Entity Framework + Sqlite

            await Task.Run(() =>
           {
               api = new DataContext();
               customers = new ObservableCollection<Customer>((from p in api.Customers
                                                               where p.isBanned == null || p.isBanned == false
                                                               select p).ToList());
               OnPropertyChanged(nameof(Customers));
           });

          api = new DataContext();
           orders = new ObservableCollection<Order>((from p in api.Orders select p).ToList());
           OnPropertyChanged(nameof(Orders));
 
           using(var data = new DataContext()) 
           {
                   data.Managers.Load();
                   data.Products.Load();
                   data.Customers.Load();
                   Products = new ObservableCollection<Product>(data.Products.Local.ToList());
                   Customers = new ObservableCollection<Customer>(data.Customers.Local.ToList());
                   Managers = new ObservableCollection<Manager>(data.Managers.Local.ToBindingList());
           }

public class Order : ...
{
      ...
         private Customer customer;
        public virtual Customer Customer { get => customer; set { Set(ref customer, value); CustomerID = value.CustomerID; } }
 
        private Manager manager;
        public virtual Manager Manager { get => manager; set { Set(ref manager, value); ManagerID = value.ManagerID; } 
}