XML DOM Functionality in .NET

1. XML DOM Functionality in .NET DSK Chakravarthy http://dskc.blogspot.com dskcheck@msn.com 94496 12273 http://msmvps.com/blogs/Chakravarthy

2. Agenda • You can see the agenda along the entire presentation • Q&A is at the End of session

3. What I talk about • The basics of reading and writing XML, programmatically • The important classes associated with XML documents in the System.XML namespace • How to Read XML Data • How to Traverse in XML DOM using xPath expressions

4. Are you ready ? • Prerequisites • Basic Understanding of XML • Ability to read code

5. Introduction to XML DOMGetting Started • Many apps need to read/write XML data • Perhaps need to: • Store or retrieve configuration settings • Read/write data stored in XML format • Handle inter-application data transfer • XML programming required for all these • System.Xml.XmlDocument class provides support for handling XML

6. Introduction to XML DOMWhat I’ll cover now • NET Framework uses XML in many ways • Provides several techniques for working with XML • Only cover tree-based, in-memory handling • Other sessions cover other techniques, including the XmlReader/XmlWriter classes

7. Introduction to XML DOM.NET APIs for working with XML • Two main .NET APIs for working with XML: • Cached, read/write, random access • XML Document Object Model (DOM) • Tree-based, in-memory cache • Represented by the XmlDocument class • Non-cached, forward-only, read-only access • Represented by the XmlReader/XmlWriter classes

8. Introduction to XML DOMTree-Based XML Handling 1/4 • Using this API, XML data loaded synchronously into a “tree” • Contains root node, and multiple child nodes • Each XML element corresponds to one or more nodes in the tree • Each node (except root node) has a parent node • Each node (except root node) can have multiple siblings • Each node can have multiple children

9. Introduction to XML DOMTree-Based XML Handling 2/4 • Data loaded into memory • Provides random access to individual nodes • Can search for any node, at will • Tree-based structure represents XML infoset • This is the data stored in the serialized XML format • API doesn’t care about angle brackets and quotes • Just the data and its relationships

10. Introduction to XML DOMTree-Based XML Handling 3/4 • Turns this XML content: <bookstore> <book genre="novel" publicationdate="1997" ISBN="1-861001-57-8"> <title>Pride And Prejudice</title> <author> <first-name>Jane</first-name> <last-name>Austen</last-name> </author> <price>24.95</price> </book> </bookstore>

11. Introduction to XML DOMTree-Based XML Handling 4/4 • Into this data structure bookstore book publication date publication date publication date title author firstname lastname price

12. Introduction to XML DOMNon-Cached XML Handling • Allows for fast access • No waiting for data to load • Requires less overhead • Doesn’t allow random access to data • Data flows to application in the order it appears within the original XML stream • Not covered here

13. Introduction to XML DOMWhat is XML DOM? • To provide standard mechanism for programmatically working with data • W3C proposed a standard API for working with XML • XML Document Object Model is the result • Provides software vendors with API for manipulating XML data • Before .NET, VB developers used MSXML COM component • Now use System.Xml namespace

14. Demonstaration -- 0 investigating a sample file – Grocery store

15. Grocery Store departments Store name department #text Brain’s Groceries department Name = “Fruits” Name = “Breads” Item Item Item Type = “Muffin” Id=“B2” Id=“B1” Name Id=“F1” Name Name #text Wonder Bread #text Blueberry Muffin #text Apple Price Price Price #text 3.99 #text 1.29 #text 0.99 New New Introduction to XML DOMSample file as Datastructure

16. Reading XML DataLoad XML Data • Need to load XML data into an XmlDocument object • Parse persisted XML into tree-based structure in memory • Create instance of XmlDocument object • Call Load method, providing file name • Other alternative means for loading, as well • Work with data in tree-based format • Retrieve OuterXml property to view XML

17. Reading XML DataWorking with Node’s children 1/2 • Calling Load method fills data structure • Single root element, possibly other nodes • Sample root node contains three children • XML declaration (processing instruction) • Comment • GroceryStore document element • XmlDocument inherits from XmlNode class • Document == root node • Use HasChildNodes and ChildNodes

18. Reading XML DataWorking with Node’s children 2/2 • Interesting issues: • No recursion • Just displays information about the immediate children of selected node • Name properties differ • xml, #comment, #text, real names • Checking HasChildNodes is redundant • If your intent is to iterate through the nodes

19. Demonstaration -- 1 Load XML Data Child Nodes Visit All Nodes Elements By Name Text Nodes

20. Working with NodesRetrieve nodes matching Criteria • GetElementsByTagName works well, but limited • For more general criteria, use SelectNodes or SelectSingleNode methods of XmlNode • Can pass XPath query • XPath is powerful, and complex • Can only touch on it here

21. Working with NodesGetting started with xPath 1/2 • xPath expressions "know" where to start looking, based on object whose method you call • Use "//" separator to indicate what follows is a descendant, at any level • Use "/" separator to indicate what follows is a direct descendant

22. Working with NodesGetting started with xPath 2/2 • For example: • //Department//Name • Looks within Department node (at any lower level) for Name (at any level below Department) • Use "*" to look for any element name • To match root node of starting object, simply list the name

23. Working with nodesMore about XPATH 1/2 • To match existence of a child node, • use: //Item[New]/Name • Looks for Item that contains a New element, then matches Name element of the Item • To match existence of an attribute, use: • //Item[@Type] • Looks for a Department node with a Name attribute

24. Working with nodesMore about XPATH 2/2 • To match specific values, use: • //Department[@Name= 'Fruits'] • Once you have the XPath expression, and the retrieved node list, iterate through nodes

25. Working with nodesReference to specific Node • Use XmlNode.SelectSingleNode method • Retrieves reference to first matching node • Best when: • You know there 's only one match • You actually want a relative (parent?) of the node you find

26. Demonstaration -- 2 Select Nodes Select Single Node Find Relatives

27. Working with nodesRetrieve Node attributes • XmlNode.Attributes property retrieves XmlAttributeCollection object • Collection of XmlAttribute objects • Nodes with a name, and a value • If you just want a single attribute • Use GetNamedItem method of Attributes collection • Display all department names? • Name is an attribute of Department element

28. Demonstaration -- 3 Retrieve Attributes Single Attribute

29. XmlDocumentConclusion • Derived from the XmlNodeclass • Represents an entire (in memory) XML document • Supports DOM Level 1 and Level 2 Core functionality • Reading & writing built on top of XmlReader& XmlWriter • Load a document and generate the DOM • Using: URI, file, XmlReader, XmlTextReader or Stream

30. Summary • In this session, we looked into: • How to load XML data into memory, using the XmlDocument class • How to read through XML data • retrieving elements by name • by using XPATH • by relative path • How to deal with node attributes

31. Questions ? • Request you to drop me a line • Doesn’t mean that you forget to post them at B.NET • You can expect reply from both mail & at the discussion thread