An introduction to LINQ to XML

XML stands for Extensible Markup Language. It is a popular markup language that is similar to HTML. It is used for formatting, storing, and transporting data with the help of tags.

LINQ stands for Language Integrated Query. It is a Microsoft .NET Framework technology. It is a set of methods/technologies that provide a consistent way to query data from various resources, such as XML documents and databases. LINQ queries are quite similar to SQL and easy to understand and integrated into .NET languages.

LINQ to XML

LINQ to XML is an extension of LINQ that allows us to manipulate XML documents using LINQ syntax. LINQ to XML works in the following way:

  1. It converts the XML data into LINQ objects.

  2. It manipulates the converted data using LINQ queries.

Working of LINQ
Working of LINQ

So, LINQ to XML allows us to load, query, modify and save an XML document using LINQ syntax. To get familiar with the conversion and syntax of LINQ, we'll go through an example.

Loading a document

LINQ to XML allows us to load the XML document. The XDocument.Load method of XDocument class creates a new XDocument instance using an XML file. We specify the path of our sample XML file and then pass it as a parameter to the load function. 

string xmlFilePath = "student.xml";     //path to the file
XDocument xmlDoc = XDocument.Load(xmlFilePath);

Querying data

LINQ to XML allows us to use LINQ syntax to query XML data. For querying the data, we'll look into the following method of XElement class:

  • The XElement.Descendants method returns the collection of all the descendant elements of an XML element.

var query = from student in xmlDoc.Descendants("student")
            where (string)student.Attribute("grade") == "1"
            select new
            {
                First_Name = student.Element("first_name").Value,
                Last_Name  = student.Element("last_name").Value,
                      Age  = student.Element("age").Value
            };

Modifying data

With LINQ to XML, we can modify XML data by creating and updating elements, attributes, and values. For this, we'll look into the following methods of XElement.

  • The XElement.Add method adds an element as a new child.

// Add a new student element
XElement newStudent = new XElement("student",
                      new XElement("first_name", "Kim"),
                      new XElement("last_name", "Joe"),
                      new XElement("grade", "3"));
xmlDoc.Element("class").Add(newStudent);

  • The XElement.SetValue method updates an existing element or attribute.

// Update a student's age
XElement updateAge = student.Age;
updateAge.SetValue("4");

Saving data

Like querying and modifying, LINQ to XML provides a simple way to save the data. The XDocument.Save method of XDocument class overwrites the XML file if it exists. 

xmlDoc.Save("Student.xml");

You can run the following command to see the updated records in the file student.xml.

cat student.xml

Code example

Press the "Run" button to execute the code:

using System;
using System.Linq;
using System.Xml.Linq;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            // Load the XML file
            string xmlFilePath = "student.xml";  
            XDocument xmlDoc = XDocument.Load(xmlFilePath);
            
            // Query the XML using LINQ
            var query = from student in xmlDoc.Descendants("student")
                        where (string)student.Attribute("grade") == "1"
                        select new
                        {
                            First_Name = student.Element("first_name").Value,
                            Last_Name  = student.Element("last_name").Value,
                                  Age  = student.Element("age").Value
                        };

            // Print the results
            Console.WriteLine("\nPrinting records where grade = 1:");
            foreach (var student in query)
            {
                
                Console.WriteLine($"\n{student.First_Name} , {student.Last_Name} , {student.Age}");

            }

            // Add a new student element
            XElement newStudent = new XElement("student",
                                  new XElement("first_name", "Kim"),
                                  new XElement("last_name", "Joe"),
                                  new XElement("grade", "3"));
            xmlDoc.Element("class").Add(newStudent); 
            Console.WriteLine("\nNew Student has been added");

            // Update a student's age
            var update = from student in xmlDoc.Descendants("student")
                        where (string)student.Attribute("grade") == "2"
                        select new
                        {
                          Age=  student.Element("age")
                        };
 
            foreach (var student in update)
            {
                XElement updateAge = student.Age;
                updateAge.SetValue("4");

            }  
            // save the file
            xmlDoc.Save("student.xml");
            Console.WriteLine("\nUpdated age where grade = 2");
        }
    }
}
Example

Code explanation

  • Lines 12–13: We load our XML file student.xml.

  • Lines 16–32: We fetch the record where grade is equal to 1 and print all those records to the console.

  • Lines 35–40: We add a new student newStudent to the file.

  • Lines 43–55: We update the age of the students using the setValue() method of XElement whose grade is 2.

  • Line 57: We save the updated data in our file student.xml.

Conclusion

LINQ to XML conversion provides us with an easy way to work with XML documents instead of using the traditional complex approach of using DOM.

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