Differences between different datatypes in SQL Server

Differences between varchar and nvarchar in SQL Server

VARCHAR is an abbreviation for variable-length character string. It's a string of text characters that can be as large as the page size for the database table holding the column in question. The size for a table page is 8,196 bytes, and no one row in a table can be more than 8,060 characters. This in turn limits the maximum size of a VARCHAR to 8,000 bytes.

The "N" in NVARCHAR means uNicode. Essentially, NVARCHAR is nothing more than a VARCHAR that supports two-byte characters. The most common use for this sort of thing is to store character data that is a mixture of English and non-English symbols — in my case, English and Japanese.


Differences between char and varchar in SQL Server
char is used for fixed length memory storage whereas varchar is used for variable lenght memory storage.
Fox Example if we have char(10) then we can store 10 bit value in it but if we store only 6 bit value in it then rest of the 4 bit space is goes wasted. this limitation is overcome by varchar.
In varchar if we use less space than define space the rest of space is not wasted.

Differences between nchar and nvarchar in SQL Server

NCHAR and NVARCHAR data types are both Unicode character data types with a maximum length of 4,000 characters. The main difference between these 2 data types is that an NCHAR data type is fixed-length while an NVARCHAR is variable-length. If the number of characters entered in an NCHAR data type column is less than the specified column length, spaces are appended to it to fill up the whole length.

Another difference is in the storage size wherein the storage size for NCHAR is two times n bytes while for NVARCHAR is two times the number of characters entered (in bytes).

Differences between varchar and nvarchar in SQL Server 

VARCHAR and NVARCHAR data types are both character data types that are variable-length. Below is the summary of the differences between these 2 data types:

VARCHAR Character Data Type:- Non-Unicode Data
NVARCHAR Character Data Type:- Unicode Data

VARCHAR Maximum Length:- 8,000
NVARCHAR Maximum Length:- 4,000

VARCHAR Character Size:- 1 byte
NVARCHAR Character Size:- 2 byte

VARCHAR Storage Size:- Actual Length (in bytes)
NVARCHAR Storage Size:- 2 times Actual Length (in bytes)

You would use NVARCHAR data type for columns that store characters from more than one character set or when you will be using characters that require 2-byte characters, which are basically the Unicode characters such as the Japanese Kanji or Korean Hangul characters.

Disadvantages of LINQ over Stored procedures

Disadvantages of LINQ over stored procedures:

• LINQ needs to process the complete query, which might have a performance impact in case of complex queries against stored procedures which only need serialize sproc-name and argument data over the network.
• LINQ is generic, whereas stored procedures etc can take full advantage of the complete database features.
• If there has been a change, the assembly needs to be recompiled and redeployed whereas stored procedures are much simpler to update.
• It’s much easier to restrict access to tables in database using stored procedures and ACL’s than through LINQ.

Concept of Early Binding and Late Bindind in C#

Before discussing about the differences, let's know what is meant by Early and Late Binding.

Early Binding:
The name itself describes that compiler knows about what kind of object it is, what are all the methods and properties it contains. As soon as you declared the object, .NET Intellisense will populate its methods and properties on click of the dot button.

 

Common Examples:

 

ComboBox cboItems;
ListBox lstItems;

 

In the above examples, if we type the cboItem and place a dot followed by, it will automatically populate all the methods, events and properties of a combo box, because compiler already know it's an combobox.

 

Late Binding:
The name itself describes that compiler does not know what kind of object it is, what are all the methods and properties it contains. You have to declare it as an object, later you need get the type of the object, methods that are stored in it. Everything will be known at the run time.

 

Common Examples:

 

Object objItems;
objItems = CreateObject("DLL or Assembly name");

 

Here during the compile time, type of objItems is not determined. We are creating an object of a dll and assigning it to the objItems, so everything is determined at the run time.

 

Early Binding vs. Late Binding

• Application will run faster in Early binding, since no boxing or unboxing are done here.
• Easier to write the code in Early binding, since the intellisense will be automatically populated
• Minimal Errors in Early binding, since the syntax is checked during the compile time itself.
• Late binding would support in all kind of versions, since everything is decided at the run time.
• Minimal Impact of code in future enhancements, if Late Binding is used. 

Performance will be code in early binding.

Both have merits and demerits, it's the developer decision to choose the appropriate binding based on the scenario.

