First and Last Method in LINQ

Written By:-Isha Malhotra 
Our Website:-www.techaltum.com    

First and Last in LINQ

Use of First in LINQ

First method in LINQ just select the top 1 value from the data source.

For Example:-

First with array

int[] marks = new int[] { 23, 45, 78, 45, 56, 89, 56, 32 };

       int first = marks.First();

       Response.Write("First Element " + first);

Ouput

We can also pass condition while calling first method

Use of long count in LINQ

Written By:-Isha Malhotra 

Our Website:-www.techaltum.com

Use of long count in LINQ

Long count is similar to count as it works same but the only difference between them is that long count returns a 64 bit integer.

For Example:-

int[] marks = new int[] { 23, 45, 78, 90, 56, 89, 10, 32 };

      Int64 res = marks.LongCount(x => x % 2 == 0);

                        OR

long res_long = marks.LongCount(x => x % 2 == 0);

       Response.Write(res_long);

The output of this code will be 5.

LINQ Hour 5-3 Skip/SkipWhile and Take/TakeWhile in LINQ

Written By:-Isha Malhotra 

Our Website:-www.techaltum.com

Skip/SkipWhile and Take/TakeWhile

Skip

Skip in LINQ is used to skip values from the beginning. We pass a numeric value to skip which represent that how many values we need to skip.

For example

Skip with array

int[] marks = new int[] { 23, 45, 78, 90, 56, 89, 10, 32 };

        var data_skip = (from res_skip in marks

                         orderby res_skip

                         select res_skip).Skip(3);

        Response.Write("Result using skip and skip count is 3 <br/>");

        foreach (int res_data_skip in data_skip)

        {

       

            Response.Write(res_data_skip+" ");

       

        }

Output

Figure 1

It simple arrange in ascending order and then skip 3 records as we gave 3 as input in the skip.

LINQ Hour 5-2 Sorting in LINQ

Written By:-Isha Malhotra 

Our Website:-www.techaltum.com

Sorting in LINQ

To sort data in LINQ we use orderby in the following manner:-

Sorting with Array

int[] marks = new int[] { 23, 45, 78, 90, 56, 89, 10, 32 };

        // it will sort in ascending order

        var sort_asc = from res_asc in marks

                       orderby res_asc

                       select res_asc;

        //it will sort in descending order

        var sort_desc = from res_desc in marks

                        orderby res_desc descending

                        select res_desc;

        Response.Write("Ascending order result <br/>");

        foreach (int res_asc in sort_asc)

        {

            Response.Write(res_asc + " ");

       

        }

        Response.Write("<br/>descending order result <br/>");

        foreach (int res_desc in sort_desc)

        {

            Response.Write(res_desc + " ");

        }

The output of the code is as follows:-

Figure 1

LINQ Hour 5 -1 Aggregate function in LINQ

Written By:-Isha Malhotra 

Our Website:-www.techaltum.com

Aggregate function using LINQ

We use many aggregate functions like sum, count, average, min, and max. In LINQ we can use this function in the following manner:-

SUM

If we want to perform sum aggregate function then we will implement the following queries:-

Sum with array

int[] marks = new int[] { 23, 45, 78, 90, 56, 89, 10, 32 };

        //simple sum without condition

        int res = marks.Sum();

        //sum with condition

        int res_with_where = marks.Where(cond => cond > 50).Sum();

      

        Response.Write("Sum without condition= " + res + "<br/>");

        Response.Write("Sum with condition="+ res_with_where+"<br/>");

Output of this code as follows:-

Figure 1

LINQ Hour 5 - Queries using LINQ

Written By:-Isha Malhotra 

Our Website:-www.techaltum.com

Perform different functionality (QUERY) using LINQ

As in the previous article I already discussed about select, insert, update and delete. I also discussed with where clause, order by, grouping. In this hour I will discuss about different operation which we can perform using LINQ. As we know we can perform this functionality on array, generics, database, xml etc. so here I am taking the example of array, generics and database. I will discuss xml separately.  

To work with this functionality I am taking the following source:-

Array

Using following int array:-

int[] marks = new int[] { 23, 45, 78, 90, 56, 89, 10, 32 };

Generics:-

Using following class to implement generics:-

public class data

{

    public int roll_no;

    public string student;

    public int per;

}

And following list:-

List<data> dt = new List<data>()

        {

            new data{roll_no=1, student="isha", per=100},

            new data{roll_no=2, student="neha", per=89},

            new data{roll_no=3, student="rahul", per=34}

        };

Database

Using following table:-

Figure 1

And create its class to mapping this table which is as follows:-

[Table(Name="prod_rep")]

public class Class1

{

   

    [Column]

    public int id;

    [Column]

    public int prod_year;

    [Column]

    public string dept;

    [Column]

    public int no_of_prod;

}

click on the following link to perform different functionality:-

Part 1 Aggregate function in LINQ

Part 2 Sorting in LINQ

Part 3 Take / TakeWhile and Skip / SkipWhile

LINQ- Hour 3 (LINQ to XML)

LINQ to XML

When we interact with XML using LINQ then it is known as LINQ to XML.

To work with XML in LINQ you have to add a namespace

using System.Xml.Linq.

I am taking the following xml file for an example:-

<?xml version=”1.0” encoding=”utf-8” ?>

<Techaltum>

<student Code=”101”>

        <name>isha malhotra</name>

        <id> 1 </id>

        <course> asp.net </course>

    </student>

<student Code=”102”>

        <name>Avi malhotra</name>

        <id> 2 </id>

        <course> Web Designing </course>

    </student>

<student Code=”103”>

        <name>Neha</name>

        <id> 3 </id>

        <course> Java </course>

    </student>

</Techaltum>

If I consider this xml file then in this file first line is declaration. Techaltum is an element and in student element code is attribute.

First I will discuss how to declare all these in LINQ.

Syntax of Declaration in LINQ:-

XDeclaration dec = new XDeclaration("1.0", "utf-8", "yes");