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Datakeynames Attribute In .Net

In this tutorial I will explain about DataKeyNames attribute.

Software Requirement

Before you start reading this tutorial you should make sure that visual studio 2005(or above versions) is installed on your machine.

Prerequisite Knowledge

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

What is a gridview control?
How to bind data to a gridview control?
How RowDataBound event in a gridview works?

Problem : Get The Value Of Primary Key Column In Gridview Control

Consider a gridview control which contains the information of the employees

Picture showing the gridview control with data bound with it

Click to Enlarge

The .net code for this gridview is

<asp:GridView ID="gvXMLBind" runat="server" AutoGenerateColumns="false" OnRowDataBound="gvXMLBind_RowDataBound">
	<Columns>
		<asp:BoundField DataField="ID" HeaderText="Employee ID" />
		<asp:BoundField DataField="name" HeaderText="Employee Name" /> 
   </Columns>
</asp:GridView>

To hide the primary key column (ID) you have to write RowDataBound event

protected void gvXMLBind_RowDataBound(object sender, GridViewRowEventArgs e) {
  e.Row.Cells[0].Visible = false;
}

and to get the value of this column you have to use e.Row.Cells[0].Text.

Readers should note that you cannot hide the column by setting the visible attribute to false, because when the attribute is set at compile time the column is not rendered as HTML and you will not get the value of column at run time.

Problem With The Approach

This approach creates a problem when the sequence of fields will change. At that time e.Row.Cells[0] will point to some column and the functionality of your page will not work as per the requirement.

Solution : Datakeynames Attribute

DataKeyNames is an array that contains the names of fields for the items displayed in the data controls like gridview.

Syntax

<asp:GridView runat="server" ID="<gridview_ID>" DataKeyNames="<list_of_field_names_separated_by_comma>"></asp:GridView>

Description Of Datakeynames Attribute

When field name(or multiple field names separated by comma) is specified then names are stored in an array. For example if we specify the attribute value as column_name_one, column_name_two.Then the value in array is stored as

Picture showing how the datakeynames property is applied to the columns separated by comma

Click to Enlarge

Resolution Using Datakeynames Attribute

A better approach is to set the value of DataKeyNames attribute to the column name. So the gridview code is changed to

<asp:GridView ID="gvXMLBind" runat="server" AutoGenerateColumns="false" OnRowDataBound="gvXMLBind_RowDataBound" DataKeyNames="ID">
	<Columns>
		<asp:BoundField DataField="ID" HeaderText="Employee ID" />
		<asp:BoundField DataField="name" HeaderText="Employee Name" /> 
   </Columns>
</asp:GridView>

Now we can set the visibility of column at compile time. The column value is fetched using the following code

protected void gvXMLBind_RowDataBound(object sender, GridViewRowEventArgs e) {
  if (e.Row.RowType == DataControlRowType.DataRow) {
    /*      
            	gvXMLBind.DataKeys[e.Row.RowIndex][0]
              gvXMLBind.DataKeys[e.Row.RowIndex][1],   
              gvXMLBind.DataKeys[e.Row.RowIndex][2] 
              and so on for multiple values
         */
  }
}

Conclusion

Usage of DataKeyNames attribute is a less error prone way to access the primary key columns of gridview.

Posted By -	Karan Gupta

Posted On -	Friday, January 6, 2012

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