 

Getting the Index of a dataGridView Row in the MouseMove Event Window Application

private void dataGridView1_CellMouseMove(object sender, DataGridViewCellMouseEventArgs e)
  {
            if (e.RowIndex >= 0)
            {
                if (!((DataGridViewRow)(dataGridView1.Rows[e.RowIndex])).Selected)
                {
                    dataGridView1.ClearSelection();
                    ((DataGridViewRow)dataGridView1.Rows[e.RowIndex]).Selected = true;
                    if (dataGridView1.SelectedRows.Count > 0)
                    {
                       DataGridViewRow row = (DataGridViewRow)dataGridView1.Rows[e.RowIndex];
                        TextBox1.Text = e.RowIndex.ToString();
// return row index of dataGridView On CellMouseMove Event and Display RowIndex in TextBox1.                    }
                }
            }
        }

Sending Email using C# and ASP.Net

Most often, we will have requirements to send email from our asp.net applications. This article will help us understand some of the available techniques we can use to send email from asp.net applications. With the introduction of .Netframework 2.0, the classes for sending email are packed in System.Net.Mail namespace as opposed to System.Web.Mail namespace in 1.x framework. Moving forward we will see,

Ø       Sending a Simple Mail

Ø       Sending Mail with Attachment

Ø       Sending Mail with HTML body

Ø       Sending Email with Embedded Image in the Message Body

Ø       Sending Email with Gmail SMTP Server from ASP.Net

Sending a Simple Mail

MailMessage mail = new MailMessage();

mail.To.Add("to@gmail.com");

mail.From = new MailAddress("from@gmail.com");

mail.Subject = "Test Email";

string Body = "Welcome to Mysite.Com!!";

mail.Body = Body;

SmtpClient smtp = new SmtpClient();

smtp.Host = "smtp.gmail.com" ;

smtp.Send(mail);

Sending Mail with Attachment

We can also send email with attachments. The below code will help you to achieve it.

MailMessage mail = new MailMessage();

mail.To.Add("to@gmail.com");

mail.From = new MailAddress("From@gmail.com");

mail.Subject = "Test Email";

string Body = "Welcome to Mysite.Com!!";

mail.Body = Body;

mail.Attachments.Add(new Attachment(@"F:\Articles\Email in ASP.Net 2.0\SendEmail\mail.png"));

SmtpClient smtp = new SmtpClient();

smtp.Host = "smtp.gmail.com" ;

smtp.Send(mail);

Sending Mail with HTML Body

Sometimes, we will have requirements to send email as a HTML body. The below code will help you to achieve the same.

MailMessage mail = new MailMessage();

mail.To.Add("to@gmail.com");

mail.From = new MailAddress("From@gmail.com");

mail.Subject = "Test Email";

string Body = "Welcome to Mysite.com!!";

mail.Body = Body;

mail.IsBodyHtml = true;

SmtpClient smtp = new SmtpClient();

smtp.Host ="smtp.gmail.com" ;

smtp.Send(mail);

Sending Email with Gmail SMTP Server from ASP.Net

To send email using gmail SMTP server you will require a valid gmail userid and password. If you didn’t specify a valid gmail userid and password then you will get the following error.

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

The below code can be used to send email using gmail SMTP server, smtp.gmail.com.

MailMessage mail = new MailMessage();

mail.To.Add("to@gmail.com");

mail.From = new MailAddress("from@gmail.com");

mail.Subject = "Test Email";

string Body = "Welcome to Mysite.com!!";

mail.Body = Body;

mail.IsBodyHtml = true;

SmtpClient smtp = new SmtpClient();

smtp.Host ="smtp.gmail.com" ;

smtp.Credentials = new System.Net.NetworkCredential("mail@gmail.com","password");

smtp.EnableSsl = true;   

smtp.Send(mail);

Store Procedure

In this article, we will examine what a stored procedure is and how to call one from SQL Server database

.

Outline:

• Why Use Stored Procedures?
• Creating a Stored Procedure
• Calling a Stored Procedure
• Specifying Parameters
• Data Retrieval
• Inserting Data Using Parameters

Why Use Stored Procedures?

There are several advantages of using stored procedures instead of standard SQL. First, stored procedures allow a lot more flexibility offering capabilities such as conditional logic. Second, because stored procedures are stored within the DBMS, bandwidth and execution time are reduced. This is because a single stored procedure can execute a complex set of SQL statements. Third, SQL Server pre-compiles stored procedures such that they execute optimally. Fourth, client developers are abstracted from complex designs. They would simply need to know the stored procedure's name and the type of data it returns.

Creating a Stored Procedure

Enterprise Manager provides an easy way to create stored procedures. First, select the database to create the stored procedure on. Expand the database node, right-click on "Stored Procedures" and select "New Stored Procedure...". You should see the following:

CREATE PROCEDURE [OWNER].[PROCEDURE NAME] AS

Substitute OWNER with "dbo" (database owner) and PROCEDURE NAME with the name of the procedure. For example:

CREATE PROCEDURE [dbo].[GetProducts] AS

So far, we are telling SQL Server to create a new stored procedure with the name GetProducts. We specify the body of the procedure after the AS clause:

CREATE PROCEDURE [dbo].[GetProducts] AS
SELECT ProductID, ProductName FROM Products

Click on the Check Syntax button in order to confirm that the stored procedure is syntactically correct. Please note that the GetProducts example above will work on the Northwind sample database that comes with SQL Server. Modify it as necessary to suite the database you are using.

