Read large XML file in .NET (C#)

This article shows how you can read nested and complex large XML file using XmlReader.

few benefits of using XmlReader

• XmlReader reads data in a forward-only and read-only fashion. That’s why it is faster than loading XML in memory and read node by node.
• XmlReader reads line by line.
• You can use ReadState property to check the current state of the reader.
• You can define XMLReaderSettings to customize reader behavior. (see below example)

Sample Xml

<?xml version="1.0" encoding="UTF-8"?>
<cafProductFeed>
<datafeed id="7858" merchantId="7858" merchantName="SampleMerchant">
<prod id="672553505" in_stock="yes" is_for_sale="yes" pre_order="no" stock_quantity="2" web_offer="no">
	<brand/>
	<cat>
		<mCat>B2C_2</mCat>
	</cat>
	<price curr="GBP">
		<buynow>33.99</buynow>
		<rrp>0.00</rrp>
		<store>0.00</store>
	</price>
	<text>
		<name>Laptop Memory</name>
	</text>
	<uri>
		<track>link</track>
		<mImage>link</mImage>
		<mLink>link</mLink>
	</uri>
	<vertical/>
	<pId>387912</pId>
	<delTime>Free Delivery</delTime>
	<lastUpdated>2020-11-02 09:58:02</lastUpdated>
	<mpn>KVR16S11/8</mpn>
</prod>
//more prod nodes
</datafeed>
</cafProductFeed>

Steps ..

• Define XMLReaderSettings (optional)
• Create XMLReader (XmlReader.Create)
• Read Reader (reader.Read())

Read attributes

As I have discussed before reader read line by line. When the reader reading any node you can get its attributes by following the command. Such as

reader.GetAttribute("in_stock")

Read Sub nodes

if (reader.Name == "pId")
{
    product.MerchantProdId = reader.ReadInnerXml();
}

Example code

        public static List<Product> Products(string filePath)
        {
            XmlReaderSettings settings = new XmlReaderSettings();
            settings.DtdProcessing = DtdProcessing.Parse;
            settings.IgnoreWhitespace = true;
            var results = new List<Product>();
            var product = new Product();
            var merchantName = string.Empty;
            int merchantId = 0;
            long ean = 0;
            long upc = 0;
            long mpn = 0;
            using (XmlReader reader = XmlReader.Create(filePath, settings))
            {
                while (reader.Read())
                {
                    if (reader.NodeType == XmlNodeType.Element)
                    {
                        if (reader.Name == "prod")
                        {
                            if (product.SupplierProdId > 0 && (!string.IsNullOrEmpty(product.Mpn) || !string.IsNullOrEmpty(product.Ean) || !string.IsNullOrEmpty(product.Upc)))
                                results.Add(product);
                            long id;
                            long.TryParse(reader.GetAttribute("id"), out id);
                            int stock;
                            int.TryParse(reader.GetAttribute("stock_quantity"), out stock);
                            product = new Product
                            {
                                SupplierProdId = id,
                                InStock = reader.GetAttribute("in_stock") == "yes",
                                IsForSale = reader.GetAttribute("is_for_sale") == "yes",
                                PreOrder = reader.GetAttribute("pre_order") == "yes",
                                WebOffer = reader.GetAttribute("web_offer") == "yes",
                                StockQuantity = stock
                            };
                        }
                        if (reader.Name == "pId")
                        {
                            product.MerchantProdId = reader.ReadInnerXml();
                        }
                        if (reader.Name == "mpn")
                        {
                            var strMpn = reader.ReadInnerXml();
                            long.TryParse(strMpn, out mpn);
                            if (mpn > 0)
                            {
                                product.Ean = strMpn;
                            }
                            else
                            {
                                product.Mpn = strMpn;
                            }
                        }
                        if (reader.Name == "ean")
                        {
                            var strEan = reader.ReadInnerXml();
                            long.TryParse(strEan, out ean);
                            if (ean <= 0)
                                product.Mpn = strEan;
                            else
                                product.Ean = strEan;
                        }
                        if (reader.Name == "upc")
                        {
                            var strUpc = reader.ReadInnerXml();
                            long.TryParse(strUpc, out upc);
                            if (upc <= 0)
                                product.Mpn = strUpc;
                            else
                                product.Upc = strUpc;
                        }
                        if (reader.Name == "track")
                        {
                            product.Url = reader.ReadInnerXml();
                        }
                        if (reader.Name == "name")
                        {
                            product.Name = reader.ReadInnerXml();
                        }
                        if (reader.Name == "datafeed")
                        {
                            int.TryParse(reader.GetAttribute("merchantId"), out merchantId);
                            merchantName = reader.GetAttribute("merchantName");
                        }
                        if (reader.Name == "price")
                        {
                            product.Currency = reader.GetAttribute("curr");
                        }
                        if (reader.Name == "buynow")
                        {
                            product.Price = Convert.ToDouble(reader.ReadInnerXml());
                        }
                        if (reader.Name == "rrp")
                        {
                            product.RetailPrice = Convert.ToDouble(reader.ReadInnerXml());
                        }
                        if (reader.Name == "store")
                        {
                            product.StorePrice = Convert.ToDouble(reader.ReadInnerXml());
                        }
                        product.MerchantId = merchantId;
                        product.MerchantName = merchantName;
                    }
                }
            }
            return results;
        }