options-without-IOptions.md

Using T options classes instead of IOptions<T>

• Motivation
• Requirements
• How to use

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

Note

the variable services in the examples below is of type IServiceCollection. On the default template for a Web API you can access it via builder.services. Example:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();

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();

Note

The AddOptionsValue extension methods add the ability to take a dependency on SomeOption, they don't remove remove the ability to take a dependency on IOptions<SomeOption>.