ObjectDisposedException on a ASP.NET Core 2.0 MVC custom database initializer class

I'm getting the following exception in my custom database initializer class:

System.ObjectDisposedException occurred HResult=0x80131622
Message=Cannot access a disposed object. A common cause of this error is disposing a context that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling Dispose() on the context, or wrapping the context in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances. Source= StackTrace: at Microsoft.EntityFrameworkCore.DbContext.CheckDisposed() at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider() at Microsoft.EntityFrameworkCore.DbContext.get_DbContextDependencies() at Microsoft.EntityFrameworkCore.DbContext.d__48.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.AspNetCore.Identity.EntityFrameworkCore.UserStore9.<CreateAsync>d__22.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter1.GetResult() at Microsoft.AspNetCore.Identity.UserManager1.<CreateAsync>d__73.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter1.GetResult() at Microsoft.AspNetCore.Identity.UserManager1.<CreateAsync>d__78.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter1.GetResult() at LlabApp.Data.DbInitializer.d__4.MoveNext() in E:\C# projects\Atenea\LlabApp\LlabApp\LlabApp\Data\DbInitializer.cs:line 58

Here is the Initializer:

public class DbInitializer : IDbInitializer
{
    private readonly ApplicationDbContext _Context;
    private readonly UserManager<ApplicationUser> _userManager;
    private readonly RoleManager<ApplicationRole> _roleManager;

    public DbInitializer(
        ApplicationDbContext context,
        UserManager<ApplicationUser> userManager,
        RoleManager<ApplicationRole> roleManager)
    {
        _context = context;
        _userManager = userManager;
        _roleManager = roleManager;
    }

    public async void Initialize()
    {
        var adminUsers = _userManager.GetUsersInRoleAsync(RoleClaimValues.Admin).Result;
        if (adminUsers == null || adminUsers.Count == 0)
        {
(...)
        }
     }
}

public interface IDbInitializer
{
    void Initialize();
}

And here is the startup.cs where i add the scope of IDbInitializer in ConfigureService and then call it from Configure:

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }


    public void ConfigureServices(IServiceCollection services)
    {
        // Add framework services.
        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("ApplicationConnection")));

        services.AddIdentity<ApplicationUser, ApplicationRole>(o => {
            o.Password.RequireDigit = false;
            o.Password.RequiredLength = 4;
            o.Password.RequireLowercase = false;
            o.Password.RequireUppercase = false;
            o.Password.RequireNonAlphanumeric = false;
            o.User.RequireUniqueEmail = true;
        })
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();

        services.AddMvc();

        // Add application services.
        services.AddTransient<IEmailSender, MessageServices>();
        //Seed database
        services.AddScoped<IDbInitializer, DbInitializer>();
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IDbInitializer dbInitializer)
    {
        loggerFactory.AddConsole();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();

            app.UseBrowserLink();
            app.UseDatabaseErrorPage();

            app.UseStatusCodePages("text/plain", "Status code page, status code: {0}");
        }
        else
        {
            app.UseExceptionHandler("/Error");
        }

        app.UseStaticFiles();
        app.UseAuthentication();

        dbInitializer.Initialize();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

I don't know why the exception tells that the problem could be that the context is disposed somewhere.

I've also added

.UseDefaultServiceProvider(options =>
  options.ValidateScopes = false)

after .UseStartup<Startup>() just in case it was something relative to the scopes, but the exception is the same.

I had the same problem as you had. You indeed have to change all code to return a Task. Otherwise the DbContext is disposed before all actions are done.

Database Initialization is changed in dotnet core 2.0. I created a blog about this specific topic. See http://www.locktar.nl/programming/net-core/seed-database-users-roles-dotnet-core-2-0-ef/ for more information.