Linq to xml provides an easy query interface for XML files. In the following example I will demonstrate how to use linq to xml to read and write data from/to xml file, using the file for persistency maintaining a list of objects. linq to xml can be used for storing application settings, storing persistent objects or any other data needs to be saved. Follow the 3 steps to get the picture and see how easy it is:

1. Define the Data Entity
2. Create XML Data File
3. Load/Save the Data…

Lets check out the these three steps for using linq to xml

1. Define the Data Entity

In this example we’ll be dealing with patients, so lets define a Patient class with some attributes:

class Patient
{
    public string EMail { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

2. Create XML Data File

<?xml version="1.0" encoding="utf-8" ?>
<Patients>
  <Patient EMail="LeBron@James.com">
    <FirstName>LeBron</FirstName>
    <LastName>James</LastName>
  </Patient>
  <Patient EMail="Kobe@Bryant.com">
    <FirstName>Kobe</FirstName>
    <LastName>Bryant</LastName>
  </Patient>
  <Patient EMail="Allen@Iverson.com">
    <FirstName>Allen</FirstName>
    <LastName>Iverson</LastName>
  </Patient>
</Patients>

3. Load/Save the data

I Inherited the List<Patient> and add Load/Save methods to it:

class PatietList : List<Patient>
{
    public void Load(string xmlFile)
    {
        XDocument doc = XDocument.Load(xmlFile);     

        var query = from xElem in doc.Descendants("Patient")
                    select new Patient
                    {
                        EMail = xElem.Attribute("EMail").Value,
                        FirstName = xElem.Element("FirstName").Value,
                        LastName = xElem.Element("LastName").Value,
                    };     

        this.Clear();
        AddRange(query);
    }     

    public void Save(string xmlFile)
    {
        XElement xml = new XElement("Patients",
                        from p in this
                        select new XElement("Patient",
                            new XAttribute("EMail", p.EMail),
                            new XElement("FirstName", p.FirstName),
                            new XElement("LastName", p.LastName)));     

        xml.Save(xmlFile);     

    }     

}

See how easy this is? get familiar with the XDocument, XElement and XAttribute classes.

Another thing you could do is to move load/save knowledge into the Data object:

class Patient
{
    ...
    public Patient(XElement xElement)
    {
        EMail = xElement.Attribute("EMail").Value;
        FirstName = xElement.Element("FirstName").Value;
        LastName = xElement.Element("LastName").Value;
    }     

    public XElement XElement
    {
        get
        {
            return new XElement("Patient",
                    new XAttribute("EMail", EMail),
                    new XElement("FirstName", FirstName),
                    new XElement("LastName", LastName));
        }
    }
    ...
}

and than the load/save query looks like this:

public void Load(string xmlFile)
{
    ...
    var query = from xElem in doc.Descendants("Patient")
                select new Patient(xElem);
    ...     

public void Save(string xmlFile)
{
    ...
    XElement xml = new XElement("Patients",
                    from p in this
                    select p.XElement);