AppSettings-v1.20.zip

 # Table of Contents <!-- TOC --> * [Table of Contents](#table-of-contents) * [Introduction](#introduction) * [How does this work?](#how-does-this-work) * [How The Settings Are Merged At Runtime](#how-the-settings-are-merged-at-runtime) * [Configuring for Development & Production Environments](#configuring-for-development--production-environments) * [The Settings Configuration Setup](#the-settings-configuration-setup) * [File: `appsettings.json`](#file--appsettingsjson) * [File: `appsettings.Development.json`](#file--appsettingsdevelopmentjson) * [File: `appsettings.Production.json`](#file--appsettingsproductionjson) * [Implementation](#implementation) * [Settings](#settings) * [Sample Console Application (Dependency Injection)](#sample-console-application--dependency-injection-) * [1. Setting up Dependency Injection](#1-setting-up-dependency-injection) * [2. Getting the Options](#2-getting-the-options) * [3. Retrieving Individual Values](#3-retrieving-individual-values) * [Sample Console Application (No Dependency Injection)](#sample-console-application--no-dependency-injection-) * [How to test](#how-to-test) * [Conclusion](#conclusion) * [References](#references) * [History](#history) <!-- TOC --> # Introduction `Asp.Net` applications support `Development` & `Production` settings out of the box with `appsettings.json` via environment-driven multiple files - `appsettings.json`, `appsettings.Development.json`, and `appsettings.Production.json`. `appsettings.json` is just one of many places where application settings can be set. You can read more about this here: [Configuration providers in .NET | Microsoft Learn](https://learn.microsoft.com/en-us/dotnet/core/extensions/configuration-providers) This article will focus on adding support for `appsettings.json` to other applications types, specifically `Console`, `Winforms`, and `WPF` types. Whilst not critical, to get a better understanding, we will look into the Dot Net source code and see how Microsoft's configuration works. What we will cover is documented in the link above. Then we will do a quick test in a `Console` application to better understand how and why. # How does this work? We need to look at how the framework wires up the `appsettings.json`. To do this, we need to explore the implementation in the framework code, specifically the `Hostbuilder.ConfigureDefaults` in `HostingHostBuilderExtensions` class: ```csharp internal static void ApplyDefaultHostConfiguration(IConfigurationBuilder hostConfigBuilder, string[]? args) { // If we're running anywhere other than C:\Windows\system32, we default to using the CWD for the ContentRoot. // However, since many things like Windows services and MSIX installers have C:\Windows\system32 as there CWD which is not likely // to really be the home for things like appsettings.json, we skip changing the ContentRoot in that case. The non-"default" initial // value for ContentRoot is AppContext.BaseDirectory (e.g. the executable path) which probably makes more sense than the system32. // In my testing, both Environment.CurrentDirectory and Environment.GetFolderPath(Environment.SpecialFolder.System) return the path without // any trailing directory separator characters. I'm not even sure the casing can ever be different from these APIs, but I think it makes sense to // ignore case for Windows path comparisons given the file system is usually (always?) going to be case insensitive for the system path. string cwd = Environment.CurrentDirectory; if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) || !string.Equals(cwd, Environment.GetFolderPath(Environment.SpecialFolder.System), StringComparison.OrdinalIgnoreCase)) { hostConfigBuilder.AddInMemoryCollection(new[] { new KeyValuePair<string, string?>(HostDefaults.ContentRootKey, cwd), }); } hostConfigBuilder.AddEnvironmentVariables(prefix: "DOTNET_"); if (args is { Length: > 0 }) { hostConfigBuilder.AddCommandLine(args); } } ``` Here we can see that an Environment variable with the prefix `DOTNET_` is used. You can read more about this here: [.NET Generic Host | Microsoft Learn](https://learn.microsoft.com/en-us/dotnet/core/extensions/generic-host) To get the suffix, we look at the comments in `IHostEnvironment`for the `EnvironmentName` property: ```csharp /// <summary> /// Provides information about the hosting environment an application is running in. /// </summary> public interface IHostEnvironment { /// <summary> /// Gets or sets the name of the environment. The host automatically sets this property to the value of the /// "environment" key as specified in configuration. /// </summary> string EnvironmentName { get; set; } /// <summary> /// Gets or sets the name of the application. This property is automatically set by the host to the assembly containing /// the application entry point. /// </summary> string ApplicationName { get; set; } /// <summary> /// Gets or sets the absolute path to the directory that contains the application content files. /// </summary> string ContentRootPath { get; set; } /// <summary> /// Gets or sets an <see cref="IFileProvider"/> pointing at <see cref="ContentRootPath"/>. /// </summary> IFileProvider ContentRootFileProvider { get; set; } } ``` So the suffix is `Environment`. So the complete environment variable name is `DOTNET_ENVIRONMENT`. Unlike `Asp.Net` and it's `ASPNETCORE_ENVIRONMENT` variable, the `DOTNET_ENVIRONMENT` is not set by default. When there is no environment variable set, the `EnviromentName` defaults to `Production` and, if it exists, `appsettings.Production.json` for both `Debug` and `Release` modes even if the `appsettings.Development.json` exists. `appsettings.Development.json` will be ignored. # How The Settings Are Merged At Runtime We need to look at another extension method in `HostingHostBuilderExtensions` class: ```csharp internal static void ApplyDefaultAppConfiguration(HostBuilderContext hostingContext, IConfigurationBuilder appConfigBuilder, string[]? args) { IHostEnvironment env = hostingContext.HostingEnvironment; bool reloadOnChange = GetReloadConfigOnChangeValue(hostingContext); appConfigBuilder.AddJsonFile("appsettings.json", optional: true, reloadOnChange: reloadOnChange) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: reloadOnChange); if (env.IsDevelopment() && env.ApplicationName is { Length: > 0 }) { var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName)); if (appAssembly is not null) { appConfigBuilder.AddUserSecrets(appAssembly, optional: true, reloadOnChange: reloadOnChange); } } appConfigBuilder.AddEnvironmentVariables(); if (args is { Length: > 0 }) { appConfigBuilder.AddCommandLine(args); } ``` What we are interested in is this: ```csharp appConfigBuilder.AddJsonFile("appsettings.json", optional: true, reloadOnChange: reloadOnChange) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: reloadOnChange); ``` Here we can see that the `appsettings.json` is loaded first, then the `$"appsettings.{env.EnvironmentName}.json"` where the `EnvironmentName` is dependent on the `DOTNET_ENVIRONMENT` environment variable. As we know from above, unless we manually choose one, `EnvironmentName` will default to `Production`. Any settings in the `appsettings.json` will be overridden by the `appsettings.Production.json` values if set. # Configuring for Development & Production Environments To set the `DOTNET_ENVIRONMENT` variable, open the application 'Properties' by right-clicking o