Now that we have created a stored procedure, we will examine how to call it from within a C# application.

Calling a Stored Procedure

A very nice aspect of ADO.NET is that it allows the developer to call a stored procedure in almost the exact same way as a standard SQL statement.

1. Create a new C# Windows Application project.

2. From the Toolbox, drag and drop a DataGrid onto the Form. Resize it as necessary.

3. Double-click on the Form to generate the Form_Load event handler. Before entering any code, add "using System.Data.SqlClient" at the top of the file.

Enter the following code:

private void Form1_Load(object sender, System.EventArgs e)
{
    SqlConnection conn = new SqlConnection("Data 
Source=localhost;Database=Northwind;Integrated Security=SSPI");
    SqlCommand command = new SqlCommand("GetProducts", conn);
    SqlDataAdapter adapter = new SqlDataAdapter(command);
    DataSet ds = new DataSet();
    adapter.Fill(ds, "Products");
    this.dataGrid1.DataSource = ds;
    this.dataGrid1.DataMember = "Products";
}

As you can see, calling a stored procedure in this example is exactly like how you would use SQL statements, only that instead of specifying the SQL statement, you specify the name of the stored procedure. Aside from that, you can treat it exactly the same as you would an ordinary SQL statement call with all the advantages of a stored procedure.

Specifying Parameters

Most of the time, especially when using non-queries, values must be supplied to the stored procedure at runtime. For instance, a @CategoryID parameter can be added to our GetProducts procedure in order to specify to retrieve only products of a certain category. In SQL Server, parameters are specified after the procedure name and before the AS clause.

CREATE PROCEDURE [dbo].[GetProducts] (@CategoryID int) AS
SELECT ProductID, ProductName FROM Products WHERE CategoryID = @CategoryID

Parameters are enclosed within parenthesis with the parameter name first followed by the data type. If more than one parameter is accepted, they are separated by commas:

CREATE PROCEDURE [dbo].[SomeProcedure] (
    @Param1 int,
    @Param2 varchar(50),
    @Param3 varchar(50)
) AS
...

For our GetProducts example, if @CategoryID was supplied with the value 1, the query would equate to:

SELECT ProductID, ProductName FROM Products WHERE CategoryID = 1

Which would select all the products that belong to CategoryID 1 or the Beverages category. To call the stored procedure, use Query Analyzer to execute:

exec GetProducts X

where X is the @CategoryID parameter passed to the stored procedure. To call the stored procedure from within a C# application using 1 as the @CategoryID parameter value, use the following code:

SqlConnection conn = new SqlConnection("Data 
Source=localhost;Database=Northwind;Integrated Security=SSPI");
SqlCommand command = new SqlCommand("GetProducts", conn);
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add("@CategoryID", SqlDbType.Int).Value = 1;
SqlDataAdapter adapter = new SqlDataAdapter(command);
DataSet ds = new DataSet();
adapter.Fill(ds, "Products");
this.dataGrid1.DataSource = ds;
this.dataGrid1.DataMember = "Products";

Note that you must now specify the CommandType property of the SqlCommand object. The reason we did not do this in the first example was that it is not required if the stored procedure does not accept parameters. Of course, specifying the CommandType property even if it is not needed may improve readability. The next line actually combines two lines in one:

command.Parameters.Add("@CategoryID", SqlDbType.Int);
command.Parameters["@CategoryID"].Value = 1;

The first line of this segment specifies that the command object (which calls the GetProducts stored procedure) accepts a parameter named @CategoryID which is of type SqlDbType.Int. The type must be the same as the data type specified by the stored procedure. The second line of this code segment gives the parameter the value 1. For simplicity, especially when using more than one parameter, I prefer to combine to two lines into a single line:

command.Parameters.Add("@CategoryID", SqlDbType.Int).Value = 1;

The rest of the code is the same as in the previous example without parameters. As illustrated in the previous examples, ADO.NET takes a lot of pain out of database programming. Calling a stored procedure uses virtually the same code as using standard SQL and specifying parameters is a painless process.

Data Retrieval

Data Retrieval with stored procedures is the same (surprise!) as if using standard SQL. You can wrap a DataAdapter around the Command object or you can use a DataReader to fetch the data one row at a time. The previous examples have already illustrated how to use a DataAdapter and fill a DataSet. The following example shows usage of the DataReader:

SqlConnection conn = new SqlConnection("Data 
Source=localhost;Database=Northwind;Integrated Security=SSPI");
SqlCommand command = new SqlCommand("GetProducts", conn);
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add("@CategoryID", SqlDbType.Int).Value = 1;
conn.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
    Console.WriteLine(reader["ProductName"]);
}
conn.Close();

Again, using either a DataAdapter or a DataReader against a query from a stored procedure is the same as specifying the SQL from within the code.

