trigger opportunityProduct on OpportunityLineItem (after insert) {
   
   
   Set<Id> oppId = new Set<Id>();
   
   for(OpportunityLineItem opp : Trigger.new)
   {
       oppId.add(opp.OpportunityId);
       
   }
   
   List<Opportunity> oppList = new List<Opportunity>();
   List<String> products = new List<String>();
   
   
   for(Opportunity opp : [Select Name,(Select Name,product2Id,product2.Name_Details__c from OpportunityLineItems) from Opportunity where Id in:oppId ])
   {
       for(OpportunityLineItem oppLine : opp.OpportunityLineItems)
       {
           if(OpportunityLineItem.Name != null)
           {
               products.add(oppLine.product2.Name_Details__c);
               
           }
       }
       opp.Product_Details__c = String.join(products,', ');
       oppList.add(opp);
       
   }
      update oppList;
}




batchclass i have written


global class productNameOnOpportunity implements Database.Batchable<sObject>{
   global Database.QueryLocator start(Database.BatchableContext BC){
       String query = 'Select Name,Product_Details__c (Select Name,product2Id,product2.Name_Details__c from OpportunityLineItems) from Opportunity';
       return Database.getQueryLocator(query);
   }
   
   global void execute(Database.BatchableContext info, List<Opportunity> Opp)
   {
       List<String> names = new List<String>();
       List<Opportunity> oppList = new List<Opportunity>();
       for(OpportunityLineItem oppLine : Opp)
       {
           if(OpportunityLineItem.Name != null)
           {          
               names.add(OpportunityLineItem.product2.Name_Details__c);
               Opp.Product_Details__c = String.join(names,',');
               oppList.add(Opp);
           }
       }
       if(oppList.size()>0)
       {
           update oppList;
       }  
   }    
   global void finish(Database.BatchableContext info){
       
   }
}