Use DbContext in ASP .Net Singleton Injected Class

Question

I need to access my database in a Singleton class instantiated in my Startup class. It seems that injecting it directly results in a DbContext that is disposed.

I get the following error:

Cannot access a disposed object. Object name: 'MyDbContext'.

My question is twofold: Why doesn't this work and how can I access my database in a singleton class instance?

Here is my ConfigureServices method in my Startup class:

public void ConfigureServices(IServiceCollection services) {     // code removed for brevity      services.AddEntityFramework().AddSqlServer().AddDbContext<MyDbContext>(         options =>         {             var config = Configuration["Data:DefaultConnection:ConnectionString"];             options.UseSqlServer(config);         });      // code removed for brevity      services.AddSingleton<FunClass>(); } 

Here is my controller class:

public class TestController : Controller {     private FunClass _fun;      public TestController(FunClass fun)     {         _fun = fun;     }      public List<string> Index()     {         return _fun.GetUsers();     } } 

Here is my FunClass:

public class FunClass {     private MyDbContext db;      public FunClass(MyDbContext ctx) {         db = ctx;     }      public List<string> GetUsers()     {          var lst = db.Users.Select(c=>c.UserName).ToList();         return lst;     } } 

Answer 1

Original source: https://entityframeworkcore.com/knowledge-base/51939451/how-to-use-a-database-context-in-a-singleton-service-

Since DbContext is scoped by default, you need to create scope to access it. It also allows you to handle its lifetime correctly - otherwise you'd keep instance of DbContext for a long time and this is not recommended.

public class Singleton : ISingleton  {      private readonly IServiceScopeFactory scopeFactory;      public Singleton(IServiceScopeFactory scopeFactory)     {         this.scopeFactory = scopeFactory;     }      public void MyMethod()      {         using(var scope = scopeFactory.CreateScope())          {             var db = scope.ServiceProvider.GetRequiredService<DbContext>();              // when we exit the using block,             // the IServiceScope will dispose itself              // and dispose all of the services that it resolved.         }     } }