Inserting Data Using Parameters

Using other SQL statements such as INSERT, UPDATE or DELETE follow the same procedure. First, create a stored procedure that may or may not accept parameters, and then call the stored procedure from within the code supply the necessary values if parameters are needed. The following example illustrates how to insert a new user in a users table that has a username and password field.

CREATE PROCEDURE [dbo].[InsertUser] (
    @Username varchar(50),
    @Password varchar(50)
) AS
INSERT INTO Users VALUES(@Username, @Password)

string username = ... // get username from user
string password = ... // get password from user
SqlConnection conn = new SqlConnection("Data 
Source=localhost;Database=MyDB;Integrated Security=SSPI");
SqlCommand command = new SqlCommand("InsertUser", conn);
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add("@Username", SqlDbType.VarChar).Value = username;
command.Parameters.Add("@Password", SqlDbType.VarChar).Value = password;
conn.Open();
int rows = command.ExecuteNonQuery();
conn.Close();

First, we retrieve the username and password information from the user. This information may be entered onto a form, through a message dialog or through some other method. The point is, the user specifies the username and password and the applicaton inserts the data into the database. Also notice that we called the ExecuteNonQuery() method of the Connection object. We call this method to indicate that the stored procedure does not return results for a query but rather an integer indicating how many rows were affected by the executed statement. ExecuteNonQuery() is used for DML statements such as INSERT, UPDATE and DELETE. Note that we can test the value of rows to check if the stored procedure inserted the data successfully.

if (rows == 1)
{
    MessageBox.Show("Create new user SUCCESS!");
}
else
{
    MessageBox.Show("Create new user FAILED!");
}

We check the value of rows to see if it is equal to one. Since our stored procedure only did one insert operation and if it is successful, the ExecuteNonQuery() method should return 1 to indicate the one row that was inserted. For other SQL statements, especially UPDATE and DELETE statements that affect more than one row, the stored procedure will return the number of rows affected by the statement.

DELETE FROM Products WHERE ProductID > 50

This will delete all products whose product ID is greater than 50 and will return the number of rows deleted.

Conclusion

Stored procedures offer developers a lot of flexibility with many features not available using standard SQL. ADO.NET allows us to use stored procedures in our applications seamlessly. The combination of these two allows us to create very powerful appliations rapidly.

Passing Data Between Forms

Introduction

Some of you would have faced a scenario where you wanted to pass data from one form to another in WinForms. Honestly, I too had a similar problem (that’s why I am writing this article!).
There are so many methods (How many? I don't know) to pass data between forms in Windows application. In this article, let me take four important (easiest) ways of accomplishing this:

1. Using constructor
2. Using objects
3. Using properties
4. Using delegates

Let us see all the above methods in detail in the following sections.
For data to be passed between forms using any of the above methods, we need two forms and some controls. Let us start by following the steps given below.

Step 1

Create a new project and select Windows application. This will create a default form as “Form1”. We can use this form for sending data.

Step 2

Add a textbox and a button to the form.

Step 3

Add another Windows Form for receiving the data and to display it. Right click the project and select Add->Add Windows Form. Enter a name or use the default name “Form2.cs” and click ok button.

Step 4

Add a label to the second form to display the text from form1.

The Constructor Approach

This could be the easiest method of all. A method is invoked whenever you instantiate an object. This method is called a constructor. Code a constructor for form2 class with one string parameter. In the constructor, assign the text to the label’s text property. Instantiate form2 class in form1’s button click event handler using the constructor with one string parameter and pass the textbox’s text to the constructor.
Follow the steps given below:

Step 1

Code a constructor for form2 class as below:

public Form2(string strTextBox)
{
  InitializeComponent(); 
  label1.Text=strTextBox;
}

Step 2

Instantiate form2 class in form1’s button click event handler as below:

private void button1_Click(object sender, System.EventArgs e)
{
    Form2 frm=new Form2(textBox1.Text);
    frm.Show();
}

The Object Approach

Objects are reference types, and are created on the heap, using the keyword new. Here we are going to pass data using objects. The approach is simple; in form2 we are going to instantiate form1 class.
Then instantiate form2 in the button click event handler of form1. After this we are going to pass form1 object to the form2 using form2’s form1 object. The last step is to invoke the form2 window by calling the form2’s show method.
Follow the below steps:

Step 1

Change the access modifier for textbox in form1 to public:

public class Form1 : System.Windows.Forms.Form
{  
 public System.Windows.Forms.TextBox textBox1;

Step 2

In the button click event-handler, add the following code:

private void btnSend_Click(object sender, System.EventArgs e)
{
    Form2 frm= new Form2();
    frm.frm1=this;
    frm.Show();
}

