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Avoid Duplicate Entries In Database On Refreshing The Screen In Asp.Net

In this article I will explain how to avoid duplicate entries in database on refreshing the screen in asp.net.

Software Requirement

Before you start reading this tutorial you should make sure that Visual studio (any version) is installed on your machine.

Prerequisite Knowledge

Before you go ahead, it is required that you should know

Basics about ado.net.
Basics about SQL server.
How to create a project using visual studio?
What are page events like load, prerender etc.
Basics about asp.net controls and their events.
Basics about state objects like session, viewstate etc.

Steps Of Execution

In this tutorial I will execute certain steps for the demonstration of avoiding duplicate entries on refreshing the screen in asp.net. These steps are

Create a new project
Create a new table
Add button on the page
Add code to avoid duplicate entries in database on refreshing the screen

Let us execute each step

Create A New Project

Create a new website (Web based project). See the screen shot below

Picture showing the project structure of the web application in solution explorer

Click to Enlarge

Create A New Table

Create a new table Employee. See the screen shot below for table schema

Picture showing the table schema of the Employee table

Click to Enlarge

Add Button On The Page

Add a button on the screen. The purpose of this button is to insert data in the table.

Picture showing a web page with a button to insert a value in the Employee table

Click to Enlarge

Add Code To Avoid Duplicate Entries In Database On Refreshing The Screen

Add following code in code behind

protected void Page_Load(object sender, EventArgs e) {
	if (!IsPostBack) {
		Session["update"] = "N";
	}
}
protected void Button1_Click(object sender, EventArgs e) {
	if (Convert.ToString(ViewState["update"]) == Convert.ToString(Session["update"])) {
		string connectionstring = @"connection_string";
		using(SqlConnection connection = new SqlConnection(connectionstring)) {
			connection.Open();
			string query = string.Format("insert into Employee values('{0}','{1}')", "abc@abc.com", "test name");
			using(SqlCommand command = new SqlCommand(query, connection)) {
				command.ExecuteNonQuery();
				Session["update"] = "Y";
			}
		}
	}
}

protected void Page_PreRender(object sender, EventArgs e) {
	ViewState["update"] = Session["update"];
}

Code Explanation

In the code we have 3 events

Page load
Button click event
Page pre render

In page load event we are assigning ‘N’ to a session variable. It means that the value has not yet inserted into the database on button click.

On button click event we are checking if the value in session variable is equal to the value in view state. If both the values are same then execute the code of inserting data.

Initially when the page is loaded for the first time value in both and session contains ‘N’. So when the user clicks on button code for inserting data will execute and sets the session variable as ‘Y’. If the user clicks on refresh (or press F5) then even if the button click fires again the condition (checking values of session and view state) fails and data will not be inserted again.

On page pre render we are assigning the value in session to view state.

Output

Picture showing the table rows in the Employee table

Click to Enlarge

Posted By -	Karan Gupta

Posted On -	Wednesday, March 13, 2013

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