WebApi to Service & Service to Repository pattern with dependency injection but limited references

Question

I am refactoring an existing dotnet core application where in short we have a

• WebApi project
• Business (services) project
• Repositories project
• Datalayer project

Currently, in our webapi project, all other three projects are referenced. This implies also that in controllers, repos and services are injected and used in the controller actions.

I was in the understanding that in Controllers, we only should call services and the service would call the repositories and the repository should use the datalayer.

I am trying to refactor all of this but i want to get rid of the dependency in the WebApi project towards repository project and datalayer project.

The problem is then, when a service is called, the repos and further on the datalayer is not found anymore for further injection.

Am i totally mistaken in my setup i want ? How can I solve this so that for references i have

• WebApi only references Business
• Business only references Repositories
• Repositories only references DataLayer

But i want my DI to keep on working as expected.

Am i expecting the impossible or am i totally confused? Thank to enlighten me.

Answer 1

In my opinion, your project references are correct.

For example, if there are 3 layers, Controllers, BLL, and DAL, they should be referenced like this: Controllers -> BLL -> DAL.

I think, there could be some problem with DI settings. For instance, in one of my projects I have Contollers project (Presentation layer) with reference to the BLL project. So, the DI for Controllers looks like:

file: Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    // Some settings go here ... 
    MapsterConfig.MapsterSetup();
    services.AddControllers();
    

   // And here I add the DI for the BLL project.
    services.AddBllInfrastructure(Configuration);
}

In the BLL project, there is a DependencyInjection.cs class:

public static class DependencyInjection
{
    public static void AddBllInfrastructure(this IServiceCollection services, IConfiguration configuration)
    {
        MapsterConfig.MapsterSetup();

        services.AddDbContext<MyDbContext>(options =>
            options.UseNpgsql(configuration.GetConnectionString("DefaultConnection"), x => x.UseNetTopologySuite()));

        // Repositories, come from the DAL project
        services.AddScoped<IMyDbContext, MyDbContext>();
        services.AddScoped<IUnitOfWork, UnitOfWork>();

        // Services, located in the BLL project
        services.AddTransient<IService1, Service1>();
        services.AddTransient<IService2, Service2>();
}

This way it works for me, hope this helps.