Step 3

In form2.cs, instantiate form1 class:

public class Form2 : System.Windows.Forms.Form
{
     private System.Windows.Forms.Label label1;
     public Form1 frm1;

Step 4

In Form2’s Load method, type cast the object (frm1) of form1 to Form1 and access form1’s textbox and assign its text to label’s text.

private void Form2_Load(object sender, System.EventArgs e)
{
    label1.Text=((Form1)frm1).textBox1.Text;
}

The Properties Approach

Properties allow clients to access class state as if they were accessing member fields directly, while actually implementing that access through a class method. In this method, we are going to add one property to each form. In form1 we are going to use one property for retrieving value from the textbox and in form2, one property to set the label’s text property. Then, in form1’s button click event handler, we are going to instantiate form2 and use the form2’s property to set the label’s text.
Follow the below steps:

Step 1

Add a property in form1 to retrieve value from textbox:

public string _textBox1
{
    get{return textBox1.Text;}
}

Step 2

Add a property in form2 to set the labels’ text:

public string _textBox
{
   set{label1.Text=value;}
}

Step 3

In form1’s button click event handler, add the following code:

private void button1_Click(object sender, System.EventArgs e)
{
     Form2 frm=new Form2();
     frm._textBox=_textBox1;
     frm.Show();
}

The Delegates Approach

Technically, a delegate is a reference type used to encapsulate a method with a specific signature and return type. You can encapsulate any matching method in that delegate. Here we are going to create a delegate with some signature and assign a function to the delegate to assign the text from textbox to label.
Follow the below steps:

Step 1

Add a delegate signature to form1 as below:

public delegate void delPassData(TextBox text);

Step 2

In form1’s button click event handler, instantiate form2 class and delegate. Assign a function in form2 to the delegate and call the delegate as below:

private void btnSend_Click(object sender, System.EventArgs e)
{
    Form2 frm= new Form2();
    delPassData del=new delPassData(frm.funData);
    del(this.textBox1);
    frm.Show();
}

Step 3

In form2, add a function to which the delegate should point to. This function will assign textbox’s text to the label:

public void funData(TextBox txtForm1)
{
    label1.Text = txtForm1.Text;
}

C# to give download link in gridview control

Source code fot gridview:-

   1:  <asp:GridView ID="grdsearch" runat="server" AutoGenerateColumns="False">

   2:                             

   3:<Columns>

   4: <asp:BoundField HeaderText="Full Name" DataField="FullName"/>

   5: <asp:BoundField HeaderText="Email ID" DataField="Email"/>

   6: <asp:BoundField HeaderText="Gender" DataField="Sex"/>

   7: <asp:BoundField HeaderText="Education" DataField="Education"/>

   8: <asp:BoundField HeaderText="Skills" DataField="Skillsetdetails"/>

   9: <asp:BoundField HeaderText="Total Experience" DataField="Totalexperience"/>

  10: <asp:BoundField HeaderText="Relvent Experience" DataField="Relventexperience"/>

  11: <asp:BoundField HeaderText="Address" DataField="Address"/>

  12: <asp:BoundField HeaderText="Previous Company Detail" DataField="Previousemployerdetail"/>

  13: <asp:BoundField HeaderText="Mobile Number" DataField="Mobileno"/>

  14: <asp:BoundField HeaderText="Availability" DataField="Availability"/>

  15: <asp:BoundField HeaderText="Currentctc" DataField="Currentctc"/>

  16: <asp:BoundField HeaderText="Expectedctc" DataField="Expectedctc"/>

  17: <asp:BoundField HeaderText="Preferred Location" DataField="StateName"/>

  18: <asp:BoundField HeaderText="Resume Name" DataField="ResumeName"/>

  19: <asp:TemplateField>

  20:  <ItemTemplate>

  21: <asp:LinkButton ID="LinkButton1" runat="server" Text="Resume Download" 

    CommandArgument='<%#Eval("Attachment")%>' OnCommand="btnDownload_Click">

  22:   

  23: asp:LinkButton>

  24:     ItemTemplate>

  25: asp:TemplateField>

  26:                  

  27:  Columns>

  28:  asp:GridView>

C# code to make file download on linkbutton click:-

 protected void btnDownload_Click(object sender, System.Web.UI.WebControls.CommandEventArgs e)
        {
            //Response.Write(e.CommandArgument.ToString());
            //Response.Write(e.CommandName.ToString()  );

            string queryString = e.CommandArgument.ToString();
            Response.Redirect(queryString);

        }

Deleting Multiple Rows in a GridView

If you have used Hotmail or any other similar email client, you might have observed that  we have the option of selecting multiple rows (using the checkbox provided) and perform a set of operations on them. In this article, we will replicate this scenario for a gridview. A gridview allows us to delete only a single row at a time. We will extend this functionality to select multiple rows and delete all of the selected rows in a single stroke. In this article, I assume that you are aware of creating asp.net web applications and have worked with gridview.

