MSDN Documentation

ASP.NET Core Configuration

ASP.NET Core uses a flexible configuration system that allows you to manage application settings from various sources. This system is designed to be environment-agnostic and easily extensible. Configuration values are read as key-value pairs, typically represented as strings.

Configuration Providers

The configuration system in ASP.NET Core is built around configuration providers. Each provider reads configuration data from a specific source. The framework includes several built-in providers:

• JSON files: appsettings.json and appsettings.{Environment}.json are common sources.
• Environment Variables: Settings can be read from environment variables.
• Command-line arguments: Configuration can be passed via the command line.
• User Secrets: For development environments, sensitive settings can be stored locally.
• Azure Key Vault: Secure storage for production environments.

The order in which providers are added to the configuration builder is important, as it determines the precedence of settings. Later providers can override settings from earlier ones.

IConfiguration Interface

The primary way to access configuration data in your ASP.NET Core application is through the IConfiguration interface. This interface provides methods to retrieve configuration values by key.

Example: Reading a setting

using Microsoft.Extensions.Configuration;
using System;

// Assuming 'configuration' is an instance of IConfiguration, typically injected
var settingValue = configuration["MySetting:SubSetting"];

if (settingValue != null)
{
    Console.WriteLine($"MySetting:SubSetting = {settingValue}");
}
else
{
    Console.WriteLine("MySetting:SubSetting not found.");
}

Configuration Binding

While reading individual settings is useful, it's often more convenient to bind configuration values to strongly-typed objects. This makes your code cleaner and more maintainable.

Example: Binding to a class

First, define a class that mirrors your configuration structure:

public class AppSettings
{
    public string ApiKey { get; set; }
    public int TimeoutSeconds { get; set; }
}

Then, bind it in your application's setup (e.g., in Program.cs or Startup.cs):

// Assuming 'configuration' is an instance of IConfiguration
            var appSettings = new AppSettings();
            configuration.GetSection("AppSettings").Bind(appSettings);

            // You can now use appSettings.ApiKey and appSettings.TimeoutSeconds
            

Environments and Configuration

ASP.NET Core makes it easy to manage configuration for different environments (e.g., Development, Staging, Production). The ASPNETCORE_ENVIRONMENT environment variable is used to specify the current environment. The configuration system automatically loads settings from files named appsettings.{Environment}.json.

Example Structure:

• appsettings.json (default settings)
• appsettings.Development.json (settings for development)
• appsettings.Production.json (settings for production)

Custom Configuration Providers

You can create custom configuration providers to read settings from any source, such as databases, custom file formats, or external services. This allows for maximum flexibility in managing your application's configuration.

Summary

The ASP.NET Core configuration system is a powerful and flexible tool. By understanding configuration providers, the IConfiguration interface, and configuration binding, you can effectively manage your application's settings across different environments and deployment scenarios.