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

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Updategrams have been designed to provide three levels of protection against this kindof conflict, as follows:• Blind updates You specify only the primary key of the record in the block. In this case, the change is persisted without firstchecking whether the current status of the record is consistent with theexpected one.• Partial conflict detection The block contains the primary keyas well as any other field you plan to update. When the Updategramexecutes, the change is applied only if the specified fields haven't beenchanged in the meantime.• Total conflict detection All the columns in the row are checked, andthe change fails if any of them has been modified. You can obtain thisform of protection either by listing all the fields in the block orby using the table timestamp column, if one exists. A timestamp columnwill be updated whenever a user writes something to the row.Updategrams and DiffGramsIf you're familiar with ADO.NET, you'll no doubt notice a close similarity, bothconceptual and physical, between Updategrams and DiffGrams. Although ADO.NETDiffGrams are a newer format—and perhaps the format of the future—currently, SQLServer 2000 natively supports only Updategrams.In the section "SQLXML Managed Classes," on page 386, we'll take a quick tour of themanaged classes in SQLXML 3.0. You'll notice that some of these classes apparentlyenable you to send DiffGrams to SQL Server. Although this is possible, the actualimplementation is not particularly effective. The source DiffGram is in fact internallytransformed into an Updategram and then processed by SQL Server.Apart from the patent similarity in their schemas, Updategrams and DiffGrams haveslightly different goals. Updategrams have been designed to update SQL Server;DiffGrams are mostly a stateful way to persist the contents of a DataSet object.(ADO.NET DiffGrams are covered in Chapter 10.) Converting DiffGrams toUpdategrams is certainly possible at the schema level, but Updategrams areunquestionably more powerful objects. Together with SQLXML 3.0 and the SQL ServerXML extensions, Updategrams let you control concurrency, control the order ofupdates, perform transactional updates, and specify parameters.On the other hand, there is not yet a .NET Framework class that works like anUpdategram. (And SQLXML 3.0 is still a hybrid, half COM and half managed code.)Most of the batch update features you find in Updategrams can be implemented inADO.NET using the DataSet object's Update method and the provider-specific dataadapter object. Nothing comes for free, though, and you must write a lot of code toemulate Updategrams in the .NET Framework.XML Batch UpdateIn ADO.NET, as well as in ADO, you can persist the changes made to a set of recordsstored in memory using a procedure called a batch update. This procedure consists ofa loop that looks up for changed records in the DataSet object (or the Recordsetobject in ADO) and issues a command to the back-end database. From theprogrammer's perspective, a batch update is ideal for working in disconnectedscenarios and in ADO.NET—although it is not yet perfect, it has been significantlyimproved and made applicable to real-world usage.Thanks to the ADO.NET XML serialization mechanism (see Chapter 9), you can loada DataSet object from XML data, enter the needed changes, and then proceed withthe batch update. The ADO.NET DiffGram is one of the possible XML representationsfor a DataSet object. Although, all in all, the Updategram is a more powerful and richer313
object for XML-driven updates, an ADO.NET batch update is still an option to considerwhen you're updating a database starting with XML data.The ADO.NET batch update is a step-by-step procedure implemented through asequence of individual statements, all running from the client environment. Onceagain, this is different from Updategrams, in which all data is downloaded to SQLServer and applied as a server-side batch.The closest you can get to this model with ADO.NET is using a datatier componentthat decouples any middle-tier objects from the database. The middle-tier objectapplies all the needed changes to the DataSet object and then passes the object on toanother component, possibly located on the same machine as SQL Server. TheDataSet object is remoted as XML and is rebuilt at the destination. Finally, thechanges are applied in batch update mode but through a specialized and scalabledatatier component and with a more effective use of the bandwidth.SQLXML Managed ClassesSQLXML 3.0 comes with a handful of managed classes designed to expose thefunctionality of SQLXML 3.0 inside the .NET Framework. SQLXML managed classesallow you bring XML data read from SQL Server into .NET Framework applications,process the data, and send any updates back to SQL Server as an ADO.NET DiffGram.The managed classes are exposed by the microsoft.data.sqlxml assembly.SQLXML does not get along perfectly with the .NET Framework data provider for SQLServer. SQLXML needs to address special XML-driven functionalities of SQL Server2000 that the .NET Framework data provider simply does not support. As a result, theSQL Server .NET Framework provider can handle traditional SQL queries, includingFOR XML queries, but it can't execute XML templates (for example, Updategrams) orserver-side XPath queries over XML views. For this reason, SQLXML managed classesrely on the SQLXMLOLEDB OLE DB provider for all of the tasks that involve a SQLServer connection.Figure 8-5 illustrates the key role that the SqlXmlCommand class and itsExecuteStream method play in the overall SQLXML 3.0 architecture.314
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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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Page 287 and 288: Chapter 8: XML and DatabasesOvervie
Page 289 and 290: Framework applications. SQLXML 3.0
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Page 293 and 294: Figure 8-1: The client-side XML for
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object's tables. The data written o
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different blocks. Attributes in the
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If no match is found, ReadXml deduc
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Although this solution is clearly n
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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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