Professional ASP.NET 3.5 in C# and Visual Basic Part 55 pptx

XML Stylesheet Tree Transformations XSLT gained debugging capabilities in Visual Studio 2005, and is improved with new features in Visual Studio 2008, such as XSLT Data Breakpoints and b

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Wor king with XML and LINQ to XML

This is not a book about XML, the eXtensible Markup Language; but XML has become such a part

of an ASP.NET programmer’s life that the topic deserves its own chapter Although most of the

XML functionality in the NET Framework appears to be in theSystem.Xmlnamespace, you can

find XML’s influence throughout the entire Framework includingSystem.DataandSystem.Web

XML is oft maligned and misunderstood To some, XML is simply a text-based markup language; to

others it is an object serialization format or a document-encoding standard In fact, XML has become

the de facto standard manner in which data passes around the Internet XML, however, is not really

a technology as much as it is a set of standards or guiding principles It provides a structure within

which data can be stored; but the XML specification doesn’t dictate how XML processors, parsers,

formatters, and data access methods should be written or implemented.System.Xml,System.Xml

.Linq, and other namespaces contain the NET Framework 3.5’s view on how programmers should

manipulate XML Some of its techniques, such as XSLT and XML Schema, are standards-based

Oth-ers, likeXmlReaderandXmlWriter, started in the world of the NET Framework and now Java has

similar classes The NET Framework 3.5 — along with new compilers for C# 3.0 and VB 9 — brings

LINQ and LINQ to XML as a Language-Integrated Query over XML to the table

This is an ASP.NET book, aimed at the professional Web developer, so it can’t be a book all about

LINQ However, a single chapter can’t do LINQ justice Rather than making this a chapter that

focuses exclusively on justSystem.XmlorSystem.Xml.Linq, this chapter will present the new LINQ

model and syntax as a juxtaposition to the way you’re used to manipulating XML The examples

will include both the traditional and the new LINQ way of doing things We recognize that you

won’t go and rewrite all yourSystem.Xmlcode to use LINQ just because it’s cool, but seeing the

new syntax alongside what you are used to is an excellent way to learn the syntax, and it also

assists you in making decisions on which technology to use going forward

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In this chapter some listings will include a ‘q’ in the numbering scheme These

listings demonstrate how you can use LINQ to XML to accomplish the same task

shown in the previous related listing For example, Listing 10-5q shows the way

you’d accomplish the task from Listing 10-5 using LINQ to XML.

You’ll learn more about LINQ and its flexibility in the all new chapter dedicated to the technology

For the purposes of this chapter, know thatSystem.Xml.Linqintroduces an all new series of objects

such as XDocument and XElement that in some ways complement the existing APIs, but in many ways,

eclipse them You’ll also see how these new classes have provided ‘‘bridges’’ back and forth between

System.XmlandSystem.Xml.Linqthat will enable you to use many new techniques for clearer, simpler

code, while still utilizing the very useful, powerful (and well-tested) features of theSystem.Xmlclasses

you’re used to

Ultimately, however, remember that while the NET Framework has its own unique style of API around

the uses of XML, the XML consumed and produced by these techniques is standards-based and can be

used by other languages that consume XML This chapter covers all the major techniques for

manipulat-ing XML provided by the NET Framework.XmlReaderandXmlWriteroffer incredible speed but may

require a bit more thought The XmlDocument or DOM is the most commonly used method for

manip-ulating XML but you’ll pay dearly in performance penalties without careful use ADO NET DataSets

have always provided XML support, and their deep support continues with NET 3.5 XML Stylesheet

Tree Transformations (XSLT) gained debugging capabilities in Visual Studio 2005, and is improved with

new features in Visual Studio 2008, such as XSLT Data Breakpoints and better support in the editor for

loading large documents Additionally, XSLT stylesheets can be compiled into assemblies even more

easily with the new command-line stylesheet compiler ASP.NET continues to make development easier

with some simple yet powerful server controls to manipulate XML

Its flexibility and room for innovation make XML very powerful and a joy to work with

Note that when the acronym XML appears by itself, the whole acronym is

capitalized, but when it appears in a function name or namespace, only the X is

capitalized, as in System.Xml or XmlTextReader Microsoft’s API Design Guidelines

dictate that if an abbreviation of three or more characters appears in a variable

name, class name, or namespace, the first character is capitalized.

