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The SqlXmlAdapter ClassThe SqlXmlAdapter class is a shrink-wrapped adapter class. It does not implement theIDataAdapter interface, so technically speaking, it can't be presented as an adapterobject. Nevertheless, the class provides adapter-like methods such as Fill and Update,as shown in the following code. These are also the only public methods for the class.void Fill(DataSet ds);void Update(DataSet ds);The SqlXmlAdapter class also provides three constructors, shown in the following code,whose signatures reinforce the idea that this adapter is a mere wrapper class forSqlXmlCommand. In other words, the SqlXmlAdapter class is more a command thatmanages DataSet objects than a true data adapter object as it is described in theADO.NET specification.public SqlXmlAdapter(SqlXmlCommand cmd)public SqlXmlAdapter(string commandText,SqlXmlCommandType cmdType,string connectionString)public SqlXmlAdapter(Stream commandStream,SqlXmlCommandType cmdType,string connectionString)These constructors use the information they receive to set up an internal instance of theSqlXmlCommand class. The Fill method makes full use of all the information passedthrough the constructor. For the Update method, on the other hand, only the connectionstring information is actually needed.Filling an XML AdapterThe Fill method is rather simple. First it executes the embedded XML command usingExecuteStream. Next it uses the returned memory stream to fill the specified DataSetobject through its ReadXml method.The ReadXml method populates a DataSet object by reading XML data from a varietyof sources, including streams and text readers, and inferring the schema. We'll examinethe inference process in detail in Chapter 9. For now, suffice to say that ReadXml candetect any in-line or referenced XSD schema or determine the schema dynamically.Once the DataSet object has been filled from the XML stream generated by thecommand execution, all the changes are accepted so that the DataSet object appearsintact and with no pending changes.Updating Using an XML AdapterThe Update method takes a DataSet object and applies its pending changes to thetarget database. The parameters specified on instantiation contain the details about theconnection string. The embedded SqlXmlCommand object has command text and acommand type that are simply ignored during Update. Let's see why.When Update executes, the embedded command object is used to perform the task,but its command text and command type properties are silently and temporarilyoverwritten with DataSet-specific settings.The Update method writes the contents of the DataSet object to a newly createdmemory stream. The DataSet object is serialized as a DiffGram. Next the contents ofthe stream—that is, the DiffGram representation of the DataSet object—are copied intothe CommandText property of the underlying SqlXmlCommand object. TheCommandType property is set to Template, and ExecuteStream is called to update the321
database. If all goes well, the DataSet changes are committed using the DataSetobject's AcceptChanges method.Although COM is still involved, the SqlXmlAdapter object represents a way toarchitecturally improve the batch update mechanism in ADO.NET. By usingSqlXmlAdapter, you actually obtain a DataSet object that is serialized as a DiffGramdirectly to SQL Server and processed entirely on the server. To optimize the bandwidth,you can pass a DataSet object that contains only changed rows. The GetChangesmethod provides for that.NoteUsing GetChanges with ADO.NET batch updating is not asignificant optimization—it simply reduces the total number ofiterations, but the eliminated iterations are no-op by design. Instead,using GetChanges with SqlXmlAdapter can be a key optimization,as it truly minimizes the amount of data being transferred from theclient to SQL Server.ConclusionIn this chapter, we have explored the connections between databases (SQL Server2000 in particular) and XML. Several DBMS systems provide XML support in variousforms. The industry standard, however, requires that a DBMS provide for direct XMLresult sets and accept changes expressed as XML streams. SQL Server 2000 adheresto these requirements.The difficulty lies in .NET and the different connecting model it introduces—.NETFramework data providers instead of OLE DB providers. For .NET Frameworkapplications, fetching data as XML is much easier and more effective than persistingchanges as XML. For COM applications, the same features are more balanced. Thereason is that SQL Server 2000 came out much earlier than the .NET Framework, butthe .NET Framework still came too soon to allow the managed provider to be designedwith a broader perspective.As a result, the SQL Server managed provider is unaware of XML extensions tosupport FOR XML queries and their limitations. Incidentally, this feature, combined withthe power of .NET Framework XML readers, produces a really powerful toolkit. Thetruth, however, is that today the SQL Server managed provider is designed andoptimized for traditional SQL commands—period.SQLXML 3.0 is an add-on conceived to extend the SQL Server 2000 support for XML.SQLXML 3.0 is just that, however; in no way does it represent an integration to the.NET Framework managed provider model. For this reason, it is entirely based on COMOLE DB providers. The managed classes are wrappers around the SQLXMLOLEDBprovider and, as such, require your code to silently jump out of the CLR duringexecution. This does not mean that you should not use SQLXML 3.0—just be aware ofthe managed classes' understandable, but still not optimal, design.Hopes for the future? That's easy—my wish is that SQLXML 3.0 will be improved andintegrated with the .NET Framework managed provider. As a side effect of thisintegration, ADO.NET should be enriched with a kind of Updategram object specificallydesigned for server-side batch updates.In Chapter 9, we'll tackle DataSet serialization and the theme of XML serialization forkey ADO.NET objects in general, including DataTable and DataView objects. We'll alsotake another look at DiffGrams. DiffGrams will be explored in depth in Chapter 10.322
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Applied XML Programming for Microso
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services. Rainer Heller of Siemens
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IntroductionIt was about five years
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What Do I Need to Use This Book?Mos
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Part I: XML Core Classes in the .NE
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Related XML StandardsTable 1-1 list
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XMLDOM model (memory footprint and
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⋮A configuration section handler
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managed application, you must first
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Figure 1-1: Streams can be read and
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abstraction and explicitly indicate
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The XPath Query EngineXPath is a la
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Chapter 2: XML ReadersIn the Micros
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Table 2-1: Public Properties of the
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Table 2-3: Public Methods of the Xm
