Adding Product via VF and getting Pricebookid from Opportunity

Question

In my viualforce page I am adding products - I don't want to hardcode the references to the products, I want the button to pull the proper product per Opportunity. Why does my line not work to find the proper pricebook entry? The method:

public PageReference AddJuiceProduct (){

       Opportunity TheOpp = (Opportunity)sc.GetRecord();
       NewLineItem.OpportunityId=TheOpp.id;
       NewLineItem.PricebookEntryId=[select id from PricebookEntry where name =: 'Juice' and Pricebook2id=:op.Pricebook2Id].id;
        NewLineItem.Quantity=1;
       ETC code...
       insert NewLineItem;

If I hardcode the reference to the product the insert works. Example:

NewLineItem.PricebookEntryId='123456798798794654';

Why doesn't this query work? thanks!

    NewLineItem.PricebookEntryId=[select id from PricebookEntry 
                                 where name =: 'Juice' 
                                 and Pricebook2id=:op.Pricebook2Id].id;

Answer 1

I had two errors in this: First, I declared the Opportunity variable TheOpp

 Opportunity TheOpp = (Opportunity)sc.GetRecord();

but then in my query used op.pricebook2id - this compiled b/c OP was declared as a variable elsewhere.

Next, I needed to add the fields to the controller and in the GetRecord:

Controller.addFields(new List<String>{'Name', 'PriceBook2Id'});