Hi Varaprasad,

Thank you for your reply!

I'm still getting the error below when I try to update the other opportunity recordtypes. The trigger works great for the recordtype 'Conference' but it gives an error for the other recordtypes. I want the trigger to work for the opportunity recordtype 'Conference' ONLY. The trigger shouldn't fire for any other recordtype.

Error:Apex trigger AttendeesHandling caused an unexpected exception, contact your administrator: AttendeesHandling: execution of AfterUpdate caused by: System.QueryException: List has no rows for assignment to SObject: ()
 

trigger AttendeesHandling on Opportunity (after insert,after delete,after update) {

list<Id> rlist1=new list<Id> ();
        list<Product2 > rlsit=new list<Product2>();
 Id oppRecordTypeId = Schema.SObjectType.Opportunity.getRecordTypeInfosByName().get('Conference').getRecordTypeId();
//////////// insert and update operation
        
 if(trigger.isinsert || trigger.isupdate){
    for(Opportunity o : trigger.new)
   
    {
        if(o.recordtypeid == oppRecordTypeId){
            rlist1.add(o.Discount_code_LU__c);  
        }
    }
 
  Product2 p2=[select id,Attendees__c from Product2 WHERE id in:rlist1];
    
  
  for(Opportunity opp:trigger.new){
   if(opp.recordtypeid == oppRecordTypeId){
   p2.Attendees__c=opp.Attendee_Name__c ;
  

   rlsit.add(p2);
   }
    } update rlsit; 
    
  }
   
 /////////////// Delete operation start   
 
    if(trigger.isdelete){
    for(Opportunity o : trigger.old)
    if(o.recordtypeid == oppRecordTypeId){
        
    {
        
        rlist1.add(o.Discount_code_LU__c );     
    }
    }
  Product2 p2=[select id,Attendees__c from Product2 WHERE id in:rlist1 LIMIT 1];
    
  
  for(Opportunity opp:trigger.old){
   
   p2.Attendees__c=opp.Attendee_Name__c ;
 
   rlsit.add(p2);
    } update rlsit; 
    
    }
}