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Table 2-4: Types of Nodes in the Xm
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To produce these results, I created
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In particular, the XmlConvert class
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The method we create to do this is
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Consider the following attribute va
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An entity reference consists of the
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The NameTable ObjectOne of the secr
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End ClassByVal type As XmlNodeType)
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Fragments and Parser ContextThe con
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You can specify other settings for
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FullerAndrewSales ManagerLeverlingJ
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String[] m_headerValues;tokensbool
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get{if(m_readState != ReadState.Int
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}public override string this[string
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}}return false;The name of the attr
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dt.Columns.Add(col);}reader.MoveToE
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Readers and XML ReadersTo cap off o
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Chapter 3: XML Data ValidationOverv
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The XmlValidatingReader Programming
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The ValidationEventHandler EventThe
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Figure 3-1: The sample application
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document, no event is fired, but an
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valtype = "Auto.XDR";Figure 3-2 sho
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validator object for further proces
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);This method creates and adds a ne
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public XmlValidatingReader(Stream,
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XML InteroperabilityAs you can see,
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XSDs are more powerful than DTDs, a
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Compared to the DTD schema, this XD
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xmlns:z='#RowsetSchema'>This simple
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Figure 3-7: The XSD type hierarchy.
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Table 3-6: Mapping Between XSD and
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Table 3-7: Top-Level Elements for X
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The next step is to define a new sc
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Creating an XML Schema with Visual
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Figure 3-10: The graphical represen
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Open the XML readerXmlTextReader re
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Define the pattern for the contentX
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ody of the element. It is a simple
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determine the correct sequence and
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The root element can't be successfu
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Francesco Balena's Programming Visu
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}sw.Write(sb.ToString());sw.Close()
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What the XmlWriter Class Can't DoAl
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stream. Some working memory is free
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Table 4-5: Miscellaneous Writing Me
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If you want to get just the default
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else you might need that the writer
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By using the pubid argument (PUBLIC
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Figure 4-3: A dynamically created X
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This command executes normally, but
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"dinoe:isbn-0735618011");This code
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writer.WriteStartElement("element")
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}writer.WriteEndDocument();writer.C
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}}reader.Close();If in this code yo
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Figure 4-8: A PictureBox control di
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NoteThe entire source code for a sa
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Table 4-8: Public Methods of the Xm
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}Writer.WriteStartElement("xml");Wr
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Testing the XmlRecordsetWriter Clas
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Framework type and map each to an e
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}if (i % 2)writer.WriteNode(reader,
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Table 4-9: Methods of the XmlTextRe
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while(rw.Read()){switch(rw.NodeType
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if (m_reader.HasAttributes){// Cons
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Figure 4-14: The code can be used t
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}}rw.Writer.WriteStartElement(rw.Re
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Note The new keyword is C#-specific
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}The net effect of this code is tha
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.NET XML writers only ensure the we
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Part II: XML Data ManipulationChapt
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3JanetLeverlingWhen processed by an
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child elements when processing an X
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through the base class XmlNode. (Se
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Table 5-3: Events of the XmlDocumen
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Both XmlLinkedNode and XmlCharacter
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Figure 5-3: The XmlLinkedNode class
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Working with XML DocumentsTo be ful
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}}{if (n.NodeType == XmlNodeType.El
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While the secondary thread works, t
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Limitations of the XML DOM Eventing
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XML document is often overkill unle
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If you use a namespace, you might r
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Extending the XML DOMAlthough the .
