[Sample of May 5th] Use XPath to read XML


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Today’s sample demonstrates how to use XPathDocument class to read and manipulate XML files

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This sample project shows how to use XPathDocument class to load the XML file and manipulate. It includes two main parts, XPathNavigator usage and XPath Expression usage. The first part shows how to use XPathNavigator to navigate through the whole document, read its content. The second part shows how to use XPath expression to filter information. 


Running the Sample



Using the Code

Initialize XPathDocument and XPathNavigator instances

XPathNavigator xPathNavigator; 
XPathDocument xPathDoc; 
// Navigate through the whole document. 
// Create a new instance of XPathDocument from a XML file. 
xPathDoc = new XPathDocument("books.xml"); 
// Call CreateNavigator method to create a navigator instance. 
// And we will use this navigator object to navigate through whole document. 
xPathNavigator = xPathDoc.CreateNavigator(); 

Call MoveToRoot and MoveToFirstChild to navigate to the book elements

// Move to the root element. 
           // Catalog element is the first children of the root. 
           // Move to catalog element. 
           // We can know a XML node's type from the NodeType property. 
           // XPathNodeType has Attribute, Element, Namespace and so on. 
           if (xPathNavigator.NodeType == XPathNodeType.Element) 
               // We can know if a Node has child nodes by checking its 
               // HasChildren property. If it returns true, that node has child nodes. 
               if (xPathNavigator.HasChildren == true) 
                   // Move to the first child which is our first book nodes. 

Loop through all books and thier children nodes. Output author, title, genre, price, publish_date, description information for each book.

    // We can know if a node has any attribute by checking 
    // the HasAttributes property. When this property returns 
    // true, we can get the specified attribute by calling 
    // navigator.GetAttribute() method. 
    if (xPathNavigator.HasAttributes == true) 
        Console.WriteLine("Book ID: " + xPathNavigator.GetAttribute("id", "")); 
    // Iterate through a book node's child nodes 
    // and list all child node information, like  
    // name, author, price, publish date and so on. 
    if (xPathNavigator.HasChildren) 
            Console.Write("\t{0}:\t{1}\r\n", xPathNavigator.Name, xPathNavigator.Value); 
        } while (xPathNavigator.MoveToNext()); 
        // When all child nodes are reached. The MoveToNext() method returns 
        // false. Then we need to call MoveToParent to go back to the book level. 
    // Move to the next book element. 
} while (xPathNavigator.MoveToNext()); 

Use XPath Expression to select out the book with ID bk103 and output its detailed information.

// Use XPath Expression to select out book bk103. 
           // The expression should be "/catalog/book[@id='bk103']" 
           // @ means to look id attribute and match bk103. 
           Console.WriteLine("Use XPath Expression to select out the book with ID bk103:"); 
           XPathExpression expression = xPathNavigator.Compile("/catalog/book[@id='bk103']"); 
           XPathNodeIterator iterator = xPathNavigator.Select(expression); 
           // After compile the XPath expression, we can call navigator.Select 
           // to retrieve the XPathNodeIterator. With this interator, we can loop 
           // trough the results filtered by the XPath expression. 
           // The following codes print the book bk103's detailed information. 
           while (iterator.MoveNext()) 
               XPathNavigator nav = iterator.Current.Clone(); 
               Console.WriteLine("Book ID: " + nav.GetAttribute("id", "")); 
               if (nav.HasChildren) 
                       Console.Write("\t{0}:\t{1}\r\n", nav.Name, nav.Value); 
                   } while (nav.MoveToNext()); 

Use XPath Expression to select out all books whose price are more than 10.

// Use XPath to select out all books whose price are more than 10.00 
// '[]' means to look into the child node to match the condition "price > 10". 
Console.WriteLine("\r\nUse XPath Expression to select out all books whose price are more than 10:"); 
expression = xPathNavigator.Compile("/catalog/book[price>10]"); 
iterator = xPathNavigator.Select(expression); 

Use XPath Expression to calculate the average price of all books.

// Use XPath Expression to calculate the average price of all books. 
// Here in XPath, we use the sum, div, and count formula. 
Console.WriteLine("\r\nUse XPath Expression to calculate the average price of all books:"); 
expression = xPathNavigator.Compile("sum(/catalog/book/price) div count(/catalog/book/price)"); 
string averagePrice = xPathNavigator.Evaluate(expression).ToString(); 
Console.WriteLine("The average price of the books are {0}", averagePrice); 

More Information

�� How to navigate XML with the XPathNavigator class by using C#

�� How to query XML with an XPath expression by using C#

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