Get old and new Opportunity owner name from opportunity trigger

Question

I am using :

trigger.oldMap.get(op.ID).Owner.Name;

and it is returning me null. Is there a way I can get both old and new opportunity owner name. Using query I am able to get only the new owner name.

Map<ID,Opportunity> allOpp1 = new Map<ID,Opportunity>([Select ID, Account.ID, Opportunity.Owner.Name, Opportunity.Owner.Email, Opportunity.Owner.FIrstName, Owner.ID from Opportunity]);    
for(Opportunity op : trigger.new){

        String body = 'Dear '+allOpp1.get(op.Id).Owner.FirstName+'\n Opportunity: '+op.Name+' has be moved to the new Owner '+trigger.oldMap.get(op.ID).Owner.Name;               
}        

Thanks in advance.

Answer 1

You cannot get the parent or child information from trigger.new or trigger.old.

The trigger.new(Map)/trigger.old(Map) variable only has access to the fields in current object and no access to child object or lookup fields.

You will have to create a formula field (Lets say OwnerName__c) on the object (I guess your trigger is on opportunity so you'll have to create a formula field on opportunity) which gets the owner name from opportunity.

Then you can perform comparison

if(trigger.oldMap.get(op.ID).OwnerName__c != op.OwnerName__c ){
    //Perform something
}

Note this won't work for a before insert trigger.

I prefer a formula because it will take into account older opportunities also.