.NET Core 6 inject databasecontext to Singleton Service

Question

I have a problem when try to use database context in one Singleton Service in my app.

App.cs

...
var service = builder.Services;
service.AddDbContext<MyDBContext>(options => options.UseSqlite(connectionString));
service.AddSingleton<MyMonitorManager>();
...

MyDBContext.cs

public class MyDBContext : ApiAuthorizationDbContext<ApplicationUser>
  {
    public DroneDBContext(...): base(options, operationalStoreOptions){}
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder){}
    protected override void OnModelCreating(ModelBuilder modelBuilder){}
  }

MyMonitorManager.cs

public class MyMonitorManager {
   private readonly MyDBContext _databaseManager;
   ...
}

There are errors:

Cannot consume scoped service 'MyController.MyDBContext' from singleton 'MyController.Service.MyMonitorManager'.

I try to search here and think about use like this:

MyDBContext dbContext = new MyDBContext();
service.AddSingleton(new MyMonitorManager(dbContext));

But not sure this is how I should do in .NET 6

Check this link https://stackoverflow.com/questions/45810851/cannot-consume-scoped-service-imongodbcontext-from-singleton-iactiveusersservice — Ertugrul Sungur, Sep 06 '22 at 08:30
This is explained in [Use scoped services within a BackgroundService](https://learn.microsoft.com/en-us/dotnet/core/extensions/scoped-service) — Panagiotis Kanavos, Sep 06 '22 at 08:40

score 4 · Accepted Answer · answered Sep 06 '22 at 08:32

You can use IServiceScopeFactory in your singleton class to create a new scope, and then get a db context reference from that:

public class MyMonitorManager {
    private readonly IServiceScopeFactory _scopeFactory;
 
     public MyMonitorManager(IServiceScopeFactory _scopeFactory)
     {
        _scopeFactory = scopeFactory;
     }
 
     public SomeMethod()
     {
        using (var scope = _scopeFactory.CreateScope())
        {
            var db = scope.ServiceProvider.GetRequiredService<MyDBContext>();
            ...
        }
     }
}

note: if `context` does not exist, `GetRequiredService` throw exception, but `GetService` return `null` — Okan Karadag, Sep 06 '22 at 10:52

Guru Stron · Answer 2 · 2022-09-06T08:46:27.697

You can't inject directly scoped service into singleton, you have follwoing options:

Register database context with different lifetime, though in general case it is not the best option:

service.AddDbContext<MyDBContext>(options => options.UseSqlite(connectionString), ServiceLifetime.Transient);

Inject IServiceScopeFactory to create scope and resolve context when needed the singleton service:

public class MyMonitorManager 
{
   private readonly IServiceScopeFactory _scopeFactory; 
   public class MyMonitorManager(IServiceScopeFactory scopeFactory) => _scopeFactory = scopeFactory;

    public void SomeMethod()
    {
        using (var scope = _serviceScopeFactory.CreateScope())
        {
            var ctx = scope.ServiceProvider.GetService<MyDBContext>(); 
            // use context
        }
    }
}

.NET Core 6 inject databasecontext to Singleton Service

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