.Net Core WebApi Dependency Injection

Question

I have a solution and I have different projects in it. One of them is the api project and I want to use dependency injection in this project, but I get the following error:

Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: CCM.Business.Abstract.ICompanyService Lifetime: Scoped ImplementationType: CCM.Business.Concrete.CompanyManager': Unable to resolve service for type 'CCM.DataAccess.Concrete.CompanyDal' while attempting to activate 'CCM.Business.Concrete.CompanyManager'.)

Startup.cs:

        public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers();

        services.AddScoped<ICompanyDal, CompanyDal>();

        services.AddScoped<ICompanyService, CompanyManager>();
        
        
    }

ICompanyDal:

    public interface ICompanyDal: IGenericDal<Company>
{
}

CompanyDal:

    public class CompanyDal:GenericDal<Company,CCMContext>,ICompanyDal
{
}

ICompanyService:

    public interface ICompanyService
{
    Company GetById(int id);
    List<Company> GetAll();
    void Create(Company entity);
    void Update(Company entity);
    void Delete(Company entity);
}

CompanyManager:

public class CompanyManager : ICompanyService
{
    private CompanyDal _companyDal;
    public CompanyManager(CompanyDal companyDal)
    {
        _companyDal = companyDal;
    }

    public void Create(Company entity)
    {
        _companyDal.Create(entity);
    }

    public void Delete(Company entity)
    {
        _companyDal.Delete(entity);
    }

    public List<Company> GetAll()
    {
        return _companyDal.GetAll();
    }

    public Company GetById(int id)
    {
        return _companyDal.GetById(id);
    }

    public void Update(Company entity)
    {
        _companyDal.Update(entity);
    }
}

Is there anything else I should pass on to you? please help.

Answer 1

In startup, you add the service ICompanyDal with the implementation CompanyDal. But in CompanyManager, you inject the implementation CompanyDal, not the service ICompanyDal.

Solution, inject the service in the constructor :

public class CompanyManager : ICompanyService
{
    private ICompanyDal _companyDal;
    public CompanyManager(ICompanyDal companyDal)
    {
        _companyDal = companyDal;
    }
...

Answer 2

Change the CompanyManager to explicitly depend on the registered abstraction

CompanyManager:

//...

private ICompanyDal _companyDal;
//CTOR
public CompanyManager(ICompanyDal companyDal) {
    _companyDal = companyDal;
}

//...

since that is what was registered with the container

Startup:

//...

services.AddScoped<ICompanyDal, CompanyDal>();

//...

Make sure that your controller(s) follow a similar format and explicitly depends on the registered abstraction(s) as well

Controller:

//...

public MyController(ICompanyService service) {
    //...
}

//...