Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

Writing an XSLT style sheet to transform a DataSet object into a Recordset object isuseful for other reasons as well. First, the style sheet code needed is not trivial andrequires a good working knowledge of both XPath and XSLT. Look at it as a usefulexercise to test your level of familiarity with the technologies. Second, you can applythe style sheet directly to the binary DataSet object, without first serializing the object toXML.The ability to style a binary DataSet object is provided by the XmlDataDocument class.As mentioned in Chapter 6, XmlDataDocument is an XPath document class. Itimplements the IXPathNavigable interface and, as such, can be directly passed as anargument to the Transform method. (We'll examine the XmlDataDocument class indetail in Chapter 8.)Getting the DataSet ObjectThe following code fetches some records from the Northwind database's Employeestable and stores them into a DataSet object:string conn = "DATABASE=northwind;SERVER=localhost;UID=sa;";string comm = "SELECT firstname, lastname, title, notes FROMemployees";SqlDataAdapter adapter = new SqlDataAdapter(comm, conn);DataSet data = new DataSet("Northwind");adapter.Fill(data, "Employees");The DataSet object is named Northwind and contains just one DataTable object,Employees. As we'll see in a moment, the names of the DataSet and DataTable objectsplay a key role in the XML representation of the objects. By default, a DataSet object isnamed NewDataSet, and a DataTable object is named Table. (We'll look at ADO.NETXML serialization in great detail in Chapter 9 and Chapter 10.)The XML representation of a DataSet object looks like this:......⋮⋮TipYou can get the string representing the XML version of the DataSetobject through the DataSet method GetXml. The text does not includeschema information. You can get the schema script separately bycalling the GetXmlSchema method. To persist the XMLrepresentation to a stream, use the WriteXml method instead.Transforming the DataSet ObjectTransforming a DataSet object into a Recordset object poses a couple of problems.The first is that you have to infer and write the Recordset object's schema. The secondis that the XML layout of the DataSet object depends on a number of differentparameters. In particular, the root of the XML version of the DataSet object depends on267