Hi,

You have to use inner SOQL query for your requirement to fulfill.

Try to use below updated batch class code.

Batch class:

global class RollUpSummaryMaps implements Database.Batchable<sObject>{    
    list<OpportunityLineItem> opporto =new List<OpportunityLineItem>();
    list<Opportunity> optylist =new List<Opportunity>();
    Opportunity optyupdate= new Opportunity();
    public Double curecy=0;    
    global Database.QueryLocator start(Database.BatchableContext BC){
        // Access initialState here
        String lineitem='SELECT id,ListPrice, OpportunityId, PricebookEntryId FROM OpportunityLineItem';        
        // Database.ge
        System.debug('The Query@@@@@@@@'+lineitem);
        return Database.getQueryLocator(lineitem);
    }
    
    global void execute(Database.BatchableContext BC,List<Sobject> batch){    
        Map<ID, Opportunity> iMap = new Map<ID, Opportunity>([select Id,testvantage__Updatevalue__c,(select id,UnitPrice from opportunityLineitems) From Opportunity ]);
        //Map<ID, OpportunityLineItem> mapOppty = new Map<ID, OpportunityLineItem>([SELECT Id,UnitPrice, OpportunityId, PricebookEntryId FROM OpportunityLineItem where OpportunityId IN :iMap.keySet()]);
        Integer optylinesize=iMap.size();
        System.debug('NEWDEBUGOptyLineItem @@@@@@@@@@@@@@############'+optylinesize);
        Integer optysize=mapOppty.size();
        System.debug('NEWDEBUGOptyList @@@@@@@@@@@@@@############'+optysize);
        try{
            if(iMap != null && iMap.size()>0){
                for(Opportunity opp: iMap.values){
                    for(OpportunityLineItem lineitem:opp.opportunityLineitems){
                        if(lineitem.UnitPrice != null){
                            opp.testvantage__Updatevalue__c += lineitem.UnitPrice;
                        }
                    }
                    OptyList.add(opp);
                }
                if(OptyList.size()>0){
                    update OptyList;
                }
            }
        }catch(DMLException e){
            system.debug('The batch jobs were not added to the queue successfully: '+e);
        }    
    }    
    global void finish(Database.BatchableContext BC){
    
    }
}

Important :
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Thank You,
Hitesh Patel
SFDC Certified Developer & Administrator & Advanced Administrator & Sales cloud consultant
My Blog:- http://mrjavascript.blogspot.in/