LINQ

What is LINQ?

Basically LINQ address the current database development model in the context of Object Oriented Programming Model. If someone wants to develop database application on .Net platform the very simple approach he uses ADO.Net. ADO.Net is serving as middle ware in application and provides complete object oriented wrapper around the database SQL. Developing application in C# and VB.Net so developer must have good knowledge of object oriented concept as well as SQL, so it means developer must be familiar with both technologies to develop an application. If here I can say SQL statements are become part of the C# and VB.Net code so it’s not mistaken in form of LINQ. According to Anders Hejlsberg the chief architect of C#.

             “Microsoft original motivation behind LINQ was to address the impedance mismatch between programming languages and database.”

LINQ has a great power of querying on any source of data, data source could be the collections of objects, database or XML files. We can easily retrieve data from any object that implements the IEnumerable<T> interface. Microsoft basically divides LINQ into three areas and that are give below.

• LINQ to Object {Queries performed against the in-memory data}
• LINQ to ADO.Net
• LINQ to SQL (formerly DLinq) {Queries performed against the relation database only Microsoft SQL Server Supported}
• LINQ to DataSet {Supports queries by using ADO.NET data sets and data tables}
• LINQ to Entities {Microsoft ORM solution}
• LINQ to XML (formerly XLinq) { Queries performed against the XML source}

I hope few above lines increase your concrete knowledge about Microsoft LINQ and now we write some code snippet of LINQ.

1. Code Snippet

int[] nums = new int[] {0,1,2}; var res = from a in nums              where a < 3              orderby a              select a; foreach(int i in res)     Console.WriteLine(i); Output: 0 1 2

All SQL Operates are available in LINQ to Object like Sum Operator in the following code.

2. Code Snippet

int[] nums = new int[] {2,4,6,2}; int result = nums.Sum(); Console.WriteLine(result); Output: 1 2

One thing that I want to share with you guys is LINQ to Object support querying against any object that inherits from IEnumerable (all .Net collection inherits from IEnumerable interface). LINQ to Object provided main types of Operator Type that are give below.

Operator Types	Operator Name
Aggregation	Aggregate Average Count LongCount, Max, Min, Sum
Conversion	Cast, OfType, ToArray, ToDictionary, ToList, ToLookup, ToSequence
Element	DefaultIfEmpty, ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault
Equality	EqualAll
Generation	Empty, Range, Repeat
Grouping	GroupBy
Joining	GroupJoin, Join
Ordering	OrderBy, ThenBy, OrderByDescending, ThenByDescending, Reverse
Partitioning	Skip, SkipWhile,  Take,  TakeWhile
Quantifiers	All, Any, Contains
Restriction	Where
Selection	Select, SelectMany
Set	Concat, Distinct, Except, Intersect, Union

To the good use of above operator types I need samle patient class so here it

using System; public class Patient {     // Fields     private string _name;     private int _age;     private string _gender;     private string _area;     // Properties     public string PatientName     {         get { return _name; }         set { _name = value; }     }     public string Area     {         get { return _area; }         set { _area = value; }     }     public String Gender     {         get { return _gender; }         set { _gender = value; }     }     public int Age     {         get { return _age; }         set { _age = value; }     } }

Here is my code that intiliaze patients object with following data.

List<Patient> patients = new List<Patient> {            new Patient { PatientName="Ali Khan", Age=20, Gender="Male" , Area = "Gulshan"},            new Patient { PatientName="Ahmed Siddiqui", Age=25 ,Gender="Male", Area = "NorthKarachi" },            new Patient { PatientName="Nida Ali", Age=20, Gender="Female", Area = "NorthNazimabad"},            new Patient { PatientName="Sana Khan", Age=18, Gender="Female", Area = "NorthNazimabad"},            new Patient { PatientName="Shahbaz Khan", Age=19, Gender="Male", Area = "Gulshan"},            new Patient { PatientName="Noman Altaf", Age=19, Gender="Male", Area = "Gulshan"},            new Patient { PatientName="Uzma Shah", Age=23, Gender="Female", Area = "NorthKarachi"}}; Patient p = new Patient();         p.Age =33; p.Gender = "male";         p.PatientName = "Hammad Ali";          p.Area = "Defence";                  patients.Add(p);

This code snippet fetch those records whose gender is equal to “Male”. 

gdView.DataSource = from pa in patients                         where pa.Gender == "Male"                         orderby pa.PatientName, pa.Gender, pa.Age                         select pa;    gdView.DataBind();

The following code snippet uses the selection operator type, which brings all those records whose age is more than 20 years.

var mypatient = from pa in patients                   where pa.Age > 20                   orderby pa.PatientName, pa.Gender, pa.Age                   select pa;                 foreach(var pp in mypatient)         {         Debug.WriteLine(pp.PatientName + " "+ pp.Age + " " +          pp.Gender);         }

 The following code snippet uses the grouping operator type that group patient data on the bases area. 

var op = from pa in patients group pa by pa.Area into g select new {area = g.Key, count = g.Count(), allpatient = g};  foreach(var g in op)  {     Debug.WriteLine(g.count+ "," + g.area);     foreach(var l in g.allpatient)      {        Debug.WriteLine("\t"+l.PatientName);      }  }

This code snippet determine the count of those records, which lay in above 20 years. 

int patientCount = (from pa in patients                     where pa.Age > 20                     orderby pa.PatientName, pa.Gender, pa.Age                     select pa).Count();

All the above codes are few example of LINQ to Object technique of LINQ.