concept ConfigurationBuilder in category asp.net

This is an excerpt from Manning's book ASP.NET Core in Action. Login to get full access to this book.

The ConfigureAppConfiguration() method is the focus of section 11.3. It’s where you load the settings and secrets for your app, whether they’re in JSON files, environment variables, or command-line arguments. In the next section, you’ll see how to use this method to load configuration values from various configuration providers using the ASP.NET Core ConfigurationBuilder.

ConfigurationBuilder describes how to construct the final configuration representation for your app, and IConfigurationRoot holds the configuration values themselves.

You describe your configuration setup by adding a number of IConfigurationProviders to IConfigurationBuilder. These describe how to load the key-value pairs from a particular source; for example, a JSON file or from environment variables, as shown in figure 11.2. Calling Build() on ConfigurationBuilder queries each of these providers for the values they contain to create the IConfigurationRoot instance.

Figure 11.2. Using ConfigurationBuilder to create an instance of IConfigurationRoot. Configuration providers are added to the builder with extension methods. Calling Build() queries each provider to create IConfigurationRoot.

Listing 11.5. Loading appsettings.json using a custom WebHostBuilder

public class Program { public static void Main(string[] args) { BuildWebHost(args).Run(); } public static IWebHost BuildWebHost(string[] args) => new WebHostBuilder() .UseKestrel() .UseContentRoot(Directory.GetCurrentDirectory()) .ConfigureAppConfiguration(AddAppConfiguration) #1 .ConfigureLogging( (hostingContext, logging) => { /* Detail not shown */ }) .UseIISIntegration() .UseDefaultServiceProvider( (context, options) =>{ /* Detail not shown */ }) .UseStartup<Startup>() .Build(); public static void AddAppConfiguration( #2 WebHostBuilderContext hostingContext, #2 IConfigurationBuilder config) #2 { config.AddJsonFile("appsettings.json", optional: true); #3 } } #1 Adds the configuration setup function to WebHostBuilder #2 WebHostBuilder provides a hosting context and an instance of ConfigurationBuilder. #3 Adds a JSON configuration provider, providing the filename of the configuration file

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ConfigurationBuilder describes how to construct the final configuration representation for your app and IConfigurationRoot holds the configuration values themselves.

You create a configuration object by adding configuration providers to an instance of ConfigurationBuilder using extension methods such as AddJsonFile(). WebHostBuilder creates the ConfigurationBuilder instance for you and calls Build() to create an instance of IConfigurationRoot.