How to register this dependency in ASP.NET Core?

Question

public abstract class BaseClass<T> {
    private ISomeinterface _param;
    
    public BaseClass(ISomeinterface param) {
        _param = param;
    }
}

public class DerivedClass : BaseClass<Entity> {
    public DerivedClass(ISomeinterface param) : base(param) {}
}

How to register this dependency in ASP.NET Core?

Answer 1

AddScoped, AddTransient and AddSingleton methods receive a serviceType and and implementationType which both are passed as Type , at the end both are inserted on IServiceCollection Here is the implementation

private static IServiceCollection Add(
      IServiceCollection collection,
      Type serviceType,
      Type implementationType,
      ServiceLifetime lifetime)
    {
      ServiceDescriptor serviceDescriptor = new ServiceDescriptor(serviceType, implementationType, lifetime);
      collection.Add(serviceDescriptor);
      return collection;
    }

So answering your question, you can register a generic type as service, not as an implementation because you can't create an instance of a generic type. But based on your implementation you can't register your generic type without specifying on the implementation type the generic parameter. This should fail

services.AddScoped(typeof(BaseClass<>), typeof(DerivedClass));

with the following error:

Open generic service type 'BaseClass`1[T]' requires registering an open generic implementation type. (Parameter 'descriptors')

See the definitions below

public abstract class BaseClass<T>
{

    public BaseClass()
    {
    }
}

public class DerivedClass : BaseClass<Entity>
{
    public DerivedClass() : base() { }
}

public class DerivedClass2<T> : BaseClass<T> where T: Entity
{
   
}

public class Entity
{

}

Now this should work perfectly as well

services.AddScoped(typeof(BaseClass<>), typeof(DerivedClass2<>));

or

services.AddScoped(typeof(BaseClass<Entity>), typeof(DerivedClass2<Entity>));

Hope this helps