The Basics of XML

Listing 10-1, aBooks.xmldocument that represents a bookstore’s inventory database, is one of the sample

documents used in this chapter This example document has been used in various MSDN examples for

many years

Listing 10-1: The Books.xml XML document

<?xml version=’1.0’?>

<! This file is a part of a book store inventory database >

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<title>The Autobiography of Benjamin Franklin</title>

<first-name>Benjamin</first-name>

<last-name>Franklin</last-name>

</author>

</book>

<title>The Confidence Man</title>

<first-name>Herman</first-name>

<last-name>Melville</last-name>

</author>

</book>

<title>The Gorgias</title>

<first-name>Sidas</first-name>

<last-name>Plato</last-name>

</author>

</book>

</bookstore>

The first line of Listing 10-1, starting with<?xml version=‘1.0’?>, is an XML declaration This line

should always appear before the first element in the XML document and indicates the version of XML

with which this document is compliant

The second line is an XML comment and uses the same syntax as an HTML comment This isn’t a

coincidence; remember that XML and HTML are both descendants of SGML, the Standard Generalized Markup Language Comments are always optional in XML documents

The third line,<bookstore>, is the opening tag of the root element or document entity of the XML

document An XML document can have only one root element The last line in the document is the clos-ing tag</bookstore>of the root element No elements of the document can appear after the final

closing tag</bookstore> The<bookstore>element contains anxmlnsattribute such as

xmlns="http://example.books.com" Namespaces in XML are similar to namespaces in the NET

Framework because they provide qualification of elements and attributes It’s very likely that someone else

in the world has created a bookstore XML document before, and it’s also likely he or she chose an

ele-ment such as<book>or<bookstore/> A namespace is defined to make your<book>element different from any others and to deal with the chance that other<book>elements might appear with yours in the same document — it’s possible with XML

This namespace is often a URL (Uniform/Universal Resource Locator), but it actually can be a URI

(Uniform/Universal Resource Identifier) A namespace can be a GUID or a nonsense string such as

www-computerzen-com:schemaas long as it is unique Recently, the convention has been to use a URL

because URLs are ostensibly unique, thus making the document’s associated schema unique You learn more about schemas and namespaces in the next section

The fourth line is a little different because the<book>element contains some additional attributes such

asgenre,publicationdate, andISBN The order of the elements matters in an XML document, but the

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order of the attributes does not These attributes are said to be on or contained within the book element.

Consider the following line of code:

<book genre="autobiography" publicationdate="1981" ISBN="1-861003-11-0">

Notice that every element following this line has a matching end tag, similar to the example that follows:

<example>This is a test</example>

If no matching end tag is used, the XML is not well formed; technically it isn’t even XML! These next two

example XML fragments are not well formed because the elements don’t match up:

<example>This is a test

<example>This is a test</anothertag>

If the<example>element is empty, it might appear like this:

<example></example>

Alternatively, it could appear as a shortcut like this:

<example/>

The syntax is different, but the semantics are the same The difference between the syntax and the

seman-tics of an XML document is crucial for understanding what XML is trying to accomplish XML documents

are text files by their nature, but the information — the information set — is representable using text that

isn’t exact The set of information is the same, but the actual bytes are not

Note that attributes appear only within start tags or empty elements such as<book

genre="scifi"></book>or<book genre = "scifi" />.Visit the World Wide Web

Consortium’s (W3C) XML site at www.w3.org/XML/ for more detailed information

on XML.

The XML InfoSet

The XML InfoSet is a W3C concept that describes what is and isn’t significant in an XML document The

InfoSet isn’t a class, a function, a namespace, or a language — the InfoSet is a concept

Listing 10-2 describes two XML documents that are syntactically different but semantically the same

Listing 10-2: XML syntax versus semantics

XML document

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<last-name>Franklin</last-name>

</author>

</book>

</bookstore>

XML document that differs in syntax, but not in semantics

<?xml version=’1.0’?><bookstore><book genre="autobiography"

publicationdate="1981" ISBN="1-861003-11-0"><title>The Autobiography of Benjamin

Franklin</title><author><first-name>Benjamin</first-name>

<last-name>Franklin</last-name></author><price/></book></bookstore>

Certainly, the first document in Listing 10-2 is easier for a human to read, but the second document is

just as easy for a computer to read The second document has insignificant white space removed

Notice also that the empty<price/>element is different in the two documents The first uses the verbose

form, whereas the second element uses the shortcut form to express an empty element However, both are

empty elements.

