Linq in C#

LINQ
The acronym LINQ stands for Language Integrated Query. Microsoft’s query
language is fully integrated and offers easy data access from in-memory
objects, databases, XML documents, and many more. It is through a set of
extensions, LINQ ably integrates queries in C# and Visual Basic. This
tutorial offers a complete insight into LINQ with ample examples and
coding. The entire tutorial is divided into various topics with subtopics that a
beginner can be able to move gradually to more complex topics of LINQ.
Developers across the world have always encountered problems in querying
data because of the lack of a defined path and need to master a multiple of
technologies like SQL, Web Services, XQuery, etc.
Introduced in Visual Studio 2008 and designed by Anders Hejlsberg, LINQ
(Language Integrated Query) allows writing queries even without the
knowledge of query languages like SQL, XML etc. LINQ queries can be
written for diverse data types.
Example of a LINQ query
C#
using System;
using System.Linq;
class Program {
static void Main() {
string[] words = {"hello", "wonderful", "LINQ", "beautiful", "world"};
//Get only short words
var shortWords = from word in words where word.Length <= 5 select word;

//Print each word out
foreach (var word in shortWords) {
Console.WriteLine(word);
}
Console.ReadLine();
}
}
VB
Module Module1
Sub Main()
Dim words As String() = {"hello", "wonderful", "LINQ", "beautiful",
"world"}
' Get only short words
Dim shortWords = From word In words _ Where word.Length <= 5 _ Select word
' Print each word out.
For Each word In shortWords
Console.WriteLine(word)
Next
Console.ReadLine()
End Sub
End Module

When the above code of C# or VB is compiled and executed, it produces the
following result −
hello
LINQ
world
Syntax of LINQ
There are two syntaxes of LINQ. These are the following ones.
Lamda (Method) Syntax
var longWords = words.Where( w ⇒ w.length > 10);
Dim longWords = words.Where(Function(w) w.length > 10)
Query (Comprehension) Syntax
var longwords = from w in words where w.length > 10;
Dim longwords = from w in words where w.length > 10
Types of LINQ
The types of LINQ are mentioned below in brief.
 LINQ to Objects
 LINQ to XML(XLINQ)
 LINQ to DataSet
 LINQ to SQL (DLINQ)
 LINQ to Entities
Apart from the above, there is also a LINQ type named PLINQ which is
Microsoft’s parallel LINQ.
LINQ Architecture in .NET
LINQ has a 3-layered architecture in which the uppermost layer consists of
the language extensions and the bottom layer consists of data sources that
are typically objects implementing IEnumerable <T> or IQueryable <T>
generic interfaces. The architecture is shown below.

Query Expressions
Query expression is nothing but a LINQ query, expressed in a form similar
to that of SQL with query operators like Select, Where and OrderBy. Query
expressions usually start with the keyword "From".
To access standard LINQ query operators, the namespace System.Query
should be imported by default. These expressions are written within a
declarative query syntax which was C# 3.0.
Below is an example to show a complete query operation which consists of
data source creation, query expression definition and query execution.

C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Operators {
class LINQQueryExpressions {
static void Main() {
// Specify the data source.
int[] scores = new int[] { 97, 92, 81, 60 };
// Define the query expression.
IEnumerable<int> scoreQuery = from score in scores where score > 80
select score;
// Execute the query.
foreach (int i in scoreQuery) {
Console.Write(i + " ");
}
Console.ReadLine();
}
}
}

When the above code is compiled and executed, it produces the following
result −
97 92 81
Extension Methods
Introduced with .NET 3.5, Extension methods are declared in static classes
only and allow inclusion of custom methods to objects to perform some
precise query operations to extend a class without being an actual member
of that class. These can be overloaded also.
In a nutshell, extension methods are used to translate query expressions
into traditional method calls (object-oriented).
Difference between LINQ and Stored Procedure
There is an array of differences existing between LINQ and Stored
procedures. These differences are mentioned below.
 Stored procedures are much faster than a LINQ query as they follow an
expected execution plan.
 It is easy to avoid run-time errors while executing a LINQ query than in
comparison to a stored procedure as the former has Visual Studio’s
Intellisense support as well as full-type checking during compile-time.
 LINQ allows debugging by making use of .NET debugger which is not in case
of stored procedures.
 LINQ offers support for multiple databases in contrast to stored procedures,
where it is essential to re-write the code for diverse types of databases.
 Deployment of LINQ based solution is easy and simple in comparison to
deployment of a set of stored procedures.
Need For LINQ
Prior to LINQ, it was essential to learn C#, SQL, and various APIs that bind
together the both to form a complete application. Since, these data sources

