Get transistent/scoped Database access in singletonservice - asp.net

Question

i updating my app from asp core 1.0 to 2.0. In 1.0 i have a soulution for my longlive import-task, initialated as singleton. The singleton used the DBContext. But in core 2.0 this soulution dosn't work. Can you help me?
My soulution in aps core 1.0 was
services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("LocalConnection")));
services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
services.AddTransient<IDataStore, DataStore>();
services.AddSingleton<IImportRepository, ImportRepository>();
with
public class ImportRepository : IImportRepository
{
Importer Importer;
private readonly ApplicationDbContext DBContext;
private readonly IDataStore store;
private ImportSet runningSet = null;
public ImportRepository(ApplicationDbContext context, IDataStore store)
{
this.DBContext = context;
this.store = store;
Importer = new Importer(DBContext, store);
}
With this soulutions i get errormessages (in german, but i try to translate). "you cannot use scoped services in singleton"
Last attempt i used this solution
services.AddSingleton<ImportService>(
provider => new ImportService((ApplicationDbContext)provider.GetService(typeof(ApplicationDbContext)))
);
But here i get the errormessage "Cannot resolve scoped service 'Portal.Data.ApplicationDbContext' from root provider."
How can i get access to my database in my Import-Service?

Answer 1

You may resolve dependencies manually using IServiceProvider instance.
public class ImportRepository : IImportRepository
{
private readonly IServiceProvider _provider;
public ImportRepository(IServiceProvider provider)
{
_provider = provider;
...
}
public void DoSomething()
{
var dBContext = (ApplicationDbContext) provider.GetService(typeof(ApplicationDbContext));
...
}
}
By the way, there is an extension method GetService<T>(); defined in Microsoft.Extensions.DependencyInjection namespace:
// using Microsoft.Extensions.DependencyInjection;
var dBContext = provider.GetService<ApplicationDbContext>();

Answer 2

Since your singleton lives longer and is shared, the only option I see is that you take it as a parameter to the functions.
public class ImportRepository : IImportRepository
{
public void DoSomething(ApplicationDbContext context, IDataStore store)
{
}
}
The other option is to make ImportRepository scoped as well.

Answer 3

Ok. I have a soulution, that works, but not perfektly.
Like Juunas example i build a long life funktion
public async Task RunImportAsync(string fileName, DataService data)
{
await Task.Run(() =>
{
if (!System.IO.File.Exists(internalPath + fileName))
{
throw new Exception($"Datei {fileName} nicht gefunden.");
}
[long Operations...]
data.DBContext.Add(new ImportHistory(set));
data.DBContext.SaveChanges();
});
}
the call is simple
[HttpPost]
[Route("runImport")]
public async Task<IActionResult> RunImport([FromBody]dynamic body)
{
string id = "";
try
{
id = body.filename;
_logger.LogInformation($"Import from {id}");
await ImportService.RunImportAsync(id, DB);
return StatusCode(StatusCodes.Success_2xx.OK);
}
catch (Exception e)
{
return SendError(e);
}
}
But postmen get no Response with this solution. Is there a idea, how i can fix it?