Global Variables in ASP.Net Core 2

I often do this kind of thing with connection strings and other global constants. First create a class for those variables that you need. In my project it is MDUOptions but whatever you want.

public class MDUOptions
{
    public string mduConnectionString { get; set; }
    public string secondaryConnectionString { get; set; }
}

Now in your Startup.cs ConfigureServices method:

Action<MDU.MDUOptions> mduOptions = (opt =>
{
    opt.mduConnectionString = Configuration["ConnectionStrings:mduConnection"];
});
services.Configure(mduOptions);
services.AddSingleton(resolver => resolver.GetRequiredService<IOptions<MDUOptions>>().Value);

Now you use DI to access it in code:

public class PropertySalesRepository : IPropertySalesRepository
{
    private static string _mduDb;

    public PropertySalesRepository(MDUOptions options)
    {
        _mduDb = options.mduConnectionString;
    }
    ....
}

In my case the only property I wanted was the string but I could have used the entire options class.

In appsettings.json keep the variables.

{
    "foo": "value1",
    "bar": "value2",
}

Create AppSettings class.

public class AppSettings
{
    public string foo { get; set; }

    public string bar { get; set; }
}

In Startup.cs file register.

public IServiceProvider ConfigureServices(IServiceCollection services)
{
    services.Configure<AppSettings>(Configuration);
}

Usage,

public class MyController : Controller
{
    private readonly IOptions<AppSettings> _appSettings;

    public MyController(IOptions<AppSettings> appSettings)
    {
        _appSettings = appSettings;
    }
    var fooValue = _appSettings.Value.foo;
    var barValue = _appSettings.Value.bar;
}