• About LINQ


    LINQ expression

    The Linq important part of Linq is about getting sequences from data sources. By default, the data sources that can be requested by Linq are:

    Object (Linq to Objetcs)
    XML fragments or docs (Linq to XML)
    ADO.Net DataSet (Linq to DataSet)
    SQL Server (Linq to SQL)
    Entity Framework (Linq to Entities

    LINQ is a unified programming model for any kind of data.

    var result = from s in stringList
                 where s.Contains("Tutorials")
                 select s;

    result = result variable
    s = Now property of stringList  transfer in s (range variable)
    strList = Sequence | Queryable collection
    Contains = Conditional Expression
    Where and Select = Standard Query Operators             

    • From s in student select  s.studentid, s.studentname;

    • From s in student select  s.studentid == 10;

    Q) Display all the students whose roll no is 15

    In SQL - Select * From Where

    In LINQ - From s in student select Rollno = 15;

    Simple Where clause

    var query_where1 = from a in AccountSet
            where a.Name.Contains("Atul")
            select a;

    Multiple Select and where operator

    Example: Multiple Select and where Operator

    var studentNames = studentList.Where(s => s.Age > 18)
                                  .Select(s => s)
                                  .Where(st => st.StandardID > 0)
                                  .Select(s => s.StudentName);

    Example: LINQ Query returns Collection of Anonymous Objects

    var teenStudentsName = from s in studentList
                           where s.age > 12 && s.age < 20
                           select new { StudentName = s.StudentName };



    Q) List out the three main components of LINQ? Explain what is the extension of the file, when LINQ to SQL is used?

    Three main components of LINQ are

        Standard Query Operators
        Language Extensions
        LINQ Providers

    The extension of the file used is .dbml

    Q) What are the types of LINQ?

        LINQ to Objects
        LINQ to XML
        LINQ to Dataset
        LINQ to SQL
        LINQ to Entities

    Q) What are Anonymous Types?

    Anonymous types are types that are generated by compiler at run time. When we create a anonymous type we do not specify a name. We just write properties names and their values. Compiler at runtime create these properties and assign values to them.

    var k = new { FirstProperty = "value1", SecondProperty = "value2" };

    Q) What is Anonymous function?

    An Anonymous function is a special function which does not have any name. We just define their parameters and define the code into the curly braces.

    Q) Define what is let clause?

    In a query expression, it is sometimes useful to store the result of a sub-expression in order to use it in subsequent clauses. You can do this with the let keyword, which creates a new range variable and initializes it with the result of the expression you supply.

    LinQ Operators

    Filtering Operators - Where
                     - OfType

    Filtering is an operation to restrict the result set such that it has only selected elements satisfying a particular condition.


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