VB.NET and XML XPath and XQuery

VB.NET supports XML processing using the built-in XML classes provided in the .NET Framework. This includes XPath and XQuery, which are query languages used to search and extract data from XML documents.

XPath

XPath is a language used to search and navigate an XML document using path expressions. It provides a way to select parts of an XML document based on the structure of the document.

Syntax

Dim xpathExpression As String
Dim nav As XPath.XPathNavigator = xmlDoc.CreateNavigator()
Dim node As XPath.XPathNodeIterator = nav.Select(xpathExpression)

Here, xpathExpression is the XPath expression used to select nodes in the XML document, xmlDoc is the XML document being queried, and node is the result of the query.

Example

Dim xmlDoc As New XmlDocument()
xmlDoc.Load("data.xml")

Dim xpathExpression As String = "bookstore/book/title"
Dim nav As XPath.XPathNavigator = xmlDoc.CreateNavigator()
Dim node As XPath.XPathNodeIterator = nav.Select(xpathExpression)

While node.MoveNext()
    Console.WriteLine(node.Current.Value)
End While

Output

Everyday Italian
Harry Potter
XQuery Kick Start

Explanation

In the above example, we have loaded an XML document called "data.xml" and used an XPath expression to select all <title> elements located under a <book> element located directly under the <bookstore> element. We then looped through the resulting XPathNodeIterator and printed out the value of each <title> element.

XQuery

XQuery is another language used to search and extract data from XML documents. It uses a syntax similar to SQL and provides more powerful search and selection capabilities than XPath.

Syntax

Dim xqueryExpression As String = "XQuery expression"
Dim xmlDoc As New XmlDocument()
xmlDoc.Load("data.xml")

Dim nav As XPath.XPathNavigator = xmlDoc.CreateNavigator()
Dim node As XPath.XPathNodeIterator = nav.Select(xqueryExpression)

Here, xqueryExpression is the XQuery expression used to select nodes in the XML document, and node is the result of the query.

Example

Dim xmlDoc As New XmlDocument()
xmlDoc.Load("data.xml")

Dim xqueryExpression As String = "for $x in /bookstore/book where $x/price>30 return $x/title"
Dim nav As XPath.XPathNavigator = xmlDoc.CreateNavigator()
Dim node As XPath.XPathNodeIterator = nav.Select(xqueryExpression)

While node.MoveNext()
    Console.WriteLine(node.Current.Value)
End While

Output

Harry Potter
XQuery Kick Start

Explanation

In the above example, we have loaded the same XML document as in the XPath example and used an XQuery expression to select all <title> elements of <book> elements where the <price> element is greater than 30. We then looped through the resulting XPathNodeIterator and printed out the value of each <title> element.

Use

XPath and XQuery are useful for searching and selecting data in XML documents, especially in cases where the XML structure is complex and nested. They can be used to extract data for use in VB.NET applications or to filter and sort data for display.

Important Points

• XPath is used to navigate XML documents based on their structure and path expressions.
• XQuery is used to query XML documents using a syntax similar to SQL.
• Both are useful for searching and selecting data in complex XML documents.

Summary

In summary, VB.NET provides built-in XML support that includes XPath and XQuery for querying and selecting data from XML documents. These languages are useful for searching and extracting data from complex XML structures and can be used to enhance VB.NET applications.