Custom Dependency injection in .NET 7

Question

Hello all,

I have come across a scenario in our application where I have to initialize my services project with a URL. Earlier the URL was stored in configuration so we could pass the configuration variable while adding the services.
e.g.
builder.Services.AddTransient<Iservice,GethirdpartyServiceUrl(url from config)>

Now as per the new requirement, the users first need to select the url where they want to connect. So we need to pass the url from the application instead of configuration.

How can I initialize the services and intialize the service once user has selected an url?

I tried to create a middleware and passed the Servicecollection in middleware and inject the url from session. It fails with below error
InvalidOperationException: The service collection cannot be modified because it is read-only.

Could you please suggest a solution ?

Answer 1

Use a factory pattern. The factory lets you activate a service per request. Store the URL in a database table and fetch the URL during the request.

Dependency injection in ASP.NET Core

Dependency injection guidelines

Answer 2

Hi, @Amit Dimri

From your description, I think you can create an enum model contains all the Url which user need to select, Then use factory pattern to create your service. Here is a simple demo, Hope it can help you solve this issue.

public enum MyUrl
    {
		//some url which user need
        UrlAAA,
        UrlBBB,
    }

service

public interface IMyService
    {
        string getUrl();
    }

I'm assuming that each url has a different use, so I create instances for them all.

public class MyServiceUrlB : IMyService
    {
        public string getUrl()
        {
            return "UrlBBB";
        }
    }

public class MyServiceUrlA : IMyService
    {
        public string getUrl()
        {
            return "UrlAAAAA";
        }
    }

factory pattern interface and instance

public interface IMyServiceFactory
    {
        public IMyService GetUrl(MyUrl url);
    }

public class MyServiceFactory : IMyServiceFactory
    {
        private readonly IServiceProvider _serviceProvider;

        public MyServiceFactory(IServiceProvider serviceProvider)
        {
            _serviceProvider = serviceProvider;
        }

        public IMyService GetUrl(MyUrl url)
        {
            switch (url)
            {
                case MyUrl.UrlAAA:
                    return (IMyService)_serviceProvider.GetService(typeof(MyServiceUrlA));
                case MyUrl.UrlBBB:
                    return (IMyService)_serviceProvider.GetService(typeof(MyServiceUrlB));
                default:
                    throw new ArgumentOutOfRangeException(nameof(url), url, $"Shape of {url} is not supported.");
            }
        }
    }

Register them in program.cs file

builder.Services.AddTransient<IMyServiceFactory, MyServiceFactory>();
builder.Services.AddScoped<MyServiceUrlA>().AddScoped<IMyService, MyServiceUrlA>(s => s.GetService<MyServiceUrlA>());
builder.Services.AddScoped<MyServiceUrlB>().AddScoped<IMyService, MyServiceUrlB>(s => s.GetService<MyServiceUrlB>())

register in controller

public class HomeController : Controller
    {
        //......
        private readonly IMyServiceFactory _myServiceFactory;
        

        public HomeController(IMyServiceFactory myServiceFactory)
        {
            _myServiceFactory = myServiceFactory;
        } 

        public string Url(MyUrl url)
        {
            var urlservice = _myServiceFactory.GetUrl(url);
            var result =  urlservice.getUrl();
            return result;
        }
}

Now you can check it will initialize different service according to the url user select.

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