Getting null error when reading configuration from appsettings.json in asp.net core

Question

I created a simple ASP.NET Core 6 MVC application in which I am just reading values from the appsettings.json file.

In my appsettings, I created two sections SectionA and SectionB:

{
  "SectionA": {
    "SectionASubItem1": "test value",
    "SectionASubItem2": "test value2"
  },
  "SectionB": {
    "SectionBSubItem1": "test value",
    "SectionBSubItem2": "test value2"
  }
}

I also created a class to map this value with class properties:

This is what my MyConfiguration class looks like:

public class MyConfiguration
{
    public SectionA SectionA { get; set; }
    public SectionB SectionB { get; set; }
}

public class SectionA
{
    public string SectionASubItem1 { get; set; }
    public string SectionASubItem2 { get; set; }
}

public class SectionB
{
    public string SectionBSubItem1 { get; set; }
    public string SectionBSubItem2 { get; set; }
}

In the program.cs class I created a variable type of IConfigurationRoot in which I am storing the JSON file properties:

var myConfiguration = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
    .Build();

and mapping the section like this:

builder.Services.Configure<SectionA>(myConfiguration.GetSection("SectionA"));
builder.Services.Configure<SectionB>(myConfiguration.GetSection("SectionB"));

The problem is when I am reading the sectionA and sectionB inside the controller I am getting null. Due to this, I am not getting values from JSON file.

public readonly MyConfiguration configuration;

public WeatherForecastController()
{
    configuration = new MyConfiguration();
}

[HttpGet(Name = "GetWeatherForecast")]
public IActionResult Get()
{
    // Here I am getting null
    var sectionA = configuration.SectionA;

    if (sectionA == null)
        return BadRequest();

    return Ok();
}

Are you sure that the `new MyConfiguration()` in the controller's constructor returns the `myConfiguration ` object? — GoodboY, Jun 29 '22 at 20:29
Why are you doing this - `configuration = new MyConfiguration();`? Please read the documentation, especially [ASP.NET Core one](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/?view=aspnetcore-6.0) about configuration. — Guru Stron, Jun 29 '22 at 20:56

dimmits · Answer 1 · 2022-06-29T21:18:05.933

you can do this

in appsettings.json

 "test": {
        "MyConfiguration": {
          "SectionA": {
            "SectionASubItem1": "test value",
            "SectionASubItem2": "test value2"
          },
          "SectionB": {
            "SectionBSubItem1": "test value",
            "SectionBSubItem2": "test value2"
          }
        }
      }

in programm.cs

builder.Services.Configure<MyConfiguration>(myConfiguration.GetSection("test:MyConfiguration"));

and then

private readonly MyConfiguration _myConfiguration;

public WeatherForecastController(IOptions<MyConfiguration> options)
{
    _myConfiguration = options.Value;
}

var sectionA = _myConfiguration.SectionA; bla bla

it is better to use IOptions,IoptionsSnapshot, or IOptionsMonitor.

Difference between IOptionsMonitor vs. IOptionsSnapshot

score 0 · Accepted Answer · answered Jun 30 '22 at 02:26

Set your appsetting.json like this:

"MyConfiguration": {
    "SectionA": {
      "SectionASubItem1": "test value AAAAAA",
      "SectionASubItem2": "test value2 AAAA"
    },
    "SectionB": {
      "SectionBSubItem1": "test value BBBBBB",
      "SectionBSubItem2": "test value2 BBBBBB"
    }
  }

Then in Program.cs configure like this:

builder.Services.Configure<SectionB>(myConfiguration.GetSection("MyConfiguration"));

The most important point is don't new MyConfiguration() in your Constructor, you need to use dependency injection to set the value.

private readonly IOptions<MyConfiguration> _configuration;

public WeatherForecastController(IOptions<MyConfiguration> configuration)
{
    _configuration= configuration;
}

Then you can get the value in _configuration:

Getting null error when reading configuration from appsettings.json in asp.net core

2 Answers2