discountsales xmlprocessing excercise

//mapping
  CreateMap<Sale, ExportSaleDto>()
                .ForMember(cfg => cfg.Discount, opt => opt.MapFrom(x => Math.Round(x.Discount,2)))
                .ForMember(cfg => cfg.CustomerName, opt => opt.MapFrom(x => x.Customer.Name))
                .ForMember(cfg=>cfg.ExportFerariCars,opt=>opt.MapFrom(x=>x.Car))
                .ForMember(cfg => cfg.Price,
                    opt => opt.MapFrom(x => Math.Round(x.Car.Parts.Sum(p => p.Part.Price),2)));

//dtos

    [XmlType("sale")]
    public class ExportSaleDto
    {
        [XmlIgnore]
        public decimal Pricewithdiscount;
        [XmlElement("car")]
        public ExportFerariCars ExportFerariCars { get; set; }

        [XmlElement("customer-name")]
        public string CustomerName { get; set; }

        [XmlElement("discount")]
        public double Discount { get; set; }

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

        // i needed to make PriceWithDiscount this way or xmlserializer couldn't see it
        // strange but true and it worked
        [XmlElement("price-with-discount")]
        public decimal PriceWithDiscount
        {
            get => Math.Round(this.Price -= this.Price * (decimal)this.Discount, 2);
            set => Pricewithdiscount = value;
        }
    }
............
   public class ExportFerariCars
    {
        [XmlAttribute("make")]
        public string Make { get; set; }

        [XmlAttribute("model")]
        public string Model { get; set; }

        [XmlAttribute("travelled-distance")]
        public long Distance { get; set; }
    }
//method for the query:
    public static void SalesWithAppliedDiscount(IMapper mapper, CarDealerContext context)
        {
            var sales = context.Sales.ProjectTo<ExportSaleDto>(mapper.ConfigurationProvider).ToArray();

            StringBuilder sb = new StringBuilder();
            var serializer = new XmlSerializer(typeof(ExportSaleDto[]), new XmlRootAttribute("sales"));
            var xmlNameSpaces = new XmlSerializerNamespaces(new[] { XmlQualifiedName.Empty });
            serializer.Serialize(new StringWriter(sb), sales, xmlNameSpaces);
            File.WriteAllText("../../../Xml/sales-discounts.xml", sb.ToString());

        }
//result:
<sales>
  <sale>
    <car make="Ferrari" model="F430" travelled-distance="214647" />
    <customer-name>Marcelle Griego</customer-name>
    <discount>0.05</discount>
    <price>7243.30</price>
    <price-with-discount>6881.14</price-with-discount>
  </sale>
  <sale>
    <car make="Ferrari" model="250 GTO" travelled-distance="213647" />
    <customer-name>Hipolito Lamoreaux</customer-name>
    <discount>0.1</discount>
    <price>6073.98</price>
    <price-with-discount>5466.58</price-with-discount>
  </sale>
  <sale>........