Options Pattern In .NET 6.0

  "Units": {
    "Temp": "Celsius",
    "Distance": "Miles"
  }

public class UnitOptions
{
	public string Temp { get; set; } = String.Empty;
	public string Distance { get; set; } = String.Empty;
}

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

public interface ITransientService
{
	UnitOptions GetUnits();
}

public class TransientService : ITransientService
{
    private readonly UnitOptions _unitOptions;

    public TransientService(IOptions<UnitOptions> unitOptions)
    {
        _unitOptions = unitOptions.Value;
    }
    public UnitOptions GetUnits()
    {
        return _unitOptions;
    }
}

builder.Services.AddTransient<ITransientService, TransientService>();

[Route("api/[controller]")]
[ApiController]
public class OptionsDemoController : ControllerBase
{
    private readonly ITransientService _transientService;

    public OptionsDemoController(TransientService transientService)
    {
        _transientService = transientService;
    }

    [HttpGet]
    [Route("/units/transient")]
    public IActionResult GetUnitsTransient() => Ok(_transientService.GetUnits());
}

public interface IScopedService
{
	UnitOptions GetUnits();
}

public class ScopedService : IScopedService
{
    private readonly UnitOptions _unitOptions;

    public ScopedService(IOptionsSnapshot<UnitOptions> unitOptions)
    {
        _unitOptions = unitOptions.Value;
    }

    public UnitOptions GetUnits()
    {
        return _unitOptions;
    }
}

Add the scoped service to DI container in Program.cs

builder.Services.AddScoped<IScopedService, ScopedService>();

Hook the service to the controller

[Route("api/[controller]")]
[ApiController]
public class OptionsDemoController : ControllerBase
{
    private readonly IScopedService _scopedService;
    private readonly ITransientService _transientService;

    public OptionsDemoController(ITransientService transientService, IScopedService scopedService)
    {
        _transientService = transientService;
        _scopedService = scopedService;
    }

    [HttpGet]
    [Route("/units/scoped")]
    public IActionResult GetUnitsScoped() => Ok(_scopedService.GetUnits());

    [HttpGet]
    [Route("/units/transient")]
    public IActionResult GetUnitsTransient() => Ok(_transientService.GetUnits());
}

Run the app and hit the controller action. You should be able to see the values being fetched from the configuration file.

While the app is still running, change the value of distance unit from ‘Miles’ to ‘Kilometres’ in the appsettings.json file and hit the same API controller action again. The response reflects the changes to the config data.

If you try to add IOptionsSnapshot to any singleton service, you would encounter a runtime exception because of the service lifetime mismatch.

Revert changes to the appsettings.json file before proceeding with next steps.

IOptionsMonitor

IOptionsMonitor is singleton and hence can be used to read configuration data in any service lifetime. However, as opposed to IOptions, it can retrieve current config data at any time.

Create a singleton service with an injected IOptionsMonitor instance as follows:-

public interface ISingletonService
{
    UnitOptions GetUnits();
}

public class SingletonService : ISingletonService
{
    private readonly IOptionsMonitor<UnitOptions> _unitOptions;

    public SingletonService(IOptionsMonitor<UnitOptions> unitOptions)
    {
        _unitOptions = unitOptions;
    }
    public UnitOptions GetUnits()
    {
        return _unitOptions.CurrentValue;
    }
}

Add the service to DI container in Program.cs

builder.Services.AddSingleton<ISingletonService, SingletonService>();

Hook the service to controller

[Route("api/[controller]")]
[ApiController]
public class OptionsDemoController : ControllerBase
{
    private readonly ITransientService _transientService;
    private readonly IScopedService _scopedService;
    private readonly ISingletonService _singletonService;

    public OptionsDemoController(ITransientService transientService, IScopedService scopedService, ISingletonService singletonService)
    {
        _transientService = transientService;
        _scopedService = scopedService;
        _singletonService = singletonService;
    }

    [HttpGet]
    [Route("/units/transient")]
    public IActionResult GetUnitsTransient() => Ok(_transientService.GetUnits());


    [HttpGet]
    [Route("/units/scoped")]
    public IActionResult GetUnitsScoped() => Ok(_scopedService.GetUnits());

    [HttpGet]
    [Route("/units/singleton")]
    public IActionResult GetUnitsSingleton() => Ok(_singletonService.GetUnits());
}

Run the app and hit the controller action. You should be able to see the values being fetched from the configuration file.

While the app is still running, change the value of distance unit from ‘Miles’ to ‘Kilometres’ in the appsettings.json file and hit the same API controller action again. The response reflects the changes to the config data.

Summary

The options pattern provides us with various options to read the config data using strongly types classes. Depending upon service lifetime and recomputation requirements of the config data, one can use IOptions, IOptionsSnapshot, and IOptionsMonitor interfaces to read config data. Prefer using the options pattern over other methods to read config data.

References

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/configuration/options?view=aspnetcore-6.0