Linq to Xml (Code Snippets)

Linq to Xml enables you to query an Xml document using the familiar LINQ syntax. Linq to Xml features and found within System.Xml.Linq namespace.
System.Xml.Linq introduces a series of objects such as XDocument, XElement and XAttributes which makes creating XML document a breeze.

XAttribute
private void btnXElement_Click(object sender, RoutedEventArgs e)
{
XElement xe = new XElement(new XElement("Shalvin",
new XElement("Students",
new XElement("Name", "Shalvin"))));
textBox1.Text = xe.ToString();

}


XElement

using System.Xml.Linq;

private void Form1_Load(object sender, EventArgs e)
{
XElement xml = new XElement("contacts",
new XElement("contact",
new XAttribute("contactId", "2"),
new XElement("firstName", "Shalvin"),
new XElement("lastName", "PD")
),
new XElement("contact",
new XAttribute("contactId", "3"),
new XElement("firstName", "Praseed"),
new XElement("lastName", "Pai")
)
);
textBox1.Text = xml.ToString();
}

XDocument

using System.Xml.Linq;

protected void Page_Load(object sender, EventArgs e)
{
XDocument xd = new XDocument();
XElement contacts =
new XElement("contacts",
new XElement("contact",
new XElement("name", "Shalvin"),
new XElement("Location", "Kochi")
),
new XElement("contact",
new XElement("name", "Viju"),
new XElement("Location", "Trichur")
)
);
xd.Add(contacts);
xd.Save("c:\\Shalvin.xml");
System.Diagnostics.Process.Start("iexplore", "c:\\Shalvin.xml");
}

Output

<?xml version="1.0" encoding="utf-8"?>
<contacts>
<contact contactId="2">
<firstName>Shalvin</firstName>
<lastName>P D</lastName>
</contact>
<contact contactId="3">
<firstName>Praseed</firstName>
<lastName>Pai</lastName>
</contact>
</contacts>

XDocument Parse

private void button3_Click(object sender, RoutedEventArgs e)
{
XDocument xd = XDocument.Parse(@"<contacts>
<contact contactId='2'>
<firstName>Shalvin</firstName>
<lastName>P D</lastName>
</contact>
<contact contactId='3'>
<firstName>Praseed</firstName>
<lastName>Pai</lastName>
</contact>
</contacts>");

textBox1.Text = xd.ToString();

}

Querying an Xml Document














using System.Xml.Linq;
private void Form1_Load(object sender, EventArgs e){
XDocument xmlFile = XDocument.Load("c:\\Shalvin.xml");
var query = from c in xmlFile.Elements("contacts").Elements("contact").Elements("name")
select c;
foreach (XElement nam in query)
{
listBox1.Items.Add(nam);
}
}

Related Blogs
Linq to Objects
Linq to Sql
.Net Working with Xml

Linq to Objects

LINQ (Language Integrated Query) is a Microsoft .NET framework component that adds native data querying capabilities to C# and Visual Basic .NET (VB.NET) programming languages.
It allows developers to write database-like queries against various data sources including in-memory objects, SQL databases, and XML data sources.
LINQ enables developers to perform queries in a more concise, readable and expressive way, compared to traditional loops and conditional statements.
This blog assumes that you are know Type Inference in C#, Generics and Collection Initializer.

private void Form1_Load(object sender, EventArgs e)
{
List<string> interests = new List<string>{"Music", "Singing", "Swimming"};
var result = from w in interests
where w.Contains("ing")
select w;

foreach (string s in result)
listBox1.Items.Add(s);
}

Lambda

protected void btnLambda_Click(object sender, EventArgs e)
{
   List<string> interests = new List<string>{"Music", "Singing", "Swimming"};
   var result = interests.Where(p => p.Contains("ing"));
        
   foreach (string s in result)
     ListBox1.Items.Add(s);
}

The Linq query retrives all values form Generic List that ends with "ing". You can use Linq with any objects that implements IEnumerable or Generic IEnumerable interface.

StartsWith

private void btnStartsWith_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = from p in interests
            where p.StartsWith("M")
            select p;
foreach (string s in ms)
    listBox1.Items.Add(s);
}

EndsWith

private void btnEndWith_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = from p in interests
            where p.EndsWith("g")
            select p;
foreach (string s in ms)
    listBox1.Items.Add(s);
}

Equals

private void btnEquals_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = from p in interests
            where p.Equals("Music")
            select p;
foreach (string s in ms)
    listBox1.Items.Add(s);
}

First
First can be used to extract only the first item in the collection.

private void btnFirst_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = (from p in interests
            select p).First();
listBox1.Items.Add(ms);
}

Last

private void btnLast_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = (from p in interests
            select p).Last();
listBox1.Items.Add(ms);
}

Count
Using the Count operator I am taking a counts of items inside the Generic List. I will get a value 3.

private void btnCount_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = (from p in interests
            select p).Count();
listBox1.Items.Add(ms);
}

Count of EndsWith
Here I am taking a count of items ending with "ing". I will get an output of 2 ie. the count of "Swimming" and "Singing".

private void btnCountEndWithIng_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = (from p in interests
          where p.EndsWith("ing")  
          select p).Count();
listBox1.Items.Add(ms);
}

Count Equals

private void btnCountEquals_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var ms = (from p in interests
where p.Equals("Music")
          select p).Count();
listBox1.Items.Add(ms);
}

Linq and Generic List of Integer
Having seen working with Generic List of string let's turn out attention to Generic List of Inteters. 

