How to keep settings in ASP.NET Core? -

How to keep settings in ASP.NET Core?

I’m not a big enthusiast of hard-coded values in my apps, mostly because of three things. First, it’s really annoying to change their value if necessary (especially if one is used in many places). Of course, we can use some “find and replace tool” but to be honest I don’t fully trust them. Another thing is that in many cases we have absolutely no idea what do they represent. Let’s say we have the following of code:


PaymentService.Create(order, "1267899567");


What does the second parameter represent? Is that some API key, client secret for hashing, or maybe it’s an invoice number? Who knows. Last disadvantage of such approach is that changing the hard-coded value requires all the code (or more precisely, assembly wich contains changed code) to be recompiled before deploying to the server. We can’t simply change and save it. That’s why I’d suggest using always some sort of configuration file. Fortunately doing that with ASP.NET Core is really simple to configure and use! And that’s what I’m going to present right now 🙂


Configuring ASP.NET Core app

Let’s say that we’d like to extract some payment data to the configuration file. The data would be:

  • SecretKey (string)
  • ClientId (int)

The C# class created for that purpose looks as follows:


public class PaymnetSettings
    public string SecretKey { get; set; }

    public int ClientId { get; set; }


Now, or the first step is to create a dedicated section inside the appsettings.json file with values:


  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
  "PaymentSettings": {
    "SecretKey": "It's super secret!",
    "ClientId":  "2675"


Having this we can now move to the Startup class or our application. Inside ConfigureServices method we need to add the following line:




Believe or not – that’s all we need to do! Having the model registered we can now inject it inside some class. I’ll do this inside default WebAPI ValueController:


public class ValuesController : Controller

    public ValuesController(IOptions<PaymnetSettings> settings)
        var paymentSettings = settings.Value;
    public IEnumerable<string> Get()
        return new string[] { "value1", "value2" };



Notice that the only difference is that we had to inject PaymentSettings wrapped by IOptions interface. Comparing to the hard-coded values, this one has a lot of advantages:

  • changing the value requires the action only in one place
  • those values are naturally encapsulated and named inside dedicated classes, so it’s much easier to understand their meaning
  • we can change the value of each parameter having the app running on the server without the need to redeploying it

Hope, that it will help some of you in the future 😉

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