Hi SK_Singh,

A DML Statement on Page display is frowned apon by Salesforce.com and it is disallowed in the controller (Page Display) method in your Customer Controller Class however it's still technically possible via the VF page action.

As you have given us no actual sample use case, I will make one up for you.

USE CASE

I have an email that will be emailed to a customer with 2 links. Issue Solved and Issue Not Solved. I require this to update the field Status__c of a single record in my custom object Customer_Issue__c.

1) Create an email template on the Customer_Issue__c and merge the Id of the record into 2 links below.

• http://mydomain.force.com/MyCustomVFPage?ObjectId=a1cN0000000Vr6R&ResponseCode=Solved
• http://mydomain.force.com/MyCustomVFPage?ObjectId=a1cN0000000Vr6R&ResponseCode=NotSolved

2) Create a Visualforce Page named MyCustomVFPage and show this on your default website (Setup | Develop | Sites | Default website | Site Visualforce Pages )

VF Page

<apex:page id="Page" showHeader="false" controller="MyCustomVFPage_CTR" action="{!InitPage}" cache="false">
	<apex:form>
		Thank you for your custom.
	</apex:form>
</apex:page>

Apex Class

public class MyCustomVFPage_CTR {
	public String ObjectId {get;set;}
	public String ResponseCode {get;set;}
	public MyCustomVFPage_CTR () {
		ObjectId = ApexPages.currentPage().getParameters().get('ObjectId');
		ResponseCode = ApexPages.currentPage().getParameters().get('ResponseCode');
	}
	public PageReference InitPage() {
		List<Customer_Issue__c> CustomerIssues = [SELECT Id, Status__c FROM Customer_Issue__c WHERE Id=:ObjectId LIMIT 1];
		if(!CustomerIssues.IsEmpty()){
			CustomerIssues[0].Status__c = ResponseCode;
			UPDATE CustomerIssues;
		}
	}
}