How do I use dll of .net 5 class library that contain in its class Dependency injection?

Question

In my Asp.net Core 5 API Project

I have a serviceLayer that the controller uses, to get data from a third layer called dataLayer. I want to use the service layer as a DLL in different projects.

This ServiceLayer Contain dependency Injections like that :

namespace ServiceLayer
{
    public class UserService :  IUserService
    {
        IUserRepository userRepository; // (From DataLayer)
        public UserService(IUserRepository repository) : base(repository)
        {
            this.userRepository = repository;
        }
        public Users GetAllPersonsById(int id)
        {
                return userRepository.GetById(id);
        }
    }

    public interface IUserService : IService<Users>
    {
        Users GetAllPersonsById(int id);
    }

How can I use the method GetAllPersonsById with the DLL ServiceLayer

ServiceLayer, is a class library. I want to use it in other project. my question about how can I use it because the dependency Injections — Ali.K, Oct 08 '21 at 12:33
Then import as a reference, the dependency injection is done in the DLL itself — Ermiya Eskandary, Oct 08 '21 at 12:36
If the class library is in the same solution as the app, just add it as a project reference (right-click References then Add References). If not, you'll have to create a nuget package. — GH DevOps, Oct 08 '21 at 12:58

score 1 · Answer 1 · answered Oct 08 '21 at 13:00

can I use it because the dependency Injections

As soon as you reference the DLL / project you can use all classes the same ways as if they were in the project.

To use a class as a service:

Provide the service
Inject the service

There's a lot of documentation available, so I'll keep this short:

// provide in startup.cs
services.AddTransient<IUserService, UserService>();

// Inject where you need it
MyConstructor(IUserService userService) {}

See https://learn.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection?view=aspnetcore-5.0

Provide Extension Method

If we take a look at other libs, most of them provide a method to setup the services.

Example: Entity framework core

public void ConfigureServices(IServiceCollection services)
{                    
    services.AddDbContext<MyDbContext>(options => options.UseSqlServer(...));
}

So you could:

In your lib, create an extension method for IServicesCollection that adds all services of your lib.
In the consuming project, call services.AddMyLibServices().

This could look like so:

public static class ServicesConfiguration
{
    public static void AddDataLayer(this IServiceCollection services)
    {
        services.AddTransient<IUserService, UserService>();
        // ... same for all services of your lib
    }

}

Here's a tutorial with more details: https://dotnetcoretutorials.com/2017/01/24/servicecollection-extension-pattern/

Lamar service registries

An optional and alternative approach are service registries. It's very similar to the extension methods but uses a class to do the setup. See https://jasperfx.github.io/lamar/documentation/ioc/registration/registry-dsl/

Composition Root

You may want to read about the composition root pattern, e.g. What is a composition root in the context of dependency injection?

In a simple app, your startup.cs is your composition root. In more complex apps, you could create a separate project to have a single place to configure your apps services.

Create the DLL

There are two ways to create the DLL:

As a project in your solution (so your solution has multiple projects, each will result in a separate DLL)
As a separate solution and as nuget package

How do I use dll of .net 5 class library that contain in its class Dependency injection?

1 Answers1

Provide Extension Method

Lamar service registries

Composition Root

Create the DLL