C# ASP.NET Core : support both appsettings.json and app.config

Question

I have a shared the library that needs some input from the config file, let's say a database helper class with IConfiguration injected in the constructor.

I have an ASP.NET Core app that uses appsettings.json with database connection string. And there is also a .NET Core console app that uses app.config to provide a database connection string. Both of them use the helper class.

However IConfigration only supports appsettings.json format eg. configuration.GetConnectionString. Is there a way to be able to read from both app.config and appsettings.json in uniform code?

Answer 1

"configuration.GetConnectionString" actually support app.config. But it depends on how you write the config file.
package
Microsoft.Extensions.Configuration
Microsoft.Extensions.Configuration.XML
app.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <ConnectionStrings>
        <DefaultConnection>Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;</DefaultConnection>
    </ConnectionStrings>
</configuration>

    public class DbHelper
    {
        private readonly IConfiguration configuration;

        public DbHelper(IConfiguration configuration)
        {
            this.configuration = configuration;
        }
        public string GetConString()
        {
            return configuration.GetConnectionString("DefaultConnection");
        }
    }

Console App (app.config in debug folder)

var builder = new ConfigurationBuilder()
    .AddXmlFile("app.config", optional: true, reloadOnChange: true);
IConfiguration configuration = builder.Build();
var helper = new DbHelper(configuration);
var conString = helper.GetConString();

Test result