.NET & XML

Synchronizing Data

Take a look at the following code snippet:

AngusHardware dataSet = new AngusHardware( );

XmlDataDocument doc = new XmlDataDocument(dataSet);
doc.Load("HierarchicalCoupons.xml");

XmlTextWriter writer = new XmlTextWriter(Console.Out);
writer.Formatting = Formatting.Indented;

dataSet.WriteXml(writer);

You’ve already seen code that uses this pattern It creates an instance of a DataSet, specifically the one we generated for the Angus Hardware coupon database. Then it loads the DataSet with data from an XML file by creating an XmlDataDocument for it. When the data is written to the console, it appears in a relational XML format.

But if you change the last line, as shown below, you get hierarchical XML output that matches the format and content of the document you loaded into the XmlDataDocument:

doc.WriteTo(writer);

The XmlDataDocument knows how to map between the relational form of the DataSet and the hierarchical form of the document it’s been loaded with, as long as the element names are the same. In fact, it handily ignores any elements it’s not familiar with from the schema in the DataSet when it writes the relational XML.

This is handy because you can read in XML from the hierarchical format and edit it using the DataSet, then output it back into the hierarchical XML. In other words, you can accomplish all the work this lengthy bit of DOM code does:

dataSet.EnforceConstraints = false; XmlElement coupons = doc.CreateElement("coupons"); doc.DocumentElement.AppendChild(coupons); ...