IConfiguration type binding for properties in Options pattern.

[armandjnbg]

Hello everybody,

I defined the following configuration option class for use with Options pattern:

public class RouteOptions
{
   public string Name { get; set; }
   public string Local { get; set; }
   public string Remote { get; set; }
   public string HttpClientName { get; set; }
   . . .
   public IConfiguration Extra { get; set; }
}

The "Extra" field by my design would include various extra settings that will be accessed by business logic located outside of my code, e.g. plugins written by other developers. I was expecting this to work, but to my surprise, this property is never assigned.

Probably it is very easy to bind this field it does not require any conversion, just assign GetSection("propertyName") to the property.

Is it possible to introduce this functionality?

I think it is essential.

With best regards,
Arman

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

Tagging subscribers to this area: @maryamariyan
See info in area-owners.md if you want to be subscribed.

[pinkfloydx33]

You can register an I[Post]ConfigureOptions implementation that assigns to your property:

public class ConfigureRouteOptions : IConfigureOptions<RouteOptions>, IPostConfigureOptions<RouteOptions>
{
   private readonly IConfiguration _config;
   public ConfigureRouteOptions(IConfiguration config)
      => _config = config.GetSection("Whatever"); // 4

   public void Configure(RouteOptions opts) // 1
   {
         _config.Bind(opts); // 3
         opts.Extra = _config.GetSection("Extra"); 
   }

  public void PostConfigure(string name, RouteOptions opts) // 2
  {
        if(opts.Extra is null) 
           opts.Extra = _config.GetSection("Extra");
  } 
}

You can either user IConfigureOptions (1) or IPostConfigureOptions (2)--or technically both. You register this with the service collections as:

services.ConfigureOptions<ConfigureRouteOptions>();

If you've already bound your configuration (via a call to Configure<RouteOptions>) then binding the "main" properties manually (3) wouldn't be necessary. In fact you'd probably need to guard properly against that case to be sure you don't discard any prior configuration. All IConfigureOptions run first, followed by all IPostConfigureOptions--so just something to keep in mind. I'd probably select the Post-Configure version myself.

The only downside here is that your root section name (4) is hard-coded. That may not be a problem, but if it is you can provide the configurator with its own options class. Something like:

public class ConfiguratorOpts
{
   public string RootSection { get; set; } = "DefaultValue";
}

public class ConfigureRouteOptions : IConfigureOptions<RouteOptions>, IPostConfigureOptions<RouteOptions>
{
   private readonly IConfiguration _config;
   public ConfigureRouteOptions(IConfiguration config, IOptions<ConfiguratorOpts> opts /* 5 */)
      => _config = config.GetSection(opts.Value.RootSection); // 4

   public void Configure(RouteOptions opts) // 1
   {
         _config.Bind(opts); // 3
         opts.Extra = _config.GetSection("Extra"); 
   }

  public void PostConfigure(string name, RouteOptions opts) // 2
  {
        if(opts.Extra is null) 
           opts.Extra = _config.GetSection("Extra");
  } 
}

The section name can then be read from your configuration (5)--or the default value. You'd register it using:

services.Configure<ConfiguratorOpts>(o => o.RootSection = "SomethingElse");
services.ConfigureOptions<ConfigureRouteOptions>();

While it's not built-in and automatic, it's definitely a way to achieve what you are looking to accomplish.

[armandjnbg]

Thanks,

Your solution is applicable in my case, but my case is a bit more complex because RouteOptions include inner RouteOptions.
Plus RootOptions themself reside inside of another configuration element RouteMap. So it a tree-like structure in the config. So I don't have a section name for reading each of that RouteOption representation in the configuration.

    public class RouteOptions
{
	public string Name { get; set; }
	public string Local { get; set; }
	public string Remote { get; set; }
	public string HttpClientName { get; set; }

	public bool Validate { get; set; } = true;
	public bool Audit { get; set; } = true;

	public ClaimValidationOptions[] Claims { get; set; }

	IConfigurationSection Extra { get; set; }

            // inner elements here
	public List<RouteOptions> Inner { get; set; }
}

I will write a custom code for reading this tree from the configuration, based on recursive call to IPostConfigureOptions probably.

But I was thinking that it would be good to include out of the box IConfigurationSection binding somewhere in the next versions of .NET Core, this doesn't seem like require significant changes to the existing code of configuration binder.

So I guess this is a feature request. :-)

With best regards,
Arman

[KalleOlaviNiemitalo]

it would be good to include out of the box IConfigurationSection binding somewhere in the next versions of .NET Core

IConfigurationSection binding works in .NET 6.0 already, although IConfiguration binding doesn't:

using System;
using System.Collections.Generic;
using Microsoft.Extensions.Configuration;

IConfiguration configuration = new ConfigurationBuilder()
    .AddInMemoryCollection(
        new KeyValuePair<string, string>[]
        {
            new KeyValuePair<string, string>("Name", "Kaur"),
            new KeyValuePair<string, string>("Extra:hello", "world"),
        })
     .Build();
var routeOptions = configuration.Get<RouteOptions>();

Console.WriteLine(routeOptions.Name);
Console.WriteLine(routeOptions.Extra["hello"]);

public class RouteOptions
{
   public string Name { get; set; }
   public string Local { get; set; }
   public string Remote { get; set; }
   public string HttpClientName { get; set; }
   public IConfigurationSection Extra { get; set; }
}

Output:

Kaur
world

Implemented here:

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/src/ConfigurationBinder.cs

Lines 344 to 348 in 4822e3c

	// if binding IConfigurationSection, break early
	if (type == typeof(IConfigurationSection))
	{
	return config;
	}

It originally came from aspnet/Configuration@3480095.

[rosebyte]

Triage: we can investigate why IConfiguration isn't supported now and consider support it.