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

Figure 9-6: An application that passes some data to a DataTable object and then persists itto XML.So much for DataTable objects. Let's see what you can do to serialize to XML thecontents of an in-memory, possibly filtered, view.Inside the DataView ObjectThe DataView class represents a customized view of a DataTable object. Therelationship between DataTable and DataView objects is governed by the rules of awell-known design pattern: the document/view model. According to this model, theDataTable object acts as the document, and the DataView object acts as the view. Atany moment, you can have multiple, different views of the same underlying data. Moreimportant, you can manage each view as an independent object with its own set ofproperties, methods, and events.The view is implemented by maintaining a separate array with the indexes of theoriginal rows that match the criteria set on the view. By default, the table view isunfiltered and contains all the records included in the table. By configuring theRowFilter and RowStateFilter properties, you can narrow the set of rows that fit into aparticular view. Using the Sort property, you can apply a sort expression to the rows inthe view. Figure 9-7 illustrates the internal architecture of the DataView object.Figure 9-7: A DataView object maintains an index of the table rows that match the criteria.When any of the filter properties is set, the DataView object gets from the underlyingDataTable object an updated index of the rows that match the criteria. The index is asimple array of positions. No row objects are physically copied or referenced at thistime.340