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

The XML reader will loop through the nodes, moving from one record to the next, asshown here:void ProcessNotes(XmlTextReader reader){try{while(reader.Read()){if (reader.NodeType == XmlNodeType.Text)MessageBox.Show(reader.Value);}}catch {}finally{MessageBox.Show("Closed...");}}The connection remains open until the reader is closed. Next store the results in astring variable and use that string to create a new XmlTextReader object. (See Chapter2.) This technique gives you an extra advantage: you can work with the reader whileyou are disconnected from the database.An XML Reader for Data ReadersAn XML reader can work on top of different data containers, including streams, files,and text readers. By writing a custom XML reader, you can also navigate non-XML datausing the same XML reader metaphor. In this case, you create a virtual XML tree andmake the underlying data look like XML. (In Chapter 2, you learned how to visit CSVfiles the XML way.)The ability to expose result sets via XML is specific to SQL Server 2000 and potentiallyto any other native managed provider for DBMS systems with full support for XMLqueries. You can't, for example, use the ExecuteXmlReader method with an object ofclass OleDbCommand.Recall from the section "Under the Hood of ExecuteXmlReader," on page 366, theinternal structure of ExecuteXmlReader. The ExecuteXmlReader method simplycreates an XML text reader based on the internal stream used to carry data back andforth. What about creating a custom XML reader by building a virtual XML tree aroundthe provider-specific data reader? In this way, you could easily extend any .NETFramework data provider by using the ExecuteXmlReader method. This method is notas effective as using the internal stream, but it does work and can be applied to all dataproviders.Building the XML Data ReaderLet's rework the CSV reader example from Chapter 2 and build an XmlDataReaderclass inheriting from XmlReader, as follows:public class XmlDataReader : XmlReader{299