ASP.NET Core DI different options instance depending on requesting class

Question

I've used Autofac in the past and while sometimes it can be a bit complicated it has never lacked in features I needed. Now I'm trying to use the built-in dependency injection in ASP.NET Core and am having trouble achieving the following:

Startup.cs

public void ConfigureServices(IServiceCollection services) {
  // Use these settings by default
  services.Configure<EmailerSettings>(Configuration.GetSettings("DefaultEmailer"));

  // Would like to specify different settings that apply to the SpecialEmailer class only
  //services.Configure<EmailerSettings>(Configuration.GetSettings("SpecialEmailer"));
}

Classes that depend on DI

public class Emailer {
    public Emailer(IOptions<EmailerSettings> settings) {
       // Should get the default settings
    }
}

public class SpecialEmailer {
    public SpecialEmailer(IOptions<EmailerSettings> settings) {
       // Should get the special settings
    }
}

Is there any way to do this with the out of the box DI? I could of course create SpecialEmailerSettings and use that in the SpecialEmailer class, but the structure is identical so I'd like to reuse if possible.

Answer 1

There are several ways to do that, but I don't think that any of them is elegant as you're hoping for. I guess your best bet is to create another settings model SpecialEmailerSettings that inherits from EmailerSettings . I know that you've already thought of this and you wanted to reuse, but I think inheritance is one way of reusing. It's just one extra line:

public class SpecialEmailerSettings : EmailerSettings { }

Then load it like this:

services.Configure<EmailerSettings>(Configuration.GetSettings("DefaultEmailer"));
services.Configure<SpecialEmailerSettings>(Configuration.GetSettings("SpecialEmailer"));

And finally use it in your class:

public class SpecialEmailer {
    public SpecialEmailer(IOptions<SpecialEmailerSettings> settings) {
       // Should get the special settings
    }
}