// az otgore sum si naprail static settings da ne gi povtarqm v vseki method zatova gi nqma dolu :D

public static string GetSoldProducts(ProductShopContext context)
        {
            var users = context.Users
                .Where(u => u.ProductsSold.Count >= 1 && u.ProductsSold.Any(p => p.Buyer != null))
                .Select(u => new
                {
                    u.FirstName,
                    u.LastName,
                    SoldProducts = u.ProductsSold
                                        .Select(pd => new
                                        {
                                            pd.Name,
                                            pd.Price,
                                            BuyerFirstName = pd.Buyer.FirstName,
                                            BuyerLastName = pd.Buyer.LastName
                                        })
                                        .ToList()
                })
                .OrderBy(u => u.LastName).ThenBy(u => u.FirstName)
                .ToList();

            var json = JsonConvert.SerializeObject(users, settings);

            return json;
        }