This article is a basic introduction to LINQ.
What is the Linq
LINQ uses an SQL-like syntax to make query
expressions well beyond the capabilities of embedded SQL as implemented in
programming languages. LINQ is a set of extensions to the .NET Framework that
encompass language-integrated query, set, and transform operations. It extends
C# and Visual Basic with native language syntax for queries and provides class
libraries to take advantage of these capabilities.
- Linq allows us to query a collection implementing IEnumerable<T> with SQL like syntax.
- We can write condition criteria, do the sorting and so on.
- A Linq query has two parts. The first is data and the other is query operators.
- The data could be an array, a list.
- The operators are defined as static extension methods in
System.Linq.Enumerable. - LINQ also supports data from a remote server, such as a SQL Server.
Lambda and Linq
Most query operators accept a lambda expression as an argument.which provide
developers with a convenient way to write functions that can be passed as
arguments for subsequent evaluation. Lambda expressions are similar to CLR
delegates and must adhere to a method signature defined by a delegate type.
For example
C# code
using
System;
using
System.Collections.Generic;
using
System.Linq;
using
System.Text;
namespace
ConsoleApplication20
{
class Program
{
static void
Main(string[] args)
{
string[] names = {
"VisualBasic", "Java",
"Csharp",
"Javascript" };
IEnumerable<string>
filteredNames = System.Linq.Enumerable.Where(names,
n => n.Length >= 4);
foreach (string
n in filteredNames)
Console.WriteLine(n);
}
}
}
In example above, the lambda expression is as
follows:
n => n.Length >= 4
VB code
Module Module1
Sub Main()
Dim names As String() = {"Visual
Basic", "Java",
"Csharp",
"Javascript"}
Dim filteredNames As IEnumerable(Of String) = System.Linq.Enumerable.Where(names,
Function(n) n.Length>= 4)
For Each n
As String In filteredNames
Console.WriteLine(n)
Next
End Sub
End Module
OUTPUT
Query expression syntax
C# provides another syntax for writing queries, called query expression
syntax.
using
System;
using
System.Collections;
using
System.Collections.Generic;
using
System.Linq;
class Program
{
static void
Main()
{
string[] names = {
"VisualBasic", "Java",
"C#",
"Javascript" };
IEnumerable<string>
filteredNames = from n
in names select n;
foreach (string
name in filteredNames)
Console.WriteLine(name);
}
}
VB code
Module Module1
Sub Main()
Dim names As String() = {"VisualBasic",
"Java", "C#",
"Javascript"}
Dim filteredNames As IEnumerable(Of String) = From n
In names n
For Each name
As String In filteredNames
Console.WriteLine(name)
Next
End Sub
End Module
OUTPUT
Lambda Expressions and Linq Operators
In example below, we are using the following lambda expression to
the Where operator:
n => n.Contains ("a")
The input Input type is string, and the return type is bool.
The lambda expression depends on the particular query operator.
C# code
using
System;
using
System.Collections;
using
System.Collections.Generic;
using
System.Linq;
class Program
{
static void
Main()
{
string[] names = {
"C", "Java",
"C#",
"Javascript" };
IEnumerable<string>
query = names
.Where(n =>
n.Contains("a"))
.OrderBy(n =>
n.Length)
.Select(n =>
n.ToUpper());
foreach (string
name in query)
Console.WriteLine(name);
}
}
VB code
Module Module1
Sub Main()
Dim names As String() = {"C",
"Java", "C#",
"Javascript"}
Dim query As IEnumerable(Of String) = names.Where(Function(n)
n.Contains("a")).OrderBy(Function(n)
n.Length).[Select](Function(n) n.ToUpper())
For Each name
As String In query
Console.WriteLine(name)
Next
End Sub
End Module
OUTPUT
