options-without-IOptions.md

Using T options classes instead of IOptions<T>

Motivation

I want to be able inject the options type T as a dependency instead of IOptions<T>.

The docs for the options pattern used in asp.net core apps explains how you can read configuration values and use them through your app. However, there might be cases where you do not require the advantages provided by IOptions and want just to use an instance of the typed configuration.

Requirements

You will have to add the dotnet-sdk-extensions nuget to your project.

How to use

Imagine that you have an appsettings file with the following:

"MyOptionsSection": {
    "SomeOption": "hi"
}

Which is represented by the typed class MyOptions:

public class MyOptions
{
    public string SomeOption { get; set; }
}

And now you want to take the MyOptions type as a dependency. As an example:

public class SomeClass
{
    public SomeClass(SomeOption someOption)
    {

    }
}

To be able to do the above you can use the OptionsBuilder.AddOptionsValue extension method:

services
    .AddOptions<MyOptions>()
    .Bind(configuration.GetSection("MyOptionsSection"))
    .AddOptionsValue();

Equivalently to the above, you can use the IServiceCollection.AddOptionsValue extension method:

services.AddOptionsValue<MyOptions>(_configuration, sectionName: "MyOptionsSection");

In the first example you are still required to have called IServiceCollection.AddOptions (and optionally configure your options as desired) before using OptionsBuilder.AddOptionsValue. In the second example, you get a 'shortcut' way of calling it which should work for most scenarios and still allow you to further configure the options class MyOptions by using other OptionsBuilder methods. For instance:

services
    .AddOptionsValue<MyOptions>(_configuration, sectionName: "MyOptionsSection")
    .ValidateDataAnnotations();

Also note that this extension method just added the ability to take a dependency on SomeOption, it didn't remove the ability to take a dependency on IOptions<SomeOption>.