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dotnet-primer

Configuration

What this covers

Section titled “What this covers”

Configuration comes from layered providers: appsettings.json, then appsettings.{Environment}.json, then user secrets, environment variables and the command line, with later layers winning. This page covers reading values through IConfiguration, binding sections to typed classes with the options pattern, and validating options at startup.

A taste of the options pattern:

Program.cs
using Microsoft.Extensions.Options;


var builder = WebApplication.CreateBuilder(args);


builder.Services.Configure<GreetingOptions>(
    builder.Configuration.GetSection(GreetingOptions.SectionName));


var app = builder.Build();


app.MapGet("/greeting", (IOptions<GreetingOptions> options) => options.Value.Message);


app.Run();


public sealed class GreetingOptions
{
    public const string SectionName = "Greeting";
    public string Message { get; set; } = "";
}

Exercise 01: bind configuration to options

Section titled “Exercise 01: bind configuration to options”

Goal: serve a greeting whose text comes from configuration, so it can be changed per environment without touching code.

Where: samples/exercises/01-configuration in the GitHub repo. Clone the repo, then work in the Starter project.

Steps:

  1. Open Starter/Program.cs and find the TODO comments.
  2. Bind the Greeting section of configuration to GreetingOptions.
  3. Make GET /greeting return GreetingOptions.Message instead of 501 Not Implemented.
  4. Check that an environment variable (Greeting__Message) overrides the value in appsettings.json.

Check your work: the tests start red and turn green as you go.

Terminal window
dotnet test --project samples/exercises/01-configuration/Starter.Tests

Stuck? Compare with the Solution project next to it. The exercises are for practice only, and nothing is recorded or submitted.