You can manipulate XML as elements and attributes You can visualize XML as a tree of nodes You

rarely, if ever, have to worry about angle brackets or parse text yourself A text-based differences (diff)

tool would report these two documents are different because their character representations are different

An XML-based differences tool would report (correctly) that they are the same document Each document contains the same InfoSet

You can run a free XML Diff Tool online at

http://www.deltaxml.com/free/compare//

XSD–XML Schema Definition

XML documents must be well formed at the very least However, just because a document is well formed doesn’t ensure that its elements are in the right order, have the right name, or are the correct data types

After creating a well-formed XML document, you should ensure that your document is also valid A valid

XML document is well formed and also has an associated XML Schema Definition (XSD) that describes what elements, simple types, and complex types are allowed in the document

The schema for theBooks.xmlfile is a glossary or vocabulary for the bookstore described in an XML

Schema definition In programming terms, an XML Schema is a type definition, whereas an XML docu-ment is an instance of that type Listing 10-3 describes one possible XML Schema calledBooks.xsdthat validates against theBooks.xmlfile

Listing 10-3: The Books.xsd XML Schema

<?xml version="1.0" encoding="utf-8" ?>

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"

xmlns:tns="http://example.books.com"

xmlns="http://example.books.com"

targetNamespace="http://example.books.com"

elementFormDefault="qualified">

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<xsd:element name="bookstore" type="bookstoreType"/>

<xsd:complexType name="bookstoreType">

<xsd:sequence maxOccurs="unbounded">

<xsd:element name="book" type="bookType"/>

</xsd:sequence>

</xsd:complexType>

<xsd:complexType name="bookType">

<xsd:sequence>

<xsd:element name="title" type="xsd:string"/>

<xsd:element name="author" type="authorName"/>

<xsd:element name="price" type="xsd:decimal"/>

</xsd:sequence>

<xsd:attribute name="genre" type="xsd:string"/>

<xsd:attribute name="publicationdate" type="xsd:string"/>

<xsd:attribute name="ISBN" type="xsd:string"/>

</xsd:complexType>

<xsd:complexType name="authorName">

<xsd:sequence>

<xsd:element name="first-name" type="xsd:string"/>

<xsd:element name="last-name" type="xsd:string"/>

</xsd:sequence>

</xsd:complexType>

</xsd:schema>

The XML Schema in Listing 10-3 starts by including a series of namespace prefixes used in the schema

document as attributes on the root element The prefixxsd:is declared on the root element (xmlns:

xsd="http://www.w3.org/2001/XMLSchema") and then used on all other elements of that schema

The default namespace assumed for any elements without prefixes is described by thexmlnsattribute

like this:

xmlns="http://example.books.com"

A namespace-qualified element has a prefix such as<xsd:element> The target namespace for all

elements in this schema is declared with thetargetNamespaceattribute

XML Schema can be daunting at first; but if you read each line to yourself as a declaration, it makes more

sense For example, the line

<xsd:element name="bookstore" type="bookstoreType"/>

declares that an element namedbookstorehas the typebookstoreType Because the

targetNames-pacefor the schema ishttp://example.books.com, that is the namespace of each declared type in the

Books.xsdschema If you refer to Listing 10-1, you see that the namespace of theBooks.xmldocument

is alsohttp://example.books.com

For more detailed information on XML Schema, visit the W3C’s XML Schema site atwww.w3.org/

XML/Schema

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Editing XML and XML Schema in Visual Studio 2008

If you start up Visual Studio 2008 and open theBooks.xmlfile into the editor, you notice immediately

that the Visual Studio editor provides syntax highlighting and formats the XML document as a nicely

indented tree If you start writing a new XML element anywhere, you don’t have access to IntelliSense Even though thehttp://example.books.comnamespace is the default namespace, Visual Studio 2008

has no way to find theBooks.xsdfile; it could be located anywhere Remember that the namespace is not

a URL It’s a URI — an identifier Even if it were a URL it wouldn’t be appropriate for the editor, or any program you write, to go out on the Web looking for a schema You have to be explicit when associating XML Schema with instance documents

Classes and methods are used to validate XML documents when you are working programmatically, but the Visual Studio editor needs a hint to find theBook.xsdschema Assuming theBooks.xsdfile is in the same directory asBooks.xml, you have three ways to inform the editor:

❑ Open theBooks.xsdschema in Visual Studio in another window while theBooks.xmlfile is also open

❑ Include aschemaLocationattribute in the Books.xmlfile

❑ If you open at least one XML file with theschemaLocationattribute set, Visual Studio uses that schema for any other open XML files that don’t include the attribute

❑ Add theBooks.xsdschema to the list of schemas that Visual Studio knows about internally by

adding it to theSchemasproperty in the document properties window of theBooks.xmlfile

When schemas are added in this way, Visual Studio checks the document’s namespace and

determines if it already knows of a schema that matches

TheschemaLocationattribute is in a different namespace, so include thexmlnsnamespace attribute and your chosen prefix for the schema’s location, as shown in Listing 10-4

Listing 10-4: Updating the Books.xml file with a schemaLocation attribute

<! This file is a part of a book store inventory database >

<bookstore xmlns="http://example.books.com"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://example.books.com Books.xsd">

Rest of the XML document omitted for brevity

The format for theschemaLocationattribute consists of pairs of strings separated by spaces where the

first string in each pair is a namespace URI and the second string is the location of the schema The

location can be relative, as shown in Listing 10-4, or it can be anhttp://URL orfile://location

