program.cs (or Startup.cs in older projects):


var builder = WebApplication.CreateBuilder(args);

builder.Services.Configure<WeatherOptions>(
    builder.Configuration.GetSection("WeatherOptions"));

var app = builder.Build();

This binds the WeatherOptions section in configuration to the WeatherOptions class and registers it with the dependency injection system.

Step 3: Inject and use the Options in your classes

Inject IOptions<T> (or related interfaces) in the constructor to access the configuration values:


using Microsoft.Extensions.Options;

public class WeatherService
{
    private readonly WeatherOptions _options;

    public WeatherService(IOptions<WeatherOptions> options)
    {
        _options = options.Value; // Values are accessed here
    }

    public void DisplayWeatherConfig()
    {
        Console.WriteLine($"API Key: {_options.ApiKey}");
        Console.WriteLine($"City: {_options.City}");
        Console.WriteLine($"Units: {_options.Units}");
    }
}

Variants for options injection:

IOptions<T>: Provides a singleton snapshot of the configuration at application start (does not track changes after startup).

IOptionsSnapshot<T>: Scoped service that provides configuration snapshots that update per request in web apps (helps track config changes without restarting).

IOptionsMonitor<T>: Singleton service that can listen for configuration reloads and notify consumers in real-time.

Additional Features:

Validation: Add validation logic by implementing IValidateOptions<T> or using the Validate() extension during service registration.

Default values: You can set defaults in your options class constructors or during binding.

Support for nested hierarchical configuration: Options classes can be composed to reflect nested JSON or hierarchical config structures.

Summary

Aspect	Description
Purpose	Strongly-typed binding of configuration settings in .NET applications
Benefits	Type-safety, maintainability, DI integration, validation, runtime reload support
Usage	Define POCO class, bind config section using `Configure<T>()`, inject `IOptions<T>` or variants
Configuration sources	Works with appsettings.json, environment variables, command line args, etc.
Runtime updates	Use `IOptionsSnapshot<T>` or `IOptionsMonitor<T>` for dynamic config changes