在ASP.NET Core中为服务和存储库层使用依赖注入的正确方法？

Question

I just learned the dependency injection system in ASP.NET Core RC1 . I have a controller (code below). Option 1 (the line commented out) I've used before. Option 2 would need to be repeated in each controller and is not preferred.

public class UserRegisterController : Controller
{
    private readonly IUserRegisterService _userRegisterService;
    private readonly UserManager<ApplicationUser> _userManager;
    public UserRegisterController(
        UserManager<ApplicationUser> userManager, 
        IOptions<WebAppSettings> settings,
        IUserRegisterService userRegisterService)
    {
        _userManager = userManager;
        // Option 2
        _userRegisterService = userRegisterService;
        // Option 1
        //_userRegisterService = 
        //    new UserRegisterService(
        //        new ActiveDirectoryRepository(settings.Value.ContainerDomain));
    }
}

internal class UserRegisterService : IUserRegisterService
{
    private readonly IActiveDirectoryRepository _repoAd;

    internal UserRegisterService(IActiveDirectoryRepository repoAd)
    {
       _repoAd = repoAd;
    } 
}

internal class ActiveDirectoryRepository : IActiveDirectoryRepository
{
    private readonly string _container;

    public ActiveDirectoryRepository(string container)
    {
        _container = container;
    }
}

In the Startup.cs\\Configure\\ConfigureServices we have the following.

Option 1:

services.AddTransient<Admin.Interfaces.IActiveDirectoryRepository, 
                      Admin.Repositories.ActiveDirectoryRepository>();
services.AddTransient<Admin.Interfaces.IUserRegisterService, 
                      Admin.Services.UserRegisterService>();

Option 2:

services.AddTransient<Admin.Interfaces.IActiveDirectoryRepository, 
                      Admin.Repositories.ActiveDirectoryRepository>();
services.AddTransient<Admin.Interfaces.IUserRegisterService, 
                      Admin.Services.UserRegisterService>(provider =>
                          new UserRegisterService(
                              new ActiveDirectoryRepository(
                                  Configuration["ContainerDomain"])));

Is option 2 the preferred implementation? I want to avoid using a third-party library for dependency injection. I think for my needs the standard means ASP.NET Core DI should be sufficient.

Answer 1

My preference would be to set it up as follows:

public class UserRegisterController : Controller
{
    private readonly UserManager<ApplicationUser> _userManager;
    private IUserRegisterService _userRegisterService;

    public UserRegisterController(
        UserManager<ApplicationUser> userManager,
        IOptions<WebAppSettings> settings,
        IUserRegisterService userRegisterService)
    {
        _userManager = userManager;
        _userRegisterService = userRegisterService;

    }

    //...
}

internal class UserRegisterService : IUserRegisterService
{
    private readonly IActiveDirectoryRepository _repoAd;

    public UserRegisterService(IActiveDirectoryRepository repoAd)
    {
        _repoAd = repoAd;
    }

}

internal class ActiveDirectoryRepository : IActiveDirectoryRepository
{
    private readonly string _container;

    public ActiveDirectoryRepository(IOptions<WebAppSettings> settings)
    {
        _container = settings.Value.ContainerDomain;
    }

}

public class WebAppSettings
{
    public string ContainerDomain { get; set; }

}

 public void ConfigureServices(IServiceCollection services)
    {
        services.AddOptions();
        services.Configure<WebAppSettings>(Configuration);

        // Add framework services.
        services.AddMvc();

        services.AddTransient<IActiveDirectoryRepository, ActiveDirectoryRepository>();
        services.AddTransient<IUserRegisterService, UserRegisterService>();
    }

this way you have your IUserRegisterService get automatically injected with the IActiveDirectoryService anytime you resolve the IUserRegisterService. The IActiveDirectoryService automatically gets injected with your WebAppsettings, where it can get it's config value. If everything is pre-wired like this then you only need to request that an instance of IUserRegisterService be injected into your controller.

Answer 2

Is option 2 more preferable?

No! We should use the ConfigureServices of option 1, but we will fix the issue you're having. With DI, if you find yourself attempting to use the new keyword -- stop, take a deep breath and reevaluate what you're trying to achieve.

You should use dependency injection throughout, it's all or nothing. Instead of having the ActiveDirectoryRepository .ctor take a string as a parameter, have it take on the IOptions<WebAppSettings> instead. This is part of the standard ASP.NET Core dependency injection and is preferred.

---

Let's review what you'd end up with in each...

First, the ActiveDirectoryRepository as I described above. The _container variable is set from the settings as desired.

internal class UserRegisterService : IUserRegisterService
{
    private readonly IActiveDirectoryRepository _repoAd;

    internal UserRegisterService(IActiveDirectoryRepository repoAd)
    {
        _repoAd = repoAd;
    }
}

Next, the UserRegisterService implementation can stay exactly as you have it now.

public class UserRegisterController : Controller
{
    private readonly IUserRegisterService _userRegisterService;
    private readonly UserManager<ApplicationUser> _userManager;

    public UserRegisterController(
        UserManager<ApplicationUser> userManager,
        IUserRegisterService userRegisterService)
    {
        _userManager = userManager;
        _userRegisterService = userRegisterService;    
    }
}

Finally, your UserRegisterController is simplified as follows:

 public class UserRegisterController : Controller { private readonly IUserRegisterService _userRegisterService; private readonly UserManager<ApplicationUser> _userManager; public UserRegisterController( UserManager<ApplicationUser> userManager, IUserRegisterService userRegisterService) { _userManager = userManager; _userRegisterService = userRegisterService; } } 

Notice, we no longer need the IOptions<WebAppSettings> here? This is a good thing as the options were only being used for something unrelated to this controller specifically.