What is LINQ?

  • Microsoft Babies
    Microsoft new baby yes I am talking about LINQ stand for Language-Integrated Query is now available as a integral part of Visual Studio Orcas. Microsoft releases the new Visual Studio with the name of Orcas and all Microsoft previous efforts (Windows Communication Foundation WCF, Windows Workflow Foundation WWF, Windows Presentation Foundation WPF, Windows CardSpace and LINQ) are integrated in this Studio. From last one and half years Anders Hejlsberg team done a tremendous job in the overcoming the gap between the data impedance. Mr. Anders team gives a native syntax to developers in the form LINQ to C# and VB.Net for accessing data from any repository. The repository could be in memory object, database (still MS SQL Server only) and XML files.

    What is LINQ?
    Still lots of folks don’t understand what LINQ is doing. Basically LINQ address the current database development model in the context of Object Oriented Programming Model. If some one 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 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.
    Code Snippet
    int[] nums = new int[] {0,1,2};
    var res = from a in nums
    where a < nums =" int[]" result =" nums.Sum();">Aggregation
  • Aggregate , Average ,Count ,LongCount, Max, Min, Sum
  • Cast,OfType,ToArray,ToDictionary, ToList, ToLookup, ToSequence
  • DefaultIfEmpty, ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault
  • EqualAll
  • Empty, Range, Repeat
  • GroupBy
  • GroupJoin, Join
  • OrderBy, ThenBy, OrderByDescending, ThenByDescending, Reverse
  • Skip, SkipWhile, Take, TakeWhile
  • All, Any, Contains
  • Where
  • Select, SelectMany
  • 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 patients = new List {
    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";

    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;

    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 gselect 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)
    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. In my up coming post you will see both LINQ to SQL and LINQ to XML code snippets.

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