Microsoft.Extensions.Configuration: Cannot get strongly-typed object from JSON file

[vaindil]

Describe the bug

I am unable to use any strongly-typed methods to convert a JSON file to a configuration object. I don't know if I'm doing something wrong, but it seems pretty straightforward and I'm not sure how I could be messing it up.

To Reproduce

Run this attached code.

Expected behavior

The variable val should not be null near the end of the program, and the last line should return false instead of true. Instead, the last line is true and the config object is not instantiated.

Screenshots

N/A

Additional context

Tested on Windows 10:

.NET Core SDK (reflecting any global.json):
 Version:   2.2.100-preview2-009404
 Commit:    f4707d384d

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17763
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.2.100-preview2-009404\

Host (useful for support):
  Version: 2.2.0-preview2-26905-02
  Commit:  ad4d306fe0

.NET Core SDKs installed:
  2.1.202 [C:\Program Files\dotnet\sdk]
  2.1.403 [C:\Program Files\dotnet\sdk]
  2.1.500-preview-009297 [C:\Program Files\dotnet\sdk]
  2.1.500-preview-009335 [C:\Program Files\dotnet\sdk]
  2.1.500-preview-009404 [C:\Program Files\dotnet\sdk]
  2.1.500 [C:\Program Files\dotnet\sdk]
  2.2.100-preview2-009404 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.0-preview2-35157 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.0-preview2-35157 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.0-preview2-26905-02 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

Tested on Bash on Windows 10:

.NET Core SDK (reflecting any global.json):
 Version:   2.1.500
 Commit:    b68b931422

Runtime Environment:
 OS Name:     ubuntu
 OS Version:  18.04
 OS Platform: Linux
 RID:         ubuntu.18.04-x64
 Base Path:   /usr/share/dotnet/sdk/2.1.500/

Host (useful for support):
  Version: 2.1.6
  Commit:  3f4f8eebd8

.NET Core SDKs installed:
  2.1.500 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.6 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.6 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.6 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

[vaindil]

In case it's helpful, here's the contents of the attached code:

Program.cs

using Microsoft.Extensions.Configuration;
using System;
using System.IO;
using System.Linq;

namespace EmptyCSharp
{
    public static class Program
    {
        public static void Main()
        {
            var configFilePath = $".{Path.DirectorySeparatorChar}config.json";

            var config = new ConfigurationBuilder()
                .AddJsonFile(configFilePath, false)
                .Build();

            Console.Write("Count of children: ");
            Console.WriteLine(config.GetChildren().Count());

            var section = config.GetSection("Export");
            Console.Write("Section is null?: ");
            Console.WriteLine(section == null);

            Console.Write("Value of Export:ServerAddress: ");
            try
            {
                Console.WriteLine(config["Export:ServerAddress"]);
            }
            catch
            {
                Console.WriteLine("Error accessing (value is null)");
            }

            Console.Write("Value of Export:Database: ");
            try
            {
                Console.WriteLine(config["Export:Database"]);
            }
            catch
            {
                Console.WriteLine("Error accessing (value is null)");
            }

            var val = config.GetValue<ExportConfig>("Export");

            Console.Write("Section value is null?: ");
            Console.WriteLine(val == null);

            Console.ReadKey();
        }
    }

    public class ExportConfig
    {
        public string ServerAddress { get; set; }

        public string Database { get; set; }
    }
}

config.json

{
  "Export": {
    "ServerAddress": "127.0.0.1",
    "Database": "asdff"
  }
}

[poke]

You want to do this instead:

var val = config.GetSection("Export").Get<ExportConfig>();

GetValue<T> binds a single configuration value at a specified path. But Export is not a path for a value; it is the path to a section that contains multiple values. But a section itself has no value (the value is null).

In order to (recursively) bind a section, you need to use Get<T> on the section. So that’s why the above code will work.