The sample makes use of the Northwind database. We will be pulling data from the Employee table. For this sample to work, drop all the Foreign Key relationships on the Employee Table. To do so, in Sql Server Management Studio, browse to the Northwind database and open the Employee table in design view. Right click in the Table designer on the right hand side and choose ‘Relationships’. Select all the relationships like FK_Orders_Employees,  FK_EmployeeTerritories_Employees etc and delete them. This step is necessary as we will get a constraint violation exception if we do not do so.

Once we are through with the task of removing the relationships in the Employee table, let us explore the steps to create a gridview with functionality to delete multiple rows at a time.

Perform the following steps :

Step 1: Create an .aspx page and add a GridView and a SqlDataSource control to it.

Step 2: Configure the connection of SqlDataSource to point to the Northwind database.  Create queries for the Select and Delete commands. The resultant code will look similar as given below :

<asp:SqlDataSource ID="SqlDataSource1" Runat="server"

    SelectCommand="SELECT EmployeeID, LastName, City FROM Employees"

    DeleteCommand="DELETE FROM Employees WHERE [EmployeeID] = @EmployeeID"

    ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>" >

       <DeleteParameters>

           <asp:Parameter Name="EmployeeID" />

       DeleteParameters>

asp:SqlDataSource>                                   

Step 3: Once the SqlDataSource has been configured, bind the gridview with this data source.

Step 4: To create a checkbox in each row, follow these steps:

1.    Create a TemplateField inside the <Columns> to add custom content to each column.

2.    Inside the TemplateField, create an ItemTemplate with a CheckBox added to it.

<asp:TemplateField>

       <ItemTemplate>

             <asp:CheckBox ID="chkRows" runat="server"/>

      ItemTemplate>

 asp:TemplateField>

This will add a checkbox to each row in the grid.

Step 5: Add a button control, and rename it to btnMultipleRowDelete.

The resultant markup in the design view will look similar to the code below :

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="EmployeeID" DataSourceID="SqlDataSource1">

  

   <Columns>

      <asp:TemplateField>

          <ItemTemplate>

            <asp:CheckBox ID="cbRows" runat="server"/>

          ItemTemplate>

       asp:TemplateField>

 

<asp:BoundField DataField="EmployeeID" HeaderText="EmployeeID" InsertVisible="False" ReadOnly="True" SortExpression="EmployeeID" />

<asp:BoundField DataField="LastName" HeaderText="LastName" SortExpression="LastName" />

<asp:BoundField DataField="City" HeaderText="City" SortExpression="City" />

   Columns>

asp:GridView>

 

<asp:SqlDataSource ID="SqlDataSource1" Runat="server"

SelectCommand="SELECT EmployeeID, LastName, City FROM Employees"

DeleteCommand="DELETE FROM Employees WHERE [EmployeeID] = @EmployeeID"

ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>" >

   <DeleteParameters>

       <asp:Parameter Name="EmployeeID" />

   DeleteParameters>

asp:SqlDataSource>

 

<asp:Button

   ID="btnMultipleRowDelete"

   OnClick="btnMultipleRowDelete_Click"

   runat="server"

   Text="Delete Rows" />

 

In Code behind file (.cs) for C# and (.vb) for VB.NET, code the button click event. Our code will first loop through all the rows in the GridView. If a row is checked, the code retrieves the EmployeeID and passes the selected value to the Delete Command.

C#

 

 

protected void btnMultipleRowDelete_Click(object sender, EventArgs e)

{

        // Looping through all the rows in the GridView

        foreach (GridViewRow row in GridView1.Rows)

        {

            CheckBox checkbox = (CheckBox)row.FindControl("cbRows");

 

            //Check if the checkbox is checked.

//value in the HtmlInputCheckBox's Value property is set as the //value of the delete command's parameter.

            if (checkbox.Checked)

            {

                // Retreive the Employee ID

int employeeID = Convert.ToInt32(GridView1.DataKeys[row.RowIndex].Value);

// Pass the value of the selected Employye ID to the Delete //command.

SqlDataSource1.DeleteParameters["EmployeeID"].DefaultValue = employeeID.ToString();

                SqlDataSource1.Delete();

            }

        }

 }

How to show Print Dialog Box when a button is clicked(Window Application)

 private void button1_Click(object sender, EventArgs e)
{
        PrintDialog p = new PrintDialog(); 
                 p.ShowDialog();

}

Abstract Class versus Interface

Introduction

In this article along with the demo project I will discuss Interfaces versus Abstract classes. The concept of Abstract classes and Interfaces is a bit confusing for beginners of Object Oriented programming. Therefore, I am trying to discuss the theoretical aspects of both the concepts and compare their usage. And finally I will demonstrate how to use them with C#.

