How to configure services based on request in ASP.NET Core

Question

In ASP.NET Core we can register all dependencies during start up, which executed when application starts. Then registered dependencies will be injected in controller constructor

Answer 1

I'm afraid you can not directly acheive the goal via simple dependency injection , as the the dependency injection configured at Startup stage , in other words , all services and implementions has been configured before a request comming .

However , you can inject a Create Service delegate so that can we create the required service implemention instance in runtime .

For instance , if we have a IReportFactory Interface and two implementions as blew :

public interface IReportFactory
{
    object Create();
}

public class ReportFactory1 : IReportFactory
{
    public object Create()
    {
        return new { F = 1, };
    }
}
public class ReportFactory2 : IReportFactory {
    public object Create()
    {
        return new { F = 2, }; 
    }
}

As we want to get the required implemention in future , we need to register the Implementions first .

services.AddScoped();
services.AddScoped();

and here's where the magic happens :

1. We don't register a IReportFactory

2. We just add a Func instead , which is a CreateReportFactoryDelegate

   public delegate IReportFactory CreateReportFactoryDelegate(Microsoft.AspNetCore.Http.HttpContext context);

We need add the CreateReportFactoryDelegate to servies too.

services.AddScoped(sp => {
    // return the required implemention service by the context;
    return context => {
        // now we have the http context ,
        // we can decide which factory implemention should be returned;
        // ...
        if (context.Request.Path.ToString().Contains("factory1")) {
            return sp.GetRequiredService();
        }
        return sp.GetRequiredService();
    };
});

Now , we can inject a CreateReportFactoryDelegate into controller :

public class HomeController : Controller
{
    private CreateReportFactoryDelegate _createReportFactoryDelegate;

    public HomeController(CreateReportFactoryDelegate createDelegate) {
        this._createReportFactoryDelegate = createDelegate;
        // ...
    }

    public async Task CacheGetOrCreateAsync() {

        IReportFactory reportFactory = this._createReportFactoryDelegate(this.HttpContext);
        var x=reportFactory.Create();

        // ...
        return View("Cache", cacheEntry);
    }
}