Configuration in ASP.NET Core

In ASP.NET Core application configuration settings like the database connection strings or some key value can come from the following different configurations sources.

• Files (appsettings.json, appsettings.{Environment}.json, where {Environment} is the app's current hosting environment)
• User secrets
• Environment variables
• Command-line arguments

ASP.NET Core IConfiguration service

• IConfiguration service is setup to read configuration information from all the various configuration sources in asp.net core
• If you have a configuration setting with the same key in multiple configuration sources, the later configuration sources override the earlier configuration sources 
• CreateDefaultBuilder() method of the WebHost class which is automatically invoked when the application starts, reads the configuration sources in a specific order.
• Following is the default order in which the various configuration sources are read

1. appsettings.json
2. appsettings.{Environment}.json
3. User secrets
4. Environment variables
5. Command-line arguments

This order can be changed or one can even add own custom configuration sources in addition to all the existing configuration sources. 

 

EXAMPLE

appsettings.json file: In this file we can add itme as key value pair 

{  

  "AllowedHosts": "*",

  "MyKeyValue": "Value of MyKey from appsettings.json"

}

Accessing configuration information 

To access configuration information in the Startup class, inject the IConfiguration service provided by the Framework.

public class Startup

{

    private IConfiguration _configuration;

    // Notice we are using Dependency Injection here

    public Startup(IConfiguration configuration)

    {

        _configuration = configuration;

    }

    public void ConfigureServices(IServiceCollection services)

    {

    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)

    {

        if (env.IsDevelopment())

        {

            app.UseDeveloperExceptionPage();

        }

        app.Run(async (context) =>

        {

            await context.Response.WriteAsync(_configuration["MyKeyValue"]);

        });

    }

}