Introducing LINQ in Visual C#.NET

Maker Denso QR Bar Code in Visual C#.NET Introducing LINQ

more easily perform many of the XML-processing tasks that you have been performing with the traditional XML APIs from the System.Xml namespace. We will first examine why we need an XML API like LINQ to XML by comparing it to some alternatives. You ll then make your first steps with some code using LINQ to XML in an obligatory Hello World example.

XML is ubiquitous nowadays, and is used extensively in applications written using general-purpose languages such as C# or VB.NET. It is used to exchange data between applications, store configuration information, persist temporary data, generate web pages or reports, and perform many other things. It is everywhere! Until now, XML hasn t been natively supported by most programming languages, which therefore required the use of APIs to deal with XML data. These APIs include XmlDocument, XmlReader, XPathNavigator, XslTransform for XSLT, and SAX and XQuery implementations. The problem is that these APIs are not well integrated with programming languages, often requiring several lines of unnecessarily convoluted code to achieve a simple result. You ll see an example of this in the next section (see listing 1.13). But for the moment, let s see what LINQ to XML has to offer. LINQ to XML extends the language-integrated query features offered by LINQ to add support for XML. It offers the expressive power of XPath and XQuery but in our programming language of choice and with type safety and IntelliSense. If you ve worked on XML documents with .NET, you probably used the XML DOM (Document Object Model) available through the System.Xml namespace. LINQ to XML leverages experience with the DOM to improve the developer toolset and avoid the limitations of the DOM. Table 1.2 compares the characteristics of LINQ to XML with those of the XML DOM.

Table 1.2 Comparing LINQ to XML with the XML DOM to show how LINQ to XML is a better value proposition LINQ to XML characteristic Element-centric Declarative model LINQ to XML code presents a layout close to the hierarchical structure of an XML document Language-integrated queries XML DOM characteristic Document-centric Imperative model No resemblance between code and document structure

Comparing LINQ to XML with the XML DOM to show how LINQ to XML is a better value proposition (continued) LINQ to XML characteristic XML DOM characteristic Basic things require a lot of code

Creating elements and attributes can be done in one instruction; text nodes are just strings Simplified XML namespace support

Requires dealing with prefixes and namespace managers Heavyweight and memory intensive Everything is loaded in memory Different ways to work with the various bits of XML documents

Whereas the DOM is low-level and requires a lot of code to precisely formulate what we want to achieve, LINQ to XML provides a higher-level syntax that allows us to do simple things simply. LINQ to XML also enables an element-centric approach in comparison to the document-centric approach of the DOM. This means that we can easily work with XML fragments (elements and attributes) without having to create a complete XML document. Two classes that the .NET Framework offers are XmlReader and XmlWriter. These classes provide support for working on XML text in its raw form and are lower-level than LINQ to XML. LINQ to XML uses the XmlReader and XmlWriter classes underneath and is not a completely new XML API. One advantage of this is that it allows LINQ to XML to remain compatible with XmlReader and XmlWriter. LINQ to XML makes creating documents more direct, but it also makes it easier to query XML documents. Expressing queries against XML documents feels more natural than having to write of lot of code with several loop instructions. Also, being part of the LINQ family of technologies, it is a good choice when we need to join diverse data sources. With LINQ to XML, Microsoft is aiming at 80 percent of the use cases. These cases involve straightforward XML formats and common processing. For the other cases, developers will continue to use the other APIs. Also, although LINQ to XML takes inspiration from XSLT, XPath, and XQuery, these technologies have benefits of their own and are designed for specific use cases, and within those scopes LINQ to XML is in no way able to compete with them. LINQ to XML is not enough for some specific cases, but its compatibility with the other XML APIs allows us to use