Background

An Abstract class without any implementation just looks like an Interface; however there are lot of differences than similarities between an Abstract class and an Interface. Let's explain both concepts and compare their similarities and differences.

What is an Abstract Class?

An abstract class is a special kind of class that cannot be instantiated. So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.

What is an Interface?

An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments. The main difference between them is that a class can implement more than one interface but can only inherit from one abstract class. Since C# doesn�t support multiple inheritance, interfaces are used to implement multiple inheritance.

Both Together

When we create an interface, we are basically creating a set of methods without any implementation that must be overridden by the implemented classes. The advantage is that it provides a way for a class to be a part of two classes: one from inheritance hierarchy and one from the interface.
When we create an abstract class, we are creating a base class that might have one or more completed methods but at least one or more methods are left uncompleted and declared abstract. If all the methods of an abstract class are uncompleted then it is same as an interface. The purpose of an abstract class is to provide a base class definition for how a set of derived classes will work and then allow the programmers to fill the implementation in the derived classes.
There are some similarities and differences between an interface and an abstract class that I have arranged in a table for easier comparison:

Feature	Interface	Abstract class
Multiple inheritance	A class may inherit several interfaces.	A class may inherit only one abstract class.
Default implementation	An interface cannot provide any code, just the signature.	An abstract class can provide complete, default code and/or just the details that have to be overridden.
Access Modfiers	An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public	An abstract class can contain access modifiers for the subs, functions, properties
Core VS Peripheral	Interfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface.	An abstract class defines the core identity of a class and there it is used for objects of the same type.
Homogeneity	If various implementations only share method signatures then it is better to use Interfaces.	If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.
Speed	Requires more time to find the actual method in the corresponding classes.	Fast
Adding functionality (Versioning)	If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method.	If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.
Fields and Constants	No fields can be defined in interfaces	An abstract class can have fields and constrants defined

Using the Code

Let me explain the code to make it a bit easier. There is an Employee abstract class and an IEmployee interface. Within the Abstract class and the Interface entity I am commenting on the differences between the artifacts.
I am testing both the Abstract class and the Interface by implementing objects from them. From the Employee abstract class, we have inherited one object: Emp_Fulltime. Similarly from IEmployee we have inherited one object: Emp_Fulltime2.
In the test code under the GUI, I am creating instances of both Emp_Fulltime and Emp_Fulltime2 and then setting their attributes and finally calling the calculateWage method of the objects.

Abstract Class Employee

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using System;

namespace AbstractsANDInterfaces
{
    /// 


    /// Summary description for Employee.

    /// 

    
    public abstract class Employee
    {
        //we can have fields and properties 


        //in the Abstract class

        protected String id;
        protected String lname;
        protected String fname;

        //properties


        public abstract String ID
        {
            get;
            set;
        }

        public abstract String FirstName
        {
            get;
            set;
        }
        
        public abstract String LastName
        {
            get;
            set;
        }
        //completed methods


        public String Update()
        {
            return "Employee " + id + " " + 
                      lname + " " + fname + 
                      " updated";
        }
        //completed methods


        public String Add()
        {
            return "Employee " + id + " " + 
                      lname + " " + fname + 
                      " added";
        }
        //completed methods


        public String Delete()
        {
            return "Employee " + id + " " + 
                      lname + " " + fname + 
                      " deleted";
        }
        //completed methods


        public String Search()
        {
            return "Employee " + id + " " + 
                      lname + " " + fname + 
                      " found";
        }

        //abstract method that is different 


        //from Fulltime and Contractor

        //therefore i keep it uncompleted and 

        //let each implementation 

        //complete it the way they calculate the wage.


        public abstract String CalculateWage();
        
    }
}

Interface Employee

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using System;


namespace AbstractsANDInterfaces
{
    /// <summary>


    /// Summary description for IEmployee.

    /// </summary>

    public interface IEmployee
    {
        //cannot have fields. uncommenting 


        //will raise error!
        //        protected String id;
        //        protected String lname;
        //        protected String fname;


        //just signature of the properties 

        //and methods.

        //setting a rule or contract to be 

        //followed by implementations.


        String ID
        {
            get;
            set;
        }

        String FirstName
        {
            get;
            set;
        }
        
        String LastName
        {
            get;
            set;
        }
        
        // cannot have implementation


        // cannot have modifiers public 

        // etc all are assumed public

        // cannot have virtual


        String Update();

        String Add();

        String Delete();

        String Search();

        String CalculateWage();
    }
}

Inherited Objects

Emp_Fulltime:

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using System;

namespace AbstractsANDInterfaces
{
    /// 


    /// Summary description for Emp_Fulltime.

