Injecting Dependency in Method in ASP.NET Core

Question

I have the following scenario: I got a service ICompanyDocumentsService with a single implementation CompanyDocumentsServicewhich I register in my Startup class:

 public void ConfigureServices(IServiceCollection services)
        {
            services.AddScoped<ICompanyDocumentService, CompanyDocumentService>();
        }

I need this service in many places, and it doesn't bother me using DI in Constructor. However, there is one place where I need it injected in a Method (or probably in a property would be even better):

            public abstract class CompanyDocumentBase
            {
                public abstract object GetAllProperties(Employee employee, string properties, 
                      CompanyDocumentReferenceData documentReferenceData);
                // blah, blah, lots of Formatting Methods


                private CompanyDocumentService CompanyDocumentService { get; set; } // **inject service here**

                public string GetFormattedEmployeeIndividualEmploymentAgreementNumber(Employee employee, 
                    ICompanyDocumentService companyDocumentService = null) // **optional because 
//inherited class doesn't need to know anything about this service, it concerns only it's result**
                {
                    companyDocumentService = CompanyDocumentService;
                    var test  = 
                       companyDocumentService.GetEmloyeeIndividualEmploymentAgreementNumber(employee.Id);


                    return string.Empty;
                }

            }

There are many classes inheriting CompanyDocumentBase which are only concerned in it's method results, as mentioned above, that's why that parameter is optional, and that's why I don't need injecting DI in constructor, thus the inheriting classes won't be needing that.

 public class JobDescriptionCompanyDocument : CompanyDocumentBase
    {
        public override object GetAllProperties(Employee employee,
            string properties, CompanyDocumentReferenceData documentReferenceData)
        {
            var document = JsonConvert.DeserializeObject<JobDescriptionModel>(properties);

            document.IndividualEmploymentAgreementNumber = GetEmployeeIndividualEmploymentAgreementNumber(employee);

            return document;
        }
    }

Is there any simple way to achieve this? Preferable without needing to install a separate library like Unity or Autofac. Ideal it would be to somehow get the instance of CompanyDocumentsService directly into that property, something like:

private CompanyDocumentService CompanyDocumentService => Startup.Services.blah that instance

Answer 1

One hack way (personally I wouldn’t recommend it), is after your container is built, you could resolve an instance of IHttpContextAccessor and set it to static class, e.g. IoC

Then you could do private CompanyDocumentService CompanyDocumentService => IoC.HttpContextAccessor.HttpContext.RequestServices.GetService().

https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.httpcontext.requestservices?view=aspnetcore-3.1

The interface is a singleton, and provides access to scoped services from a static context.

Note you might have to explicitly register HttpContextAccessor: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/http-context?view=aspnetcore-3.1

UPDATE

What I'd recommend

If you are open to object factories, and changing the way how DocumentBase is instantiated, try make a factory, and whenever you need an instance of DocumentBase, only use the factory to create it:

public abstract class CompanyDocumentBase
{
    // Use internal so that access only limited to friendly assembly
    internal CompanyDocumentService CompanyDocumentService { get; set; }
}

// Inject this class to where you need to create an instance of CompanyDocumentBase
public class CompanyDocumentFactory<T> where T : CompanyDocumentBase
{
    private readonly IServiceProvider _services;

    // DI contaiener has implicit IServiceProvider support, when you do this on constructor, it injects service provider of *current* scope
    // If this factory is registered as singleton, you need to use IHttpContextAccessor to use request's service provider in Create method
    // because your DocumentService is scoped.
    public CompanyDocumentFactory(IServiceProvider services)
    {
        _services = services;
    }

    public T Create()
    {
        // Create an instance of document use your current method.
        var instance = new T();
        instance.CompanyDocumentService = _services.GetRequiredService<ICompanyDocumentService>();
        return instance;
    }
}