如何在 ASP.Net Core 服务层的基础 class 中获取当前用户？

Question

There are answers how to get User principal in service layer using IHttpContextAccessor but they are always related to getting the user in service itself, not in its base (abstract class).

I have following situation:

There is an UserService which is injected in controller which needs it like this:

private IUserService UserService;
public UserController(IUserService userService)
{
    UserService = userService;
}

Pretty standard, this is service layer for getting/posting/patching... user. Problem is, this UserService inherits something called ServiceBase :

public class UserService : ServiceBase, IUserService
{
    private IDatabaseService DatabaseService;
    public UserService(IDatabaseService databaseService, ServiceManager serviceManager) : base(serviceManager)
    {
        DatabaseService = databaseService;
    }
.. rest of code omitted ...

and ServiceBase looks like this:

public abstract class ServiceBase
{
    internal static readonly NLog.Logger log = NLog.LogManager.GetCurrentClassLogger();
    private ServiceManager ServiceManager;

    public ServiceBase(ServiceManager serviceManager)
    {
        ServiceManager = serviceManager;
    }
 ... rest of code omitted...

Now, if I wanted to use IHttpContextAccessor I would have to inject it in each of services so it can be passed to ServiceBase , much like ServiceManager (another singleton service, not related to this question) is passed to it. Reason why ServiceBase is needed is for logging and more importantly, providing a way for each of services to post changes made by them (post, patch, delete) to rest of microservices.

Startup looks like this:

 services.AddSingleton<ServiceManager>();
 services.AddHostedService(provider => provider.GetService<ServiceManager>());

 services.AddHttpContextAccessor();
 services.AddScoped<IDatabaseService, DatabaseService>();
 services.AddScoped<ILoginService, LoginService>();
 services.AddScoped<IUserService, UserService>();

Is there a way to get IHttpContextAccessor in this ServiceBase without passing it around? Same question could be asked for ServiceManager since that dependancy also has to be passed from implementation to base class? What I want is to know which user did call the controller action (and consequently the service layer) without writing bunch of boilerplate code in each of controllers and/or services.

Another way of asking would be is it possible to resolve singleton services like IHttpContextAccessor and ServiceManager inside service layer without injecting them in each service?

Answer 1

Short answer: You can't.

Bad answer: You shouldn't. But you can with a ServiceLocator .

Alternate answer: we can make the paramter transfer less pain.

Instead of passing ServiceManager to the base class, pass a ServiceBaseServiceContext to it:

public class ServiceBaseServiceContext
{
    public ServiceManager ServiceManager {get;}
    public IUserService UserService {get;}

    public ServiceBaseServiceContext(ServiceManager serviceManager, IUserService userService)
    {
        ServiceManager = serviceManager;
        UserService = userService;
    }
}

This way, you have only one Parameter, regardless how many services you need.

public abstract class ServiceBase
{
    private ServiceManager _serviceManager;
    private IUserService_userService;

    public ServiceBase(ServiceBaseServiceContext serviceContext)
    {
        _serviceManager = serviceContext.ServiceManager;
        _userService = serviceContext.UserService;
    }
}

ServiceBaseServiceContext needs also to be registered in your ServiceCollection to make it work:

// depending on the services maybe Scoped
services.AddTransient<ServiceBaseServiceContext>();

Instead of making a ServiceBaseServiceContext you could also pass a IServiceProvider to ServiceBase , but this would be the same as a ServiceLocator, which is bad, because it hides the dependencies.