List<int> gliMarks = new List<int> { 98, 56, 88, 79, 96 };

GreaterThan Operator

private void btnShowGreaterThan90_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var G90 = from p in gliMarks
    where p > 90
    select p;
listBox1.ItemsSource = G90;
}

Sum

private void btnSum_Click(object sender, RoutedEventArgs e)
{
    listBox1.Items.Clear();
           
    var vSum = (from p in gliMarks
                select p).Sum();
    listBox1.Items.Add(vSum);
}

Average

private void btnAverage_Click(object sender, RoutedEventArgs e)
{
    listBox1.Items.Clear();
    var Avg = (from p in gliMarks
                    select p).Average();
    listBox1.Items.Add(Avg);
}

Max

private void btnMaximum_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var Maxi = (from p in gliMarks
            select p).Max();
listBox1.Items.Add(Maxi);
}

Or

private void btnSOr_Click(object sender, RoutedEventArgs e)
{
listBox1.Items.Clear();
var vOr = from p in gliMarks
    where p== 98 | p == 88 
    select p;
listBox1.ItemsSource = G90;
}

Linq on Collection of Objects

class Session
{
public string Speaker { get; set; }
public string SessionName { get; set; }
}

List<Session> glSessions = new List<Session>{
new Session{Speaker = "Shalvin P D", SessionName= "Entity Framework 4"},
new Session{Speaker="Arun Kumar", SessionName="Powershell"}};

var G = from p in glSessions
where p.Speaker == "Shalvin P D"
select new { p.Speaker, p.SessionName };


dataGrid1.ItemsSource = G.ToList();
}

LINQ to Sql

I am going to demonstrate LINQ to Sql by writing code.

Support you have a table called Categories in Shalvin database you need to first create a Entity. An Entity is a class that represents a Table or a view in the database.

Create a class as follows:
Set a reference to Data.Linq.

using System.Data.Linq.Mapping;

[Table]
public class Categories
{
[Column(IsPrimaryKey=true, IsDbGenerated=true)]
public int CategoryId { get; set; }

[Column]
public string CategoryName { get; set; }

[Column]
public string Description { get; set; }
}

Each property should have Column Atribute. I am also setting values of IsPrimaryKey and IsDbGenerated for CategoryId column. Editing is possible only if IsPrimaryKey is set to true. IsDbGenerated Indicated that it is an Identity column.


In the asp .net page :

using System.Data.Linq;
protected void Page_Load(object sender, EventArgs e)
{
string ConString = "Integrated Security=sspi;Initial Catalog=Shalvin";
DataContext db = new DataContext(ConString);
var tMovies = db.GetTable<categories>();
GridView1.DataSource = tMovies;
DataBind();
}Now suppose you are interested only in viewing the Categories table with CategoryName 'Confections'.

GridView1.DataSource = tMovies.Where(m => m.CategoryName.Contains("Beverages"));The DataContext is the source of all entities mapped over a database connection. It tracks changes that you made to all retrieved entities .

Linq to Sql with Visual Studio Tools

Having seen the internals lets turn our attention to the Visual Studio Support of Linq to Sql.
Here I have started an Empty Visual Studio Project and Added a Linq to Sql Classes from the Add New Item Dialog. I have renamed it AirLines.dbml

On to the design surface it is possible to drag the table from Database Explorer.

That's all I have to do and I am ready to do CRUD operation with the selected tables.

AirLinesDataContext context = new AirLinesDataContext();
protected void Page_Load(object sender, EventArgs e)
{
  if (!IsPostBack)
  {
    GridView1.DataSource = context.Locations;

    DropDownList1.DataSource = context.Locations;
    DropDownList1.DataTextField = "LocationName";
    DropDownList1.DataValueField = "LocationId";

    DataBind();
  }
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
  Response.Write(DropDownList1.SelectedValue.ToString());
}

protected void btnInsertLocation_Click(object sender, EventArgs e)
{
  var loc = new Location { LocationName = "London", Latitude =67 };
  context.Locations.InsertOnSubmit(loc);
  context.SubmitChanges();
}

Related Blogs
Linq to Objects
Linq to Xml (Code Snippets)