Help me to retreive Account data in trigger

Question

I am creating a service record when opportunity is closed won and product code in opportunity line item is null. I am filling the new service record with the values from opportunity line item and opportunity, now they want data from account object, please help me to figure out this When i uncomment the Account Acc....i get invalid foreign key relationship:opportunitylineitem.op

for (OpportunityLineItem oli:[SELECT OpportunityId,Product2.name
                              FROM OpportunityLineItem 
                              where ProductCode = null 
                              AND Opportunityid IN :opps]){
             Opportunity op = Trigger.newMap.get(oli.OpportunityId);
             // Account Acc = Trigger.newMap.get(oli.op.AccountId);
             lServ.add(new Services__c(
                     Account__c = op.accountid, 
                     Policy_Number__c=op.Policy_Number__c,
                     Opportunity__c=oli.OpportunityId,
                     Vendor__c =op.Issuing_Carrier__c,
                  // Source__c=Acc.Source__c,
                     Start_Date__c=op.Effective_Date__c, 
                     End_Date__c= op.Expiration_Date__c,
                     Product_Name__c=oli.Product2.name));                                                     
    }
    if (lServ.size() > 0){
        insert lServ;
    }

Answer 1

Trigger.newMap will return a Map of triggered object with the new changes. So if you are writing the trigger on Opportunity, it will return a map of IDs to the new versions of the Opportunity records.
So after getting the Opportunity object from the Map, you are capable of retrieving it's parent with the existing relationships like below.

Account acc = op.Account;

Have a look at Trigger Context variables and note that,

this map is only available in before update, after insert, and after update triggers.

NOTE: Even though this is not directly relate to the question follow the best practices specially when writing triggers so that your trigger support bulk records and not hitting governor limits.