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

Linking Tables and ViewsThe link between the DataTable object and the DataView object is typically establishedat creation time through the constructor, as shown here:public DataView(DataTable table);However, you could also create a new view and associate it with a table at a later timeusing the DataView object's Table property, as in the following example:DataView dv = new DataView();dv.Table = dataSet.Tables["Employees"];You can also obtain a DataView object from any table. In fact, the DefaultView propertyof a DataTable object simply returns a DataView object initialized to work on that table,as shown here:DataView dv = dt.DefaultView;Originally, the view is unfiltered, and the index array contains as many elements asthere are rows in the table.Getting Views of RowsThe contents of a DataView object can be scrolled through a variety of programminginterfaces, including collections, lists, and enumerators. The GetEnumerator method inparticular ensures that you can walk your way through the records in the view using thefamiliar foreach statement.The following code shows how to access all the rows that fit into the view:DataView myView = new DataView(table);foreach(DataRowView rowview in myView){// Dereferences the DataRow objectDataRow row = rowview.Row;}⋮When client applications access a particular row in the view, the class expects to find itin an internal rows cache. If the rows cache is not empty, the specified row is returnedto the caller via an intermediate DataRowView object. The DataRowView object is awrapper for the DataRow object that contains the actual data. You access row datathrough the Row property. If the rows cache is empty, the DataView class fills it with anarray of DataRowView objects, each of which references an original DataRow object.The rows cache can be empty either because it has not yet been used or because thesort expression or the filter string has been changed in the meantime.Serializing DataView ObjectsThe AdoNetXmlSerializer class also provides overloaded methods to serialize aDataView object. You build a copy of the original DataTable object with all the rows(and only those rows) that match the view, as shown here:public staticvoid WriteDataView(DataView dv, string outputFile, XmlWriteModemode)341