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Table 5-6: Programming Interface of
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file changes, irrespective of the c
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Figure 5-7: The sample application
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Chapter 6: XML Query Language and N
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Figure 6-1: A sample XML tree in wh
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with the forward slash (/). The fol
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How XPointer Uses XPathAn XPointer
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the caller. Using SelectSingleNode
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StringBuilder sb = new StringBuilde
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Figure 6-4: The node set returned b
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A Better Way to Select a Single Nod
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3. Optionally, precompile the XPath
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Table 6-3: Properties of the XPathN
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the type. In addition, attributes a
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As you can see, several methods hav
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Setting Namespace InformationThe in
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string strX = (string) x;string str
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the navigator's author must careful
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⋮Notice that the sample file syst
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Table 6-10: Properties of the XPath
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supplies the underlying means to id
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• XSL Formatting Objects (XSL-FO)
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HTML," on page 299. In the meantime
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Table 7-2: XSLT Instructions for Da
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Table 7-4: XSLT Instructions for La
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In the first template, the context
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……⋮The expected target schema
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By the way, note that the version a
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The XslTransform ClassNow that we'v
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To avoid threading risks, be aware
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index of the style sheet contents.
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Table 7-7: Transform Method Overloa
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XSLT Output RecordsThe output of th
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Perform the transformation, record
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method, other attributes of interes
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Table 7-8: Methods of the XsltArgum
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the object's DataSetName property.
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The diffgr:error attribute on the r
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{}// Url is a form property that po
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...By design, the current DiffGram
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a DiffGram. To make DiffGrams reall
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Figure 10-8: The sample save-and-re
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dv.RowStateFilter = DataViewRowStat
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in the RowError property of the cor
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however, the verbosity of XML paten
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Chapter 11: XML SerializationOvervi
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0As you can see, the class represen
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ead-only properties; does not handl
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}public Employee(){m_ID = -1;}publi
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Methods of the XmlSerializer ClassT
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ns.Add("d", "urn:dino-e-xml");ns.Ad
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When designing classes destined to
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eferenced assembly and its properti
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The preceding code creates an attri
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}public string FirstName;public str
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XML as the type dictates. The attri
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create the XmlSerializer object. Ho
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command, the data flows into the se
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XmlAttributes changesFirstName = ne
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{if (emp.Territories == null)emp.Te
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{// Import type mapping information
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As you can see, the first file crea
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A good source for learning about SO
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NoteSome programmers believe that .
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involved, you must use Web services
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handled by .NET Remoting; the user
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Figure 12-3: How .NET Remoting mars
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If you want to play with the transp
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The query involves three tables—E
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As we saw in Chapter 4, the XmlText
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{// Propertiesprotected SalesDataPr
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We'll look more closely at channels
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server only when the client calls a
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Figure 12-5: The IIS application ma
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this little requirement is enough t
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typeof(ServiceSalesProvider),"tcp:/
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}The code in boldface demonstrates
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BinaryWriter writer = new BinaryWri
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Chapter 13: XML Web ServicesOvervie
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intSOAP is not magic—it is a simp
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public class MyWebService : WebServ
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effectively exposed over the Web, a
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Format of SOAP Messages for a Web M
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The SoapRpcMethod AttributeThe RPC
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If you compare this code with the r
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Figure 13-5: Processing a Web servi
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The machine.config file is an XML f
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Namespace="xmlnet/cs/0735618011")]p
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In situations in which the URL can'
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Const TheYear = 1997' Create the HT
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implementation does make a lot of s
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Mobile code allows you to send C# o
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Chapter 14: XML on the ClientOvervi
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accessible XML parser to consume th
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The following code shows a version
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NoteIn general, you can name the ou
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To create a hidden field, you can u
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To load assemblies from directories
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{}int size = 130;this.Columns.Add(m
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private void PrepareSortedDataView(
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Figure 14-3: An ASP.NET page that c
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var parser = new ActiveXObject("Mic
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"SERVER=localhost;DATABASE=northwin
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Chapter 15: .NET Framework Applicat
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Because we're focusing on applicati
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executable, ASP.NET application or
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NoteUser applications don't need to
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The myfile.config file contains the
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Some internal variablesXmlNodeList
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scratch or inherit from an existing
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Table 15-2: Predefined Section Hand
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The interface includes a single met
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NameValueCollection coll;coll = Con
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}if (configMenu != null)AddMenuTool
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}}menuTools.MenuItems.Add(index, mn
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Implementing the DataSet Section Ha
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AfterwordOverviewWhile writing this
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not an application-specific object.
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