Using DbContextFactory in a singleton class in Blazor

Question

I'm still trying to wrap my head around how to get a DbContextFactory work with a normal .cs class/singleton.

Here's what I have so far:

program.cs:

var connectionString = builder.Configuration.GetConnectionString("Main");
builder.Services.AddDbContextFactory<MyDBContext>(options => options.UseSqlServer(connectionString));
builder.Services.AddSingleton<MySingletonService>();

MyDBContext.cs:

public class MyDBContext : DbContext
{
    public DbSet<Models.Users> Users { get; set; }
    public DbSet<Models.Orders> Orders { get; set; }
    
    public MyDBContext(DbContextOptions<MyDBContext> options) : base(options)
    {
        _options = options;
    }
}

UsersSingletonService:

public class UsersSingletonService
{
    internal List<Users?> allUsers;

    internal void SetDataUsers(List<Users> value)
        => allUsers = value;
}

UsersScopedService:

public class UsersScopedService
{
    private UsersSingletonService _usersSingletonService;
    //define the DBContextFactory here?
    //private IDbContextFactory<MyDBContext> _dbFactory;
  
    public UsersScopedService(UsersSingletonService usersSingletonService)
    {
        //somehow get the DBContextFactory here?
        //
        _usersSingletonService = usersSingletonService;
    }

     public async ValueTask<List<Users>?> GetUsersDataAsync()
     {
         if (_usersSingletonService.allUsers is null)
         {
             //how do we get DB context here?
             var myDBContext = _dbFactory.CreateDbContext();
             var allUsers = await myDBContext.Users.ToListAsync();
             _usersSingletonService.SetDataUsers(allUsers);
         }
         return _usersSingletonService.allUsers;
     }
}

The idea is to use a singleton to store a "cached" list of Users which I can retrieve with a service class. I know how to inject DbContext into a .razor page but how would I use it with UsersScopedService here?

An additional issue I'm facing is the connection string is in appsettings.json so I don't know how I'd even pass it to DbContext. This code is based on someone suggesting using a DbContextFactory, but I have no idea how to use it.

Can anyone provide any suggestions?

Answer 1

Blazor doesn't offer usable scopes for DI so you will need a using somewhere, the best approach is to have a DbContext-per-method. That only requires a small modification:

//how do we get DB context here?
//var myDBContext = _dbFactory.CreateDbContext();
using var myDBContext = _dbFactory.CreateDbContext();

and then add UsersScopedService as a service and use constructor injection for the dbFactory.