Getting revised map <id, string> data back into original list under same id

Question

I seem to be having difficulty getting data from a map back into a list so that it corresponds to the correct Id and field it was originally associated with after it's been modified in a trigger. For some reason, its just not coming to me how to do this efficiently.

This is part of a trigger that creates an event from an opportunity. After inserting the list of new events, here's what I'm trying to do:

   // Iterate through the Save Results
   for(Integer i=0; i<InsertResults.size(); i++){
     If (!InsertResults[i].isSuccess()) oppIdToErrMssg.put( InsertResults[i].Id , 'Error reported was: ' + InsertResults[i].getErrors()[0].getMessage() + '/n' + IdtoEvntNotes.get(InsertResults[i].Id)); 
   }  

   // The above code works. 
   // It appends any save results error messages to the Event_Notes__c field

   // add system debug results to IdtoEvntNotes
   // the loop below, inserts the results from above to an existing map
   // Yes, the two steps could have been combined (something for later)  

  Integer idErrSz = OppIdErrSet.size();

  If (idErrSz != 0) {
     for (Id idz : oppIdToErrMssg.keySet()) {
        IdtoEvntNotes.put(idz, oppIdToErrMssg.get(idz));    
     }

     // here's where I'm having the problem!!!
     // retrieve EvntNotes entries to insert into the original opp list for updating    

     Integer ENts = OppEvntNtsErr.size();
     list<opportunity> EvntNtsErrs = new list<opportunity>();

     // ***** the code below is not correct *****
     // but illustrates what I want to accomplish!
     for ( Integer i=0; i< ENts; i++){
        EvntNtsErrs[i].Id = IdtoEvntNotes.get(IdtoEvntNotes.key[i]);
        EvntNtsErrs[i].Event_Notes__c = IdtoEvntNotes.get(IdtoEvntNotes.key[i]);
     }

     try{
     update OppEvntNtsErr;
        } catch(DmlException e) {
        // Add any exception handling code;
        }

  }

With a keyset(), can one pull out "key[i]"?? or do you have to do an implicit loop that would look something like:

for (Id theKey:theMap.keySet() )
{
   do something with theKey; \\ ex: listname.Id = theKey ??
   do something with theMap.get(theKey); \\ ex: listname.fieldname = theMap.get(theKey) ??
}

It seems as though this should be trivial, but my brain is just mush today. When searching around, I couldn't seem to find anything that provided a solution or example that seemed to be what I needed.

Thanks!

Answer 1

The order of insertion is not preserved in a Map, so you wouldn't be able to access it using a numerical index iterator.

Iterate over a list and pull out the corresponding key from the Map KeySet eg

List<Opportunity> oppList = ....

Map<Id, Opportunity> oppMap = ...

for(Opportunity opp : oppList)
System.debug(opp.Id + ' = ' + oppMap.get(opp.Id)); //pull out corresponding element from keyset