Add back Get<T>() extension method to bind objects to configuration values or entire sections

[tugberkugurlu]

I am not sure where I am doing something wrong but I am seeing a weird behaviour in terms of getting parsing the JSON config file.

I would appreciate if someone can have a look and tell me where I am doing something stupid 😞

Repro Steps

git clone git@github.com:tugberkugurlu/AspNetCoreSamples.git
cd AspNetCoreSamples/repros/ConfigSectionNull
git checkout -qf 4101a06ab9ab05ac15ed2824a44ff97c323d371e
dotnet restore
dotnet run

Expected Result

Console output to be equal to below:

'MySecondNode' value is null? False
'RabbitMQ' value is null? False

Actual Result

Console output is equal to below:

'settings' is null
'MySecondNode' value is null? True
'RabbitMQ' value is null? True

dotnet CLI Info

Tugberks-MacBook-Pro:ConfigSectionNull tugberk$ dotnet --info
.NET Command Line Tools (1.0.0-preview2-003121)

Product Information:
 Version:            1.0.0-preview2-003121
 Commit SHA-1 hash:  1e9d529bc5

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.12
 OS Platform: Darwin
 RID:         osx.10.12-x64

Source

Program.cs:

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.PlatformAbstractions;

namespace rabbitsample
{
    public static class Program 
    {   
        public static void Main(string[] args)
        {
            var config = ConfigBuilder.Build();

            var settings = config.GetValue<RabbitMQSettings>("RabbitMQ");
            if(settings == null) 
            {
                System.Console.WriteLine("'settings' is null");
            }

            var cildrenNodes = config.GetChildren();
            foreach (var item in cildrenNodes)
            {
                System.Console.WriteLine($"'{item.Key}' value is null? {item.Value == null}");
            }
        }
    }

    public class RabbitMQSettings 
    {
        public string Host { get; set; }
    }

    public static class ConfigBuilder
    {   
        public static IConfiguration Build()
        {
            return new ConfigurationBuilder()
                .SetBasePath(PlatformServices.Default.Application.ApplicationBasePath)
                .AddJsonFile("config.json")
                .AddEnvironmentVariables("rabbitsample_")
                .Build();
        }
    }
}

project.json:

{
    "version": "1.0.0-*",
    "buildOptions": {
        "debugType": "portable",
        "emitEntryPoint": true,
        "copyToOutput": ["config.json"]
    },
    "dependencies": {
        "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.0.0",
        "Microsoft.Extensions.Configuration.Json": "1.0.0",
        "Microsoft.Extensions.Configuration.Binder": "1.0.0",
        "Microsoft.Extensions.PlatformAbstractions": "1.0.0",
        "Microsoft.Extensions.Options": "1.0.0",
        "Lorem.DNX.NET": "1.0.40",
        "easynetq": "2.0.2-netcore0001"
    },
    "frameworks": {
        "netcoreapp1.0": {
            "dependencies": {
                "Microsoft.NETCore.App": {
                    "type": "platform",
                    "version": "1.0.0"
                }
            },
            "imports": "dnxcore50"
        }
    }
}

config.json:

{
    "RabbitMQ": {
        "Host": "localhost"
    },

    "MySecondNode": {
        "Value1": "1",
        "Value2": "2"
    }
}

[tugberkugurlu]

This made it work: tugberkugurlu/AspNetCoreSamples@87cfde9

That's weird though. Is GetValue<T> only supposed to work for simple types?

[Rick-Anderson]

Here's the sample I've added to the config doc PR

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

// Add NuGet  <package id="Microsoft.Extensions.Configuration.Binder"
public class Program
{   
    static public IConfigurationRoot Configuration { get; set; }
    public static void Main(string[] args = null)
    {
        var dict = new Dictionary<string, string>
            {
                {"Profile:MachineName", "Rick"},
                {"App:MainWindow:Height", "11"},
                {"App:MainWindow:Width", "11"},
                {"App:MainWindow:Top", "11"},
                {"App:MainWindow:Left", "11"}
            };

        var builder = new ConfigurationBuilder();
        builder.AddInMemoryCollection(dict);
        Configuration = builder.Build();
        Console.WriteLine($"Hello {Configuration["Profile:MachineName"]}");

        // Show GetValue overload and set the default value to 80
        // You typically would set default values in the constructor.
        // Requires NuGet package "Microsoft.Extensions.Configuration.Binder"
        var left = Configuration.GetValue<int>("App:MainWindow:Left", 80);
        Console.WriteLine($"Left {left}");

        var window = new MyWindow();
        Configuration.GetSection("App:MainWindow").Bind(window);
        Console.WriteLine($"Left {window.Left}");
    }
}

[tugberkugurlu]

thanks @Rick-Anderson!

After getting help from Twitter people and digging into the source code, I discovered that GetValue<T> API is not what I wanted. I think it only works for certain types if I am not mistaken (e.g. simple types like int, string, etc.) and it will never work for something like MySettings, correct?

It could have been better if it gave feedback about those situations rather than just returning null directly (e.g. throw saying that it cannot convert that type, etc.). However, I would more prefer for it to use ConfigurationBinder.Bind under the hood and do the right thing.

[HaoK]

Yep it's basically a convert. It's been a common source of confusion so far.

On Oct 21, 2016, at 1:41 PM, Tugberk Ugurlu notifications@github.com wrote:

This made it work: tugberkugurlu/AspNetCoreSamples@87cfde9

That's weird though. Is GetValue only supposed to work for simple types?

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[HaoK]

After discussion with @divega @glennc we've decided to bring back Get<T>() which will 'do the right thing' for the majority of cases where T is convertible/bindable from either the Value/Children.

We'll need to hash out some of the specific details for some of the edge cases and the heuristics, but that discussion can go in the PR.

[HaoK]

Also this will eliminate the need for the T Bind<T>() that we added in 1.1-preview1, I'll remove that method as part of this change

[tugberkugurlu]

@HaoK 🎉 🎉 thanks a lot!

[HaoK]

Associated PR for this work: #535

[HaoK]

d73b261