08.UsersAndProducts

public static string GetUsersWithProducts(ProductShopContext context)
        {
            var users = context.Users
                .Where(u => u.ProductsSold.Any() && u.ProductsSold.Any(p => p.BuyerId != null))
                .ToArray()
                .Select(u => new UserExportModel
                {
                    FirstName = u.FirstName,
                    LastName = u.LastName,
                    Age = u.Age,
                    SoldProducts = new SoldProductContainer
                    {
                        Count = u.ProductsSold.Count,
                        Products = u.ProductsSold.Select(p => new SoldProductOutputModel
                        {
                            Name = p.Name,
                            Price = p.Price
                        }).OrderByDescending(p => p.Price).ToArray()
                    }
                })
                .OrderByDescending(u => u.SoldProducts.Count)
                .Take(10).ToArray();

            var finalModel = new UserProductsFinalModel
            {
                Count = users.Length,
                Users = users
            };

            var xmlSerializer = new XmlSerializer(typeof(UserProductsFinalModel), new XmlRootAttribute("Users"));

            var namespaces = new XmlSerializerNamespaces();

            namespaces.Add("", "");

            var textWriter = new StringWriter();
            xmlSerializer.Serialize(textWriter, finalModel, namespaces);

            return textWriter.ToString();
        }


[XmlType("User")]
    public class UserExportModel
    {
        [XmlElement("firstName")]
        public string FirstName { get; set; }

        [XmlElement("lastName")]
        public string LastName { get; set; }

        [XmlElement("age")]
        public int? Age { get; set; }

        [XmlElement("SoldProducts")]
        public SoldProductRoot SoldProducts { get; set; }
    }

[XmlType("SoldProducts")]
    public class SoldProductContainer
    {
        [XmlElement("count")]
        public int Count { get; set; }

        [XmlArray("products")]
        public SoldProductOutputModel[] Products { get; set; }

    }

[XmlType("Product")]
    public class SoldProductOutputModel
    {
        [XmlElement("name")]
        public string Name { get; set; }

        [XmlElement("price")]
        public decimal Price { get; set; }
    }

 [XmlRoot("Users")]
    public class UserProductsFinalModel
    {
        [XmlElement("count")]
        public int Count { get; set; }

        [XmlArray("users")]
        public UserExportModel[] Users { get; set; }
    }