Options Pattern In .NET 6.0

In this tutorial, we are going to cover an approach through which we can read the configuration data in .NET Core - the options pattern.

Why the Options Pattern?

Options pattern gives the below features

It can be used to bind configuration data to strongly typed objects.
It adheres to two important software engineering principles - Encapsulation and Separation of Concerns.
It provides a mechanism to validate configuration data.

Please refer to the Microsoft documentation for more details.

Tools which I have used for this tutorial:

Visual Studio 2022 Community Edition – Preview version 17.4 (Preview 2)
.NET 6.0
Web API
Swagger

To begin with, let us create a sample project. The source code can be downloaded from GitHub.

Let us assume that we have the below configuration in appsettings.json

"OptionsTutorial": {
    "InterfaceName" : "IOptions"
}

Create the following class:

public class OptionsTutorial
{
    public const string Position = "OptionsTutorial";
    public string InterfaceName { get; set; }
}

Rules which need to be followed to create this class:

Must be non-abstract with a public parameterless constructor.
All public read-write properties of the type are bound.
Fields are not bound. In the preceding code, “Position” is not bound.
The “Position” field is used so the string " OptionsTutorial " doesn't need to be hard coded in the app when binding the class to a configuration provider.

Bind the configuration data to strongly typed objects.

In Program.cs class, we need to add the below line to bind the configuration data.

builder.Services
    .Configure< OptionsTutorial>(builder.Configuration.GetSection(OptionsTutorial.Position));

Use IOptions<T> Interface

This interface is registered as a Singleton and can be injected into any service lifetime.

This does not support:

Read configuration data after the application has started.
Named Options - Refer to the Microsoft documentation for more details.

Let us make a few code changes in WeatherForecastController.cs

Add the below variable at the beginning of the class.

private OptionsTutorial _optionsTutorial;

make the below code changes in Constructor.

public WeatherForecastController(ILogger<WeatherForecastController> logger, IOptions<OptionsTutorial> options)
{
    _logger = logger;
    this._optionsTutorial = options.Value;
}

Introduce a new action method as below

[HttpGet]
[Route("optionspattern")]
public IActionResult OptionsPattern()
{
    var interfaceName = this._optionsTutorial.InterfaceName;
    var message = $"interface name from OptionsTutorial - {interfaceName}";
    return Ok(message);
}

Let us debug the action method and the result.

Options Pattern in .NET 6.0

We can see that; the configuration data has been bound to the strongly typed object.

Use IOptionsSnapshot<T> Interface

This interface is useful in scenarios where options need to be recomputed on every request. Please refer to the Microsoft documentation for more details on this.
This interface has been registered as Scoped; hence it cannot be injected into Singleton Services.
It supports Names Options.

Add the below settings in Appsettings.json

"SnapShot": {
    "InterfaceName": "IOptionsSnapshot"
}

Add the below interface and classes

public class SnapShot
{
    public const string Position = "Snapshot";
    public string InterfaceName { get; set; }
}

I have created two interfaces - ISnapShotCheckWithScope.cs and ISnapShotCheckWithSingleton.cs for validating the Singleton as well as Scoped service lifetime

Make the necessary changes in Program.cs

builder.Services.AddScoped<ISnapShotCheckWithScope, SnapShotCheckWithScope>();
/// UnComment this line and see whether the code executed or not.
/// you will get a runtime error
//builder.Services.AddSingleton<ISnapShotCheckWithSingleton, SnapShotCheckWithSingleton>();

As IOptionsSnapshot interface has been registered as Scoped, it cannot be injected into Singleton Services. Please look at the source code available in GitHub to understand more on this.

Let us go ahead and execute the Scoped controller.

Options Pattern in .NET 6.0

This interface will read updated configuration data after the app has started.

Use IOptionsMonitor<T> Interface

It is used to read configuration data and notify whenever there is a change in configuration data.
It is registered as Singleton and can be injected into any service lifetime.
It does support:
- Change Notification
- Named Option
- Reloadable configuration
- Selective options invalidation – please refer MS documentation for more details

Let us go through the code snippets.

Appsettings.json changes

"MonitorOption": {
    "InterfaceName": "IOptionsMonitor"
}

A few classes added as below

Options Class

public class MonitorOption
{
    public const string Position = "MonitorOption";
    public string InterfaceName { get; set; }  
}

Interface and classes as below

public interface IOptionsMonitorCheck
{
    Task<string> CheckOptionMonitor();
}

public class OptionMonitorCheck : IOptionsMonitorCheck
{
    private readonly MonitorOption _monitorOption;
    public OptionMonitorCheck(IOptionsMonitor<MonitorOption> optionsMonitor) =>
        (_monitorOption) = (optionsMonitor.CurrentValue);
    public Task<string> CheckOptionMonitor()
    {
        var interfaceName = this._monitorOption.InterfaceName;
        return Task.FromResult(interfaceName);
    }
}

Controller as below

public class OptionMonitorController : ControllerBase
{
    private readonly IOptionsMonitorCheck _optionsMonitorCheck;
    public OptionMonitorController(IOptionsMonitorCheck monitorCheck)=>
        (_optionsMonitorCheck) = (monitorCheck);
    [HttpGet]
    [Route("optionsMonitor")]
    public IActionResult OptionsMonitor()
    {
        var interfaceName = this._optionsMonitorCheck.CheckOptionMonitor();
        return Ok(interfaceName);
    }
}

Changes in Program.cs as below

builder.Services.AddScoped<IOptionsMonitorCheck, OptionMonitorCheck>();
//Uncomment each of the below one at a time and see how this behaves
//builder.Services.AddSingleton<IOptionsMonitorCheck, OptionMonitorCheck>();
//builder.Services.AddTransient<IOptionsMonitorCheck, OptionMonitorCheck>();

Let us go ahead and debug the controller OptionMonitorController.cs. Here we are registering the interface – IoptionMonitorCheck as Scope.

Options Pattern in .NET 6.0

Now change from Scoped to Singleton in Program.cs and see how this behaves.

//builder.Services.AddScoped<IOptionsMonitorCheck, OptionMonitorCheck>();
//Uncomment each of the below one at a time and see how this behaves
builder.Services.AddSingleton<IOptionsMonitorCheck, OptionMonitorCheck>();
//builder.Services.AddTransient<IOptionsMonitorCheck, OptionMonitorCheck>();

Options Pattern in .NET 6.0

Successfully execute.

Now let us change to Transient in Program.cs and see.

//builder.Services.AddScoped<IOptionsMonitorCheck, OptionMonitorCheck>();
//Uncomment each of the below one at a time and see how this behaves
//builder.Services.AddSingleton<IOptionsMonitorCheck, OptionMonitorCheck>();
builder.Services.AddTransient<IOptionsMonitorCheck, OptionMonitorCheck>();

Options Pattern in .NET 6.0

Execute successfully.

We have seen how to read configuration data using Options pattern in .NET 6.0. This approach will ensure two engineering principles – encapsulation and separation of concerns. Hope this article helps you to understand the Options pattern at high level. Thank you for reading my article and please leave your comments in the comment box below.