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Chapter 2: XML ReadersIn the Microsoft .NET Framework, two distinct sets of classes provide for XML-drivenreading and writing operations. These classes are known globally as XML readers andwriters. The base class for readers is XmlReader, whereas XmlWriter provides the baseprogramming interface for writers. In this chapter, we'll focus on a particular type ofXML readers—the XML text readers. In Chapter 3, we'll zero in on validating readersand then move on to XML writers in Chapter 4.The Programming Interface of ReadersXmlReader is an abstract class available from the System.Xml namespace. It definesthe set of functionalities that an XML reader exposes to let developers access an XMLstream in a noncached, forward-only, read-only way.An XML reader works on a read-only stream by jumping from one node to the next in aforward-only direction. The XML reader maintains an internal pointer to the currentnode and its attributes and text but has no notion of previous and next nodes. You can'tmodify text or attributes, and you can move only forward from the current node. If youare visiting attribute nodes, however, you can move back to the parent node or accessan attribute by index. The visit takes place in node-first order, but other visitingalgorithms can be arranged in custom reader classes. See the note on page 72 formore information about visiting algorithms.The specification for the XmlReader class recommends that any derived class shouldcheck at least whether the XML source is well-formed and throw exceptions if an erroris encountered. XML exceptions are handled through the tailor-made XmlExceptionclass. The XMLReader class specification does not say anything about XML validation.Throughout this chapter, you'll see that the .NET Framework provides several readerclasses with and without validation capabilities. Valid sources for an XML reader aredisk files as well as any flavor of .NET streams and text readers (for example, stringreaders).An OOP RefresherThroughout this book, I'll often use terms such as interface and class, sometimesqualified by helper adjectives such as abstract or base. Although a full explanation ofthese terms and their related object-oriented programming (OOP) concepts is beyondthe scope of this book, a quick terminology refresher will help you get to the heart ofthe XML class hierarchy in the .NET Framework.In the .NET Framework, an interface is a container for a named collection of method,property, and event definitions referred to as a contract An interface can be used as areference type, but it is not a creatable type. Other types can implement one or moreinterfaces. In doing so, they adhere to the interface's contract and agree to provideactual implementation for all the methods, properties, and events in the contract.A class is a container that can include data and function members (methods,properties, events, operators, and constructors). Classes support inheritance fromother classes as well as from interfaces. Any class from which another class inherits iscalled a base class.An abstract class simply declares its members without providing any implementation.Like interfaces, abstract classes are not creatable but can be used as reference types.An abstract class differs from an interface in that it has a slightly richer set of internalmembers (constructors, constants, and operators). Members of an abstract class canbe scoped as private, public, or protected, whereas members of an interface aremostly public. In addition, child classes can implement multiple interfaces but caninherit from only one class.21
The XmlReader ClassThe XmlReader class defines methods that enable you to pull data from an XML sourceand to skip unwanted nodes. Bear in mind that each and every element in an XMLstream is considered a node, meaning that node is a rather generic concept thatapplies to subtree roots as well as to attributes, processing instructions, entities,comments, and plain text.The XmlReader class includes methods for reading XML content from an entire text file,returning the depth of the current XML node's subtree, and determining whether thecontents of a given element is empty. You can also fairly easily read and navigateattributes and skip over elements and their contents. Valuable information such as thename and the contents of the current node is also returned via ad hoc properties.Base Properties of XML ReadersTable 2-1 lists the public properties exposed by the XmlReader class. Notice that thevalues these properties contain depend on the actual reader class you are using in yourcode. The description of each property refers to the property's intended goal, but thisdescription might not entirely reflect the actual role of the property in a derived readerclass.Table 2-1: Public Properties of the XmlReader ClassPropertyAttributeCountBaseURICanResolveEntityDepthEOFHasAttributesHasValueIsDefaultIsEmptyElementItemLocalNameNameNamespaceURINameTableNodeTypeDescriptionGets the number of attributes on the current node.Gets the base URI of the current node.Gets a value indicating whether the reader can resolveentities.Gets the depth of the current node in the XMLdocument.Indicates whether the reader has reached the end ofthe stream.Indicates whether the current node has any attributes.Indicates whether the current node can have a value.Indicates whether the current node is an attribute thatoriginated from the default value defined in thedocument type definition (DTD) or schema.Indicates whether the current node is an emptyelement with no attributes or value.Indexer property that returns the value of the specifiedattribute.Gets the name of the current node with any prefixremoved.Gets the fully qualified name of the current node.Gets the namespace URI of the current node. Appliesto Element and Attribute nodes only.Gets the name table object associated with the reader.(More on name table objects later.)Gets the type of the current node.22
Page 2 and 3: Applied XML Programming for Microso
Page 4 and 5: services. Rainer Heller of Siemens
