What is the difference between services.Configure() and services.AddOptions<T>().Bind() when loading configuration in ASP.NET Core?

Question

In my ASP.NET Core 2.2 WebApi project, I want to load configuration from appsettings.json into strongly typed object.

The appsettings.json has following configuration section:

{   "MySettings1": {     "Name": "John Smith",     "Age": "25",   } } 

which I want to load into strongly typed object MySettings:

public class MySettings {     public string Name { get; set; }     public int Age { get; set; } } 

I can do this in my Startup.ConfigureServices() method either like this:

services.Configure<MySettings>(configuration.GetSection("MySettings1")); 

or like this:

services.AddOptions<MySettings>().Bind(configuration.GetSection("MySettings1")); 

What is the difference between these two approaches? Both of them work fine as I am able to get proper instance of IOptions<MySettings> injected in HomeController in both cases.

Are there some specific scenarios in which I should use one over the other approach? (for example, in the future I will probably want to add some kind of runtime validation of the MySettings object once it's populated from the configuration, so in this case should I prefer one approach over the other?)

Answer 1

This was asked in a Github issue in November 2018 Question: AddOptions() vs. Multiple Configure(…). Both methods do the same job but AddOptions came later and allows more customizations.

Configure(Action configureOptions) and OptionsBuilder.Configure(Action configureOptions) will both end up doing the same thing:

services.AddSingleton<IConfigureOptions<TOptions>>(     new ConfigureNamedOptions<TOptions>(name, configureOptions)); 

And OptionsBuilder.Bind(IConfiguration config) will actually call Configure(IConfiguration config) directly, so they are also equivalent.

So both APIs are interchangeable. And you can expect the services.Configure calls to continue to work. The options builder API came later to allow for a bit more control with various utility methods. But it’s not a replacement for the direct services.Configure API.