Hi guys, 
please take a look.
I have two objects expenditures and purchase orders(PO). They both have lookup relationship between them. And whenever a PO status is completed, it can't be edited. So whenever we want to edit the existing PO- we need to create another po with in the original po. So the newely created po has POCN__c=1 and original po has POCN__C = 0. Every po has its own expenditure list. Now, I need to display the list of expenditures of POCN__C= 0 on POCN__C = 1. I wrote the following code. I'm not that good at coding. i got the output but whenever i tried to click on the link it says URL no longer exists,,
Apex - 
public class ListOfExpenditures
{
public string  previousExp{get;set;}
public string  currentExp{get;set;}
public List<string> listOfStringName{get;set;}


public ListOfExpenditures(ApexPages.StandardController controller) 
{ 
Id prId = null;
        
//prId = ApexPages.CurrentPage().getparameters().get('id');
//Purchase_Order__c  po=[select Original_Purchase_Order__c from Purchase_Order__c where id='a4R7A000000S7E4'];

Purchase_Order__c  po=[select Original_Purchase_Order__c from Purchase_Order__c where id= :ApexPages.currentPage().getParameters().get('id')];


id myid=po.Original_Purchase_Order__c;
purchase_order__c po1=[select name,(select id,Name from Expenditures__r) from Purchase_Order__c  where id=:myid];

//System.debug(po1.name);
Id expId = null;
List<id> listOfIds;
listOfIds = new List<Id>();
for(Expenditures__c e:po1.Expenditures__r)
{
//System.debug(e.id);
expId = e.id;
listOfIds.add(expId);
}
listOfStringName = new List<string>();
List<Expenditures__c> exp = [select id,Name,Amount__c from Expenditures__c where id in :listOfIds];
for (Expenditures__c el : exp)
{
previousExp = string.valueOf(el.name);
listOfStringName.add(previousExp);
}
}
}
vf - 
<apex:page standardcontroller="Purchase_Order__c" extensions="ListOfExpenditures" >
    <apex:pageBlock title="List"  >    
        <apex:form >
       
        
                       
                           <apex:outputLink > {!listOfStringName}</apex:outputLink>
                      
                        
        </apex:form>
    </apex:pageBlock>
</apex:page>