and programming languages face an impedance mismatch; a need of short
coding is felt.
Below is an example of how many diverse techniques were used by the
developers while querying a data before the advent of LINQ.
SqlConnection sqlConnection = new SqlConnection(connectString);
SqlConnection.Open();
System.Data.SqlClient.SqlCommand sqlCommand = new SqlCommand();
sqlCommand.Connection = sqlConnection;
sqlCommand.CommandText = "Select * from Customer";
return sqlCommand.ExecuteReader (CommandBehavior.CloseConnection)
Interestingly, out of the featured code lines, query gets defined only by the
last two. Using LINQ, the same data query can be written in a readable
color-coded form like the following one mentioned below that too in a very
less time.
Northwind db = new Northwind(@"C:DataNorthwnd.mdf");
var query = from c in db.Customers select c;
Advantages of LINQ
LINQ offers a host of advantages and among them the foremost is its
powerful expressiveness which enables developers to express declaratively.
Some of the other advantages of LINQ are given below.
 LINQ offers syntax highlighting that proves helpful to find out mistakes
during design time.
 LINQ offers IntelliSense which means writing more accurate queries easily.
 Writing codes is quite faster in LINQ and thus development time also gets
reduced significantly.

 LINQ makes easy debugging due to its integration in the C# language.
 Viewing relationship between two tables is easy with LINQ due to its
hierarchical feature and this enables composing queries joining multiple
tables in less time.
 LINQ allows usage of a single LINQ syntax while querying many diverse data
sources and this is mainly because of its unitive foundation.
 LINQ is extensible that means it is possible to use knowledge of LINQ to
querying new data source types.
 LINQ offers the facility of joining several data sources in a single query as
well as breaking complex problems into a set of short queries easy to
debug.
 LINQ offers easy transformation for conversion of one data type to another
like transforming SQL data to XML data.
LINQ To SQL
LINQ to SQL offers an infrastructure (run-time) for the management of
relational data as objects. It is a component of version 3.5 of the .NET
Framework and ably does the translation of language-integrated queries of
the object model into SQL. These queries are then sent to the database for
the purpose of execution. After obtaining the results from the database,
LINQ to SQL again translates them to objects.
Introduction of LINQ To SQL
For most ASP.NET developers, LINQ to SQL (also known as DLINQ) is an
electrifying part of Language Integrated Query as this allows querying data
in SQL server database by using usual LINQ expressions. It also allows to
update, delete, and insert data, but the only drawback from which it suffers
is its limitation to the SQL server database. However, there are many
benefits of LINQ to SQL over ADO.NET like reduced complexity, few lines of
coding and many more.

Below is a diagram showing the execution architecture of LINQ to SQL.
How to Use LINQ to SQL?
Step 1 − Make a new “Data Connection” with database server. View
&arrar; Server Explorer &arrar; Data Connections &arrar; Add Connection

Step 2 − Add LINQ To SQL class file

Step 3 − Select tables from database and drag and drop into the new LINQ
to SQL class file.

Step 4 − Added tables to class file.

Querying with LINQ to SQL
The rules for executing a query with LINQ to SQL is similar to that of a
standard LINQ query i.e. query is executed either deferred or immediate.
There are various components that play a role in execution of a query with
LINQ to SQL and these are the following ones.
 LINQ to SQL API − requests query execution on behalf of an application
and sent it to LINQ to SQL Provider.
 LINQ to SQL Provider − converts query to Transact SQL(T-SQL) and sends
the new query to the ADO Provider for execution.
 ADO Provider − After execution of the query, send the results in the form
of a DataReader to LINQ to SQL Provider which in turn converts it into a
form of user object.

It should be noted that before executing a LINQ to SQL query, it is vital to
connect to the data source via DataContext class.
Insert, Update and Delete using LINQ To SQL
Add OR Insert
C#
using System;
using System.Linq;
namespace LINQtoSQL {
class LinqToSQLCRUD {
static void Main(string[] args) {
string connectString =
System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectio
nString"].ToString();
LinqToSQLDataContext db = new LinqToSQLDataContext(connectString);
//Create new Employee
Employee newEmployee = new Employee();
newEmployee.Name = "Michael";
newEmployee.Email = "yourname@companyname.com";
newEmployee.ContactNo = "343434343";
newEmployee.DepartmentId = 3;
newEmployee.Address = "Michael - USA";
//Add new Employee to database

db.Employees.InsertOnSubmit(newEmployee);
//Save changes to Database.
db.SubmitChanges();
//Get new Inserted Employee
Employee insertedEmployee = db.Employees.FirstOrDefault(e
⇒e.Name.Equals("Michael"));
Console.WriteLine("Employee Id = {0} , Name = {1}, Email = {2}, ContactNo = {3},
Address = {4}",
insertedEmployee.EmployeeId, insertedEmployee.Name, insertedEmployee.Email,
insertedEmployee.ContactNo, insertedEmployee.Address);
Console.WriteLine("nPress any key to continue.");
Console.ReadKey();
}
}
}
When the above code of C# is compiled and run, it produces the following
result −
Emplyee ID = 4, Name = Michael, Email = yourname@companyname.com, ContactNo =
343434343, Address = Michael - USA

Linq in C#

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