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

Chapter 9: ADO.NET XML Data SerializationOverviewXML is the key element responsible for the greatly improved interoperability of theMicrosoft ADO.NET object model when compared to Microsoft ActiveX Data Objects(ADO). In ADO, XML was merely an I/O format (nondefault) used to persist thecontents of a disconnected recordset. The participation of XML in the building and inthe interworkings of ADO.NET is much deeper. The aspects of ADO.NET in which theinteraction and integration with XML is stronger can be summarized in two categories:object serialization and remoting and a dual programming interface.In ADO.NET, you have several options for saving objects to, and restoring objects from,XML documents. In effect, this capability belongs to one object only—the DataSetobject—but it can be extended to other container objects with minimal coding. Savingobjects like DataTable and DataView to XML is essentially a special case of theDataSet object serialization.As we saw in Chapter 8, ADO.NET and XML classes provide for a unified, intermediateAPI that is made available to programmers through a dual, synchronized programminginterface—the XmlDataDocument class. You can access and update data using eitherthe hierarchical node-based approach of XML or the relational approach of columnbasedtabular data sets. At any time, you can switch from a DataSet representation ofthe data to an XML Document Object Model (XML DOM) representation, and viceversa. Data is synchronized, and any change you enter in either model is immediatelyreflected and visible in the other.In this chapter, we'll explore the XML features built around the DataSet object and otherADO.NET objects for data serialization and deserialization. You'll learn how to persistand restore data contents, how to deal with schema information, and even how schemainformation is automatically inferred from the XML source.Serializing DataSet ObjectsLike any other .NET Framework object, a DataSet object is stored in memory in abinary format. Unlike other objects, however, the DataSet object is always remoted andserialized in a special XML format, called a DiffGram. (We'll look at the DiffGram formatand the relative API in more detail in Chapter 10.) When the DataSet object trespassesacross the boundaries of the application domains (AppDomains), or the physicalborders of the machine, it is automatically rendered as a DiffGram. At its destination,the DataSet object is silently rebuilt as a binary and immediately usable object.In ADO.NET, serialization of an object is performed either through the publicISerializable interface or through public methods that expose the object's internalserialization mechanism. As .NET Framework objects, ADO.NET objects can plug intothe standard .NET Framework serialization mechanism and output their contents tostandard and user-defined formatters. The .NET Framework provides a couple of builtinformatters: the binary formatter and the Simple Object Access Protocol (SOAP)formatter. A .NET Framework object makes itself serializable by implementing themethods of the ISerializable interface—specifically, the GetObjectData method, plus aparticular flavor of the constructor. According to this definition, both the DataSet and theDataTable objects are serializable.In addition to the official serialization interface, the DataSet object supplies analternative, and more direct, series of methods to serialize and deserialize itself, but in aclass-defined XML format only. To serialize using the standard method, you createinstances of the formatter object of choice (binary, SOAP, or whatever) and let the324