ASP.NET Core appsettings.json update in code

Question

I am currently working on project using asp.net core v1.1, and in my appsettings.json I have:

"AppSettings": {
   "AzureConnectionKey": "***",
   "AzureContainerName": "**",
   "NumberOfTicks": 621355968000000000,
   "NumberOfMiliseconds": 10000,
   "SelectedPvInstalationIds": [ 13, 137, 126, 121, 68, 29 ],
   "MaxPvPower": 160,
   "MaxWindPower": 5745.35
},

I also have class that I use to store them:

public class AppSettings
{
    public string AzureConnectionKey { get; set; }
    public string AzureContainerName { get; set; }
    public long NumberOfTicks { get; set; }
    public long NumberOfMiliseconds { get; set; }
    public int[] SelectedPvInstalationIds { get; set; }
    public decimal MaxPvPower { get; set; }
    public decimal MaxWindPower { get; set; }
}

And DI enabled to use then in Startup.cs:

services.Configure<AppSettings>(Configuration.GetSection("AppSettings"));

Is there any way to change and save MaxPvPower and MaxWindPower from Controller?

I tried using

private readonly AppSettings _settings;

public HomeController(IOptions<AppSettings> settings)
{
    _settings = settings.Value;
}

[Authorize(Policy = "AdminPolicy")]
 public IActionResult UpdateSettings(decimal pv, decimal wind)
 {
    _settings.MaxPvPower = pv;
    _settings.MaxWindPower = wind;

    return Redirect("Settings");
 }

But it did nothing.

Answer 1

Here is a relevant article from Microsoft regarding Configuration setup in .Net Core Apps:

Asp.Net Core Configuration

The page also has sample code which may also be helpful.

Update

I thought In-memory provider and binding to a POCO class might be of some use but does not work as OP expected.

The next option can be setting reloadOnChange parameter of AddJsonFile to true while adding the configuration file and manually parsing the JSON configuration file and making changes as intended.

    public class Startup
    {
        ...
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }
        ...
    }

... reloadOnChange is only supported in ASP.NET Core 1.1 and higher.

Answer 2

Basically you can set the values in IConfiguration like this:

IConfiguration configuration = ...
// ...
configuration["key"] = "value";

The issue there is that e.g. the JsonConfigurationProvider does not implement the saving of the configuration into the file. As you can see in the source it does not override the Set method of ConfigurationProvider. (see source)

You can create your own provider and implement the saving there. Here (Basic sample of Entity Framework custom provider) is an example how to do it.

Answer 3

Suppose appsettings.json has an eureka port, and want to change it dynamically in args (-p 5090). By doing this, can make change to the port easily for docker when creating many services.

  "eureka": {
  "client": {
    "serviceUrl": "http://10.0.0.101:8761/eureka/",
    "shouldRegisterWithEureka": true,
    "shouldFetchRegistry": false 
  },
  "instance": {
    "port": 5000
  }
}


   public class Startup
   {
    public static string port = "5000";
    public Startup(IConfiguration configuration)
    {
        configuration["eureka:instance:port"] = port;

        Configuration = configuration;
    }


    public static void Main(string[] args)
    {
        int port = 5000;
        if (args.Length>1)
        {
            if (int.TryParse(args[1], out port))
            {
                Startup.port = port.ToString();
            }

        }
     }