Cannot consume scoped service 'MyDbContext' from singleton 'Microsoft.AspNetCore.Hosting.Internal.HostedServiceExecutor'

Question

I\'ve build a background task in my ASP.NET Core 2.1 following this tutorial: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-

Answer 1

Though @peace answer worked for him, if you do have a DBContext in your IHostedService you need to use a IServiceScopeFactory.

To see an amazing example of how to do this check out this answer How should I inject a DbContext instance into an IHostedService?.

If you would like to read more about it from a blog, check this out .

Answer 2

You still need to register MyDbContext with the service provider. Usually this is done like so:

services.AddDbContext<MyDbContext>(options => {
    // Your options here, usually:
    options.UseSqlServer("YourConnectionStringHere");
});

If you also posted your Program.cs and Startup.cs files, it may shed some more light on things, as I was able to quickly setup a test project implementing the code and was unable to reproduce your issue.

Answer 3

You need to inject IServiceScopeFactory to generate a scope. Otherwise you are not able to resolve scoped services in a singleton.

using (var scope = serviceScopeFactory.CreateScope())
{
  var context = scope.ServiceProvider.GetService<MyDbContext>();
}

Edit: It's perfectly fine to just inject IServiceProvider and do the following:

using (var scope = serviceProvider.CreateScope()) // this will use `IServiceScopeFactory` internally
{
  var context = scope.ServiceProvider.GetService<MyDbContext>();
}

The second way internally just resolves IServiceProviderScopeFactory and basically does the very same thing.

Answer 4

I found the reason of an error. It was the CoordinatesHelper class, which is used in the the background task OnlineTaggerMS and is a Transient - so it resulted with an error. I have no idea why compilator kept throwing errors pointing at MyDbContext, keeping me off track for few hours.