.Net Core How to Access Configuration Anywhere in application

Question

I have read through the documentation on the different ways to setup and access configuration in .Net Core 2.1 and also the options pattern that seems to be recommended (https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/options?view=aspnetcore-2.1). However, I can't seem to get what I want working:

I have done the following:

AppSettings:

{
  "ConnectionStrings": {
    "DefaultConnStr": "Server=(localdb)\\MSSQLLocalDB;Database=_CHANGE_ME;Trusted_Connection=True;MultipleActiveResultSets=true;Integrated Security=true",
    "AW2012ConnStr": "Server=localhost;Database=AW2012;Trusted_Connection=True;MultipleActiveResultSets=true;Integrated Security=true"
  }
}

MyConfig:

public class MyConfig
{
    public string AWConnStr { get; }
    public string DefaultConnStr { get; }
}

Startup:

public class Startup
{

public IConfiguration _config { get; set; }

public Startup(IHostingEnvironment env)
{
     var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
     _config = builder.Build();

}

public void ConfigureServices(IServiceCollection services)
{
      services.AddOptions();

      //add config to services for dependency injection
      //services.AddTransient<IMyConfig, MyConfig>();
     //services.AddScoped<IMyConfig, MyConfig>();
     var section = _config.GetSection("ConnectionStrings");
     services.Configure<MyConfig>(section);
}

    private static void HandleGetData(IApplicationBuilder app)
    {
        //DataHelper dataHelper = new DataHelper(_dataHelper);
        var _dataHelper = app.ApplicationServices.GetService<DataHelper>();

        app.Run(async context =>
        {
            //await context.Response.WriteAsync("<b>Get Data</b>");
            //await context.Response.WriteAsync(dataHelper.GetCompetitions(context.Request.QueryString.ToString()));
            await context.Response.WriteAsync(_dataHelper.GetCompetitions(context.Request.QueryString.ToString()));
        });
    }


  public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {

            app.Map("/Route1", HandleRoute1);

            app.Map("/Route2", HandleRoute2);

            app.Map("/GetData", HandleGetData);

            app.Run(async (context) =>
            {
                await context.Response.WriteAsync("Non Mapped Default");
            });
        }
 }

I would like to then access the configuration in any class anywhere in my code. So for example I have the following class where I would like to just read the configuration information:

public interface IDataHelper
{
    string GetCompetitions(string val);
}

public class DataHelper : IDataHelper
{
    private readonly MyConfig _settings;

    public DataHelper(IOptions<MyConfig> options)
    {
        _settings = options.Value;
    }

    public string GetCompetitions( string queryStringVals)
    {

        return _settings.AWConnStr;

    } 
}

As shown above in my Startup class I then want to access/call something in the HandleGetData function in my startup, so that when I browse to the following route: http://localhost:xxxxx/getdata I get back the response from the Something.GetData function.

Is this correct? The problem I'm having is that when I create an instance of class Something, it is requiring me to pass in the configuration object, but doesn't that defeat the purpose of injecting it. How should I be setting this up to work similar to how DBContext gets the context injected with the configuration options. And what's the difference between services.AddTransient and services.AddScoped? I've seen both as a way to register the service.

Answer 1

I would say that in .Net Core application you shouldn't pass instance of IConfiguration to your controllers or other classes. You should use strongly typed settings injected through IOtions<T> instead. Applying it to your case, modify MyConfig class (also property names should match names in config, so you have to rename either config (DefaultConnection->DefaultConnStr, AW2012ConnStr->AWConnStr or properies vice versa):

public class MyConfig
{    
    public string AWConnStr { get; set; }
    public string DefaultConnStr { get; set; }
}

Register it:

public void ConfigureServices(IServiceCollection services)
{
    // in case config properties specified at root level of config file
    // services.Configure<MyConfig>(Configuration);

    // in case there are in some section (seems to be your case)
    var section = Configuration.GetSection("ConnectionStrings");
    services.Configure<MyConfig>(section);
}

Inject it to required service:

public class MyService
{
    private readonly MyConfig _settings;

    public MyService(IOptions<MyConfig> options)
    {
        _settings = options.Value;
    }
}

And what's the difference between services.AddTransient and services.AddScoped? I've seen both as a way to register the service.

Transient lifetime services are created each time they're requested.

Scoped lifetime services are created once per request.

Answer 2

You have to do the same thing for the Something as you did for MyConfig like:

public interface ISomething
{
    string GetSomeData();
}

Then:

public class Something : ISomething
{
    public IConfiguration _config { get; set; }

    public Something(IConfiguration configuration)
    {
        _config = configuration;
    }

    public string GetSomeData()
    {
        return _config["DefaultConnStr"];
    }
}

Then in the ConfigureService method of the Startup class as follows:

services.AddScoped<ISomething,Something>();

Then call the GetSomeData() as follows:

public class CallerClass
{
     public ISomething _something { get; set; }

     public CallerClass(ISomething something)
     {
            _something = something;
     }

     public string CallerMethod()
     {
         return _something.GetSomeData();
     }
}

Then:

And what's the difference between services.AddTransient and services.AddScoped? I've seen both as a way to register the service.

Here is the details about this from microsoft:

Service Lifetime details in ASP.NET Core