    /// 

     
    //Inheriting from the Abstract class

    public class Emp_Fulltime : Employee
    {
        //uses all the properties of the 


        //Abstract class therefore no 

        //properties or fields here!


        public Emp_Fulltime()
        {
        }


        public override String ID
        {
            get

            {
                return id;
            }
            set
            {
                id = value;
            }
        }
        
        public override String FirstName
        {
            get

            {
                return fname;
            }
            set
            {
                fname = value;
            }
        }

        public override String LastName
        {
            get

            {
                return lname;
            }
            set
            {
                lname = value;
            }
        }

        //common methods that are 

        //implemented in the abstract class

        public new String Add()
        {
            return base.Add();
        }
        //common methods that are implemented 


        //in the abstract class

        public new String Delete()
        {
            return base.Delete();
        }
        //common methods that are implemented 


        //in the abstract class

        public new String Search()
        {
            return base.Search();
        }
        //common methods that are implemented 


        //in the abstract class

        public new String Update()
        {
            return base.Update();
        }
        
        //abstract method that is different 


        //from Fulltime and Contractor

        //therefore I override it here.

        public override String CalculateWage()
        {
            return "Full time employee " + 
                  base.fname + " is calculated " + 
                  "using the Abstract class...";
        }
    }
}

Emp_Fulltime2:

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using System;

namespace AbstractsANDInterfaces
{
    /// 

    /// Summary description for Emp_fulltime2.


    /// 

    
    //Implementing the interface

    public class Emp_fulltime2 : IEmployee
    {
        //All the properties and 


        //fields are defined here!

        protected String id;
        protected String lname;
        protected String fname;

        public Emp_fulltime2()
        {
            //


            // TODO: Add constructor logic here

            //

        }

        public String ID
        {
            get

            {
                return id;
            }
            set
            {
                id = value;
            }
        }
        
        public String FirstName
        {
            get
            {
                return fname;
            }
            set

            {
                fname = value;
            }
        }

        public String LastName
        {
            get
            {
                return lname;
            }
            set
            {
                lname = value;
            }
        }

        //all the manipulations including Add,Delete, 


        //Search, Update, Calculate are done

        //within the object as there are not 

        //implementation in the Interface entity.

        public String Add()
        {
            return "Fulltime Employee " + 
                          fname + " added.";
        }

        public String Delete()
        {
            return "Fulltime Employee " + 
                        fname + " deleted.";
        }

        public String Search()
        {
            return "Fulltime Employee " + 
                       fname + " searched.";
        }

        public String Update()
        {
            return "Fulltime Employee " + 
                        fname + " updated.";
        }
        
        //if you change to Calculatewage(). 


        //Just small 'w' it will raise 

        //error as in interface

        //it is CalculateWage() with capital 'W'.

        public String CalculateWage()
        {
            return "Full time employee " + 
                  fname + " caluculated using " + 
                  "Interface.";
        }
    }
}

Code for Testing

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//This is the sub that tests both 

//implementations using Interface and Abstract

private void InterfaceExample_Click(object sender, 
                                System.EventArgs e)
{
    try

    {

        IEmployee emp;

        Emp_fulltime2 emp1 = new Emp_fulltime2();

        emp =  emp1;
        emp.ID = "2234";
        emp.FirstName= "Rahman" ;
        emp.LastName = "Mahmoodi" ;
        //call add method od the object


        MessageBox.Show(emp.Add().ToString());
        
        //call the CalculateWage method

        MessageBox.Show(emp.CalculateWage().ToString());


    }
    catch(Exception ex)
    {
        MessageBox.Show(ex.Message);
    }

}

private void cmdAbstractExample_Click(object sender, 
                                   System.EventArgs e)
{

    Employee emp;

    emp = new Emp_Fulltime();
    

    emp.ID = "2244";
    emp.FirstName= "Maria" ;
    emp.LastName = "Robinlius" ;
    MessageBox.Show(emp.Add().ToString());

    //call the CalculateWage method


    MessageBox.Show(emp.CalculateWage().ToString());

}

Recommendations on using Abstract Classes and Interfaces
1. If you anticipate creating multiple versions of your component, create an
abstract class. Abstract classes provide a simple and easy way to
version your components. By updating the base class, all inheriting
classes are automatically updated with the change. Interfaces, on the
other hand, cannot be changed once created. If a new version of an
interface is required, you must create a whole new interface. 

2. If the functionality you are creating will be useful across a wide
range of disparate objects, use an interface. Abstract classes should
be used primarily for objects that are closely related, whereas
interfaces are best suited for providing common functionality to
unrelated classes. 

3. If you are designing small, concise bits of functionality, use interfaces.

If you are designing large functionalunits, use an abstract class. 

4. If you want to provide common,implemented functionality among all

implementations of your component,use an abstract class. 

Abstract classes allow you to partially implement your class,

whereas interfaces contain no implementation for any members.