How to resolve dependency in Web API constructor in .net core

Question

I am new to .net core and dependency injection concept. I want to inject service interface in Web API constructor, Service interface and implementation is in different project. Please find below layers of my application,

In startup.cs, I already add below line,

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddMvc();

    services.AddSingleton<IEntriesService, EntriesService>();
}

My controller,

public class EntriesController : Controller
{
    IEntriesService entryService;
    public EntriesController(IEntriesService _entryService)
    {
        entryService = _entryService;
    }

    // GET: api/values
    [HttpGet]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2" };
    }
}

Problem is, When I execute my API application, It is not hitting to my constructor and shows me blank page as below,

Without adding constructor, Application is working fine.

My IEntriesService,

public interface IEntriesService
{
    RepeatEntries Get(int Id);
}

My EntriesService,

public class EntriesService : IEntriesService
{
    IUnitOfWork _unitOfWork;
    public EntriesService(IUnitOfWork unitOfWork)
    {
        _unitOfWork = unitOfWork;
    }

    public bool Add(RepeatEntries entity)
    {
        _unitOfWork.EntryRepository.Add(entity);
        return true;
    }
}

My IUnitOfWork,

public interface IUnitOfWork : IDisposable
{
    IEntriesRepository EntryRepository { get; }
    void Complete();
}

My UnitOfWork,

public class UnitOfWork : IUnitOfWork
{
    private readonly IEntriesRepository _entryRepository;
    public UnitOfWork(IEntriesRepository entryRepository)
    {
        _entryRepository = entryRepository;
    }

    public IEntriesRepository EntryRepository
    {
        get
        {
            return _entryRepository;
        }
    }

    void IUnitOfWork.Complete()
    {
        throw new NotImplementedException();
    }

    #region IDisposable Support
    private bool disposedValue = false; // To detect redundant calls



    protected virtual void Dispose(bool disposing)
    {
        if (!disposedValue)
        {
            if (disposing)
            {
                // TODO: dispose managed state (managed objects).
            }

            // TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
            // TODO: set large fields to null.

            disposedValue = true;
        }
    }

    // TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
    // ~UnitOfWork() {
    //   // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
    //   Dispose(false);
    // }

    // This code added to correctly implement the disposable pattern.
    void IDisposable.Dispose()
    {
        // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
        Dispose(true);
        // TODO: uncomment the following line if the finalizer is overridden above.
        // GC.SuppressFinalize(this);
    }
    #endregion
}

What else I need to add to make it work? Is it possible or I need to change my approach?

500 is internal server error. Just hit F5 (start with debugging) and see what's the exception. Your approach is correct and there is no reason not to work. — regnauld
– regnauld, Commented May 1, 2017 at 11:49
Debugger is hitting to program and startup classes, But not to controller constructor. And refresh showing same page. — Keval Patel
– Keval Patel, Commented May 1, 2017 at 11:54
You need to provide more information if you expect us to help you without utilizing our all-mighty fortune-telling skills. You have only posted contents of your controller, but what about your EntriesService? We have no idea if it has any dependencies on its own and if you have registered them or not — Tseng
– Tseng, Commented May 1, 2017 at 12:03
The problem might be in your Startup class this is why it doesn't hit your controller. You can add a diagnostic middleware in the beginning of your pipeline so every time there is an unhandled exception you will see an exception page with details and stacktrace. To do this add nuget package to your project Microsoft.AspNetCore.Diagnostics and then add app.UseDeveloperExceptionPage() in the beginning of Startup.Configure() method. Hopefully this will give you more details on what is going on. — Alexey Andrushkevich
– Alexey Andrushkevich, Commented May 1, 2017 at 12:09
Do you register IUnitOfWork for DI somewhere ? If not, you should, otherwise MVC cannot build the hierarchy. — regnauld
– regnauld, Commented May 1, 2017 at 12:13

Nkosi · Accepted Answer · 2017-05-01 12:44:42Z

3

You have to register all dependencies with the composition root, making sure to register them with the correct lifetime i.e:(Scoped, Transient, Singleton) to avoid problems in future.

public void ConfigureServices(IServiceCollection services) {
    // Add framework services.
    services.AddMvc();

    services.AddSingleton<IEntriesService, EntriesService>();
    services.AddTransient<IUnitOfWork, UnitOfWork>();
    services.AddTransient<IEntriesRepository, EntriesRepository>();
    services.AddSingleton<IConnectionFactory, ConnectionFactory>();

    //...add other dependencies. 
}

Take some time and check out the documentation:

Introduction to Dependency Injection in ASP.NET Core

edited May 1, 2017 at 12:44

answered May 1, 2017 at 12:21

Nkosi

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