Adding a custom provider to Asp.Net Core

Question

I have the following code in my Program.cs:

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)            
        .ConfigureAppConfiguration(b => b
            .AddEnvironmentVariables()
            .AddMyCustomConfiguration(o => o.UseSqlServer(
                Environment.GetEnvironmentVariable("ConnectionStrings:MyDatabase"))))                
        .UseStartup<Startup>();

My appsettings.json looks like this:

{
  "ConnectionStrings": {
    "MyDatabase": "connectionstring"
  }
}

However, Environment.GetEnvironmentVariable("ConnectionStrings:MyDatabase") is returning null. I was under the impression that AddEnvironmentVariables would load the necassary variables. Is this not the case / how can I get this to load the connection string?

Edward · Accepted Answer · 2019-09-16 07:17:28Z

1

For getting ConnectionStrings from appsettings.json, you should use GetConnectionString instead of reading environment.

Try something like below:

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)            
    .ConfigureAppConfiguration(b => {
            b.AddEnvironmentVariables();
            var connectionString = b.Build().GetConnectionString("MyDatabase");
            .AddMyCustomConfiguration(o => o.UseSqlServer(connectionString));
    })              
    .UseStartup<Startup>();

answered Sep 16, 2019 at 7:17

Edward

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3 Comments

user11409100 Over a year ago

This still returns null

Edward Over a year ago

@CuriousDev Is there any demo to reproduce your issue?

Sukanta Over a year ago

Thank you for this @Edward, It works!!!! I think OP didn't realize .Build() part of it

Pedro Brito · Accepted Answer · 2019-09-12 10:56:38Z

0

See this example

 public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
WebHost.CreateDefaultBuilder(args)
  .ConfigureAppConfiguration((hostingContext, config) =>
  {
    var env = hostingContext.HostingEnvironment;

    config.AddJsonFile("application.json", optional: false, reloadOnChange: true);
    config.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
    config.AddEnvironmentVariables("ASPNETCORE_");
    config.AddCommandLine(args);
  })
  .UseStartup<Startup>();

here you have the link to the article https://www.johanohlin.com/blog/configuration-providers-in-aspnet-core/

answered Sep 12, 2019 at 10:56

Pedro Brito

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1 Comment

user11409100 Over a year ago

This doesn't make any difference. I've tried various combinations on the approach, but no luck. Obviously AddEnvironmentVariables("ASPNETCORE_") is no good to me, so I just load them all

Yury Schkatula · Accepted Answer · 2019-09-12 13:16:35Z

0

You've put your settings into JSON config, not into env var(s). This is why GetEnvironmentVariable() returns nothing. And ASP.Net Core is not intended to export your config to env vars unless you did that explicitly (let say, via SetEnvironmentVariable() or an equivalent).

If you actually intend to just read a connection string value, take a look on this topc How to read connection string in .NET Core?

answered Sep 12, 2019 at 13:16

Yury Schkatula

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