When theBooks.xsdschema can be located for theBooks.xmldocument, Visual Studio 2008’s

XML Editor becomes considerably more useful Not only does the editor underline incorrect elements

with blue squiggles, it also includes tooltips and IntelliSense for the entire document, as shown in

Figure 10-1

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Figure 10-1

Figure 10-2

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When the XML Schema file from Listing 10-3 is loaded into the Visual Studio Editor, the default view

in Visual Studio 2008 for standard XSDs is now the XML Editor, rather than the Dataset Designer as in

Visual Studio 2005 However, if you right-click onBooks.xsdin the Solution Explorer and select Open

With, you’ll get a brief warning that the DataSet Designer might have modified your schema by remov-ing non-dataset XML Make sure your schema is backed up and select OK, and you’ll get a redesigned

Dataset Designer that presents the elements and complex types in a format that is familiar if you’ve

edited database schemas before (see Figure 10-2) This Designer view is intended to manipulate DataSets expressed as schema, but it can be a useful visualizer for many XSDs However, as soon as you use this visualizer to edit your XSD, your document will be turned into a Microsoft DataSet Therefore the Dataset Designer in Visual Studio 2008 is no longer suitable as a general purpose visual XML Schema Editor

A greatly enhanced XSD Designer will be released as an add-on soon after the release of Visual

Stu-dio but wasn’t yet released at the time of this writing This new XML Schema Editor will include a

Schema Explorer toolbox window that will present a comprehensive tree-view of complex schemas in

a much more scalable and appropriate way than can a more traditional ER-Diagram For more details,

see Figure 10-3 or go tohttp://blogs.msdn.com/xmlteam/archive/2007/08/27/

announcing-ctp1-of-the-xml-schema-designer.aspx

Figure 10-3

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After you have created an XML Schema that correctly describes an XML document, you’re ready to start

programmatically manipulating XML TheSystem.XmlandSystem.Xml.Linqnamespaces provide a

number of ways to create, access, and query XML XML Schemas provide valuable typing information

for all XML consumers that are type aware

XmlReader and XmlWriter

XmlReaderoffers a pull-style API over an XML document that is unique to the NET Framework It

pro-vides fast, forward-only, read-only access to XML documents These documents may contain elements

in multiple namespaces.XmlReaderis actually an abstract class that other classes derive from to provide

specific concrete instances likeXmlTextReaderandXmlNodeReader

Things changed slightly withXmlReaderbetween the NET Framework 1.1 and 2.0 although nothing

significant changed in theXmlReaderandXmlWriterclasses in NET 3.5 as most of the new functionality

was around LINQ Since NET 1.1, several convenient new methods have been added, and the way you

createXmlReaderhas changed for the better.XmlReaderhas become a factory The primary way for you

to create an instance of anXmlReaderis by using the Static/SharedCreatemethod Rather than creating

concrete implementations of theXmlReaderclass, you create an instance of theXmlReaderSettingsclass

and pass it to theCreatemethod You specify the features you want for yourXmlReaderobject with the

XmlReaderSettingsclass For example, you might want a specializedXmlReaderthat checks the validity

of an XML document with theIgnoreWhiteSpaceandIgnoreCommentsproperties pre-set TheCreate

method of theXmlReaderclass provides you with an instance of anXmlReaderwithout requiring you

to decide which implementation to use You can also add features to existingXmlReaders by chaining

instances of theXmlReaderclass with each other because theCreatemethod ofXmlReadertakes another

XmlReaderas a parameter

If you are accustomed to using theXmlDocumentor DOM to write an entire XML fragment or

docu-ment into memory, you will find usingXmlReaderto be a very different process A good analogy is

thatXmlReaderis toXmlDocumentwhat the ADO ForwardOnly recordset is to the ADO Static recordset

Remember that the ADO Static recordset loads the entire results set into memory and holds it there

Cer-tainly, you wouldn’t use a Static recordset if you want to retrieve only a few values The same basic rules

apply to theXmlReaderclass If you’re going to run through the document only once, you don’t want to

hold it in memory; you want the access to be as fast as possible.XmlReaderis the right decision in

this case

Listing 10-5 creates anXmlReaderclass instance and iterates forward through it, counting the number of

books in theBooks.xmldocument from Listing 10-1 TheXmlReaderSettingsobject specifies the features

that are required, rather than the actual kind ofXmlReaderto create In this example,

IgnoreWhite-spaceandIgnoreCommentsare set toTrue TheXmlReaderSettingsobject is created with these property

settings and then passed to theCreatemethod ofXmlReader

Listing 10-5: Processing XML with an XmlReader

VB

Imports System.IO

Imports System.Xml

Partial Class _Default

Inherits System.Web.UI.Page

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