Page 6 and 7: IntroductionIt was about five years
Page 8 and 9: What Do I Need to Use This Book?Mos
Page 10 and 11: Part I: XML Core Classes in the .NE
Page 12 and 13: Related XML StandardsTable 1-1 list
Page 14 and 15: XMLDOM model (memory footprint and
Page 16 and 17: ⋮A configuration section handler
Page 18 and 19: managed application, you must first
Page 20 and 21: Figure 1-1: Streams can be read and
Page 22 and 23: abstraction and explicitly indicate
Page 24 and 25: The XPath Query EngineXPath is a la
Page 28 and 29: Table 2-1: Public Properties of the
Page 30 and 31: Table 2-3: Public Methods of the Xm
Page 32 and 33: Table 2-4: Types of Nodes in the Xm
Page 34 and 35: To produce these results, I created
Page 36 and 37: In particular, the XmlConvert class
Page 38 and 39: The method we create to do this is
Page 40 and 41: Consider the following attribute va
Page 42 and 43: An entity reference consists of the
Page 44 and 45: The NameTable ObjectOne of the secr
Page 46 and 47: End ClassByVal type As XmlNodeType)
Page 48 and 49: Fragments and Parser ContextThe con
Page 50 and 51: You can specify other settings for
Page 52 and 53: FullerAndrewSales ManagerLeverlingJ
Page 54 and 55: String[] m_headerValues;tokensbool
Page 56 and 57: get{if(m_readState != ReadState.Int
Page 58 and 59: }public override string this[string
Page 60 and 61: }}return false;The name of the attr
Page 62 and 63: dt.Columns.Add(col);}reader.MoveToE
Page 64 and 65: Readers and XML ReadersTo cap off o
Page 66 and 67: Chapter 3: XML Data ValidationOverv
Page 68 and 69: The XmlValidatingReader Programming
Page 70 and 71: The ValidationEventHandler EventThe
Page 72 and 73: Figure 3-1: The sample application
Page 74 and 75: 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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s:rowbaseAfter you create the node
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features than the XslTransform clas
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Don't confuse the Internet Explorer
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Supported languages are C#, Visual
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double CalculateSubTotal(XPathNodeI
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profitable, because XML is a metala
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Chapter 8: XML and DatabasesOvervie
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Framework applications. SQLXML 3.0
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......The FOR XML AUTO mode always
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Figure 8-1: The client-side XML for
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lastname AS [Employee!1!Name]This s
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sql:field="FirstName" type="xsd:str
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to instantiate a COM object, query
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}// Process elementswhile(reader.Re
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(No context information specified)X
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}...The base class is for the most
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public override void Close(){m_data
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Synchronizing with a DataSet Object
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denote insertions, deletions, and u
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schema information to associate the
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This schema first defines a relatio
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that throughout the Updategram. The
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object for XML-driven updates, an A
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Table 8-2: Properties of the SqlXml
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Table 8-4: Methods of the SqlXmlCom
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This schema addresses a layout such
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database. If all goes well, the Dat
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Chapter 9: ADO.NET XML Data Seriali
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provided way to serialize ADO.NET o
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1DavolioNancy⋮106897⋮Basically,
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The element describes the body of
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Serializing to Valid XMLAs you can
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Table 9-3: The MappingType Enumerat
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⋮This syntax is simple and effect
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By using keyref and nested types, y
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Figure 9-6: An application that pas
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{}DataTable dt = CreateTempTable(dv
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dt = (DataTable) bf.Deserialize(sr.
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more valuable, because it automatic
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Loading DataSet Objects from XMLThe
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The XML source is read one node aft
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Figure 9-10: ReadXml correctly reco
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Figure 9-12: How Microsoft Visual S
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The reader tracks the current node
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}m_currentAttributeIndex = -1;When
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persistence, resort to the DiffGram
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......The root node can have up to
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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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