Cannot access a disposed object in ASP.NET Core when injecting DbContext

I had a similar issue working with asp.net core. I have an async POST method in my controller and when it returns void I will have this exception. After I changed the POST method return a TASK the problem was solved.

Change from:

public async void PostAsync([FromBody] Model yourmodel)

To

public async Task PostAsync([FromBody] Model yourmodel)

Just a guess in what causes your error:

You are using DI and async calls. If, somewhere in your call stack, you return a void instead of Task, you get the described behavior. At that point, the call is ended and the context disposed. So check if you have an async call that returns a void instead of Task. If you change the return value, the ObjectDisposedException is probably fixed.

public static class DataSeedExtensions {
private static IServiceProvider _provider;

public static async Task SeedData(this IApplicationBuilder builder) { //This line of code

  _provider = builder.ApplicationServices;
  _type = type;

  using (Context context = (Context)_provider.GetService<Context>()) {

    await context.Database.MigrateAsync();
    // Insert data code

  }

}

And in configure:

if (hostingEnvironment.IsDevelopment()){
   await  applicationBuilder.SeedData();
}

Blog post on how to fix this error: Cannot access a disposed object in ASP.NET Core when injecting DbContext

Update for ASP.NET Core 2.1

In ASP.NET Core 2.1 the methods changed slightly. The general method is similar to the 2.0, just the methods name and return types have been changed.

public static void Main(string[] args)
{
    CreateWebHostBuilder(args)
        .Build()
        .Seed();
}

public static IWebHostBuilder CreateWebHostBuilder(string[] args)
{
    return new WebHostBuilder()
        ...; // Do not call .Build() here
}

Applies for ASP.NET Core 2.0

With ASP.NET Core 2.0 there have been some changes in how EF Core tools (dotnet ef migrations etc.) determine the DbContext and connection string at design time.

The below answer leads that the migrations and seeding are applied when calling any of the dotnet ef xxx commands.

The new pattern for getting a design time instance for the EF Core tools is by using an BuildHostWeb static method.

As per this announcement, EF Core will now use the static BuildWebHost method which configures the whole application, but doesn't run it.

  public class Program
  {
      public static void Main(string[] args)
      {
          var host = BuildWebHost(args);

          host.Run();
      }

      // Tools will use this to get application services
      public static IWebHost BuildWebHost(string[] args) =>
          new WebHostBuilder()
              .UseKestrel()
              .UseContentRoot(Directory.GetCurrentDirectory())
              .UseIISIntegration()
              .UseStartup<Startup>()
              .Build();
  }

Replace this in your old Main method

public static void Main(string[] args)
{
    var host = BuildWebHost(args)
        .Seed();

    host.Run();
}

Where Seed is an extension method:

public static IWebHost Seed(this IWebHost webhost)
{
    using (var scope = webhost.Services.GetService<IServiceScopeFactory>().CreateScope())
    {
        // alternatively resolve UserManager instead and pass that if only think you want to seed are the users     
        using (var dbContext = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>()) 
        {
            SeedData.SeedAsync(dbContext).GetAwaiter().GetResult();
        }
    }
}

public static class SeedData
{
    public static async Task SeedAsync(ApplicationDbContext dbContext)
    {
        dbContext.Users.Add(new User { Id = 1, Username = "admin", PasswordHash = ... });
    }
}

Old Answer, still applies to ASP.NET Core 1.x

There is a semi-official pattern on how to seed Entity Framework Core in ASP.NET Core application you should apply, because during application startup there is no Request and hence no RequestServices (which resolves scoped services).

In essence it boils down to creating a new scope, resolve the types you need and dispose the scope again once you're finished.

// serviceProvider is app.ApplicationServices from Configure(IApplicationBuilder app) method
using (var serviceScope = serviceProvider.GetRequiredService<IServiceScopeFactory>().CreateScope())
{
    var db = serviceScope.ServiceProvider.GetService<AppDbContext>();

    if (await db.Database.EnsureCreatedAsync())
    {
        await SeedDatabase(db);
    }
}

One of the reasons directly resolving a service via app.ApplicationServices.GetService<MyService>() is that ApplicationServices is the application (or lifetime) scope provider and the services resolved here stay alive until the application is shut down.

Usually the scoped container will resolve from it's parent container, if the object already exists there. So if you instantiate the DbContext this way in the application, it will be available in ApplicationServices container and when a request happens, a child container will be created.

Now when resolving the DbContext it won't be resolved as scoped, because it already exists in the parent container, so the instance of the parent container will be returned instead. But since it has been disposed during the seeding, it won't be accessible.

A scope container is nothing else then a singleton container with limited lifetime.

So never resolve scoped services in Application startup w/o using the pattern above of first creating a scope and resolving from it.

If you are using any async void please replace it with async Task