EF 7 (Core). Create DBContext like AddTransient

问题

According to documents when I configure DbContext like below DI register it in scope (per http request)

services.AddEntityFramework()
   .AddSqlServer()
   .AddDbContext<DBData>(options => {
        options.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]);                    
    }
);

The problem appears when I am trying to access it in another thread.

public class HomeController : Controller
{
    private readonly DBData _context;

    public HomeController(DBData context)
    {
        _context = context;
    }

    public IActionResult StartInBackground()
    {
        Task.Run(() =>
            {
                Thread.Sleep(3000);
                //System.ObjectDisposedException here
                var res = _context.Users.FirstOrDefault(x => x.Id == 1);
            });

        return View();
    }
}

I want to configure DbContext creation per each call (AddTransition). It would give me possibility to write next code

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddEntityFramework()
            .AddSqlServer()
            .AddDbContext<DBData>(options => {
                //somehow configure it to use AddTransient
                options.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]);                    
                }
            );

        services.AddTransient<IUnitOfWorkFactoryPerCall, UnitOfWorkFactory>();
        services.AddScoped<IUnitOfWorkFactoryPerRequest, UnitOfWorkFactory>();

        services.AddMvc();
    }

    public interface IUnitOfWorkFactoryPerCall : IUnitOfWorkFactory { }
    public interface IUnitOfWorkFactoryPerRequest : IUnitOfWorkFactory { }

    public interface IUnitOfWorkFactory : IDisposable
    {
       DBData Context { get; }
    }

    public class UnitOfWorkFactory : IUnitOfWorkFactoryPerCall, IUnitOfWorkFactoryPerRequest
    {
        public UnitOfWorkFactory(DBData context)
        {
            Context = context;
        }

        public DBData Context
        {
            get; private set;
        }

        public void Dispose()
        {
            Context.Dispose();
        }
    }

So now if I want to create DBContext per request I will use IUnitOfWorkFactoryPerRequest, and when I want to use DBContext in some background thread I can use IUnitOfWorkFactoryPerCall.

回答1:

My temporary solution. I created singleton which can create Context "in transient way"

public class AppDependencyResolver
{
    private static AppDependencyResolver _resolver;

    public static AppDependencyResolver Current
    {
        get
        {
            if (_resolver == null)
                throw new Exception("AppDependencyResolver not initialized. You should initialize it in Startup class");
            return _resolver;
        }
    }

    public static void Init(IServiceProvider services)
    {
        _resolver = new AppDependencyResolver(services);
    }

    private readonly IServiceProvider _serviceProvider;

    public AppDependencyResolver(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    public IUnitOfWorkFactory CreateUoWinCurrentThread()
    {
        var scopeResolver = _serviceProvider.GetRequiredService<IServiceScopeFactory>().CreateScope();
        return new UnitOfWorkFactory(scopeResolver.ServiceProvider.GetRequiredService<DBData>(), scopeResolver);
    }
}

Then I call init method in Startup Configure method

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    AppDependencyResolver.Init(app.ApplicationServices);
    //other configure code
}

And after all I can call AppDependencyResolver.Current.CreateUoWinCurrentThread() in some background thread.

If someone can provide more elegant solution I will be appreciated.

回答2:

Within your controller, why are you trying to inject into private readonly DBData _context;? If you've registered your IUnitOfWorkFactoryPerCall via DI, you should be injecting that into your controller I believe? You then access your context via the interface.

To expand, this is what I am suggesting you do:

public class HomeController : Controller
{
    private readonly IUnitOfWorkFactoryPerCall _contextFactory;

    public HomeController(IUnitOfWorkFactoryPerCall contextFactory)
    {
        _contextFactory = contextFactory;
    }

    public IActionResult StartInBackground()
    {
        Task.Run(() =>
            {
                Thread.Sleep(3000);
                //System.ObjectDisposedException here
                var res = _contextFactory.Context.Users.FirstOrDefault(x => x.Id == 1);
            });

        return View();
    }
}

来源：https://stackoverflow.com/questions/34952087/ef-7-core-create-dbcontext-like-addtransient