Create map of User and corresponding List of Accounts

Question

I have an object where exist an Account and user lookup fields. Now records of the object will have always user and Account combination as unique. It means U1 -A1 combination can not exist in multiple records of the object. I have to create a map of User Id and List of it's corresponding Account Ids. I tried below but it somehow not even prints in debug log. So I am unable to understand where is my mistake. Can someone please help here?

Apex Code

Map<Id,Set<Id>> MapOfTierObj = new Map<Id,Set<Id>>();
// Change in map assign 
for(Tier_abv__c Tr: scope)
{
   if(!MapOfTierObj.containsKey(Tr.Core_Panel_User_abv__c))
   {
       MapOfTierObj.put(Tr.Core_Panel_User_abv__c, new Set<ID>{Tr.Account_abv__c});
   }else{
         MapOfTierObj.get(Tr.Core_Panel_User_abv__c).add(Tr.Account_abv__c);
          system.debug('Add Accounts to existing@'+MapOfTierObj.get(Tr.Core_Panel_User_abv__c)); }    
   }

    system.debug('MapOfTierObj@'+MapOfTierObj);
    // Change in Map assign : Completed

Here the scope comes from here:

global Database.QueryLocator start(Database.BatchableContext BC) {
        Query =  'SELECT id,Account_abv__c,Account_abv__r.Commercial_Core_Panel_Target_abv__c,Core_Panel_User_abv__c '+
            'from Tier_abv__c Where Core_Panel_User_abv__c != NULL AND Account_abv__r.Commercial_Core_Panel_Target_abv__c = True '+
             'order by Core_Panel_User_abv__c asc';

          Abbvie_Custom_Settings__c AbvSetngs = Abbvie_Custom_Settings__c.getInstance('Main');
                  if(AbvSetngs !=null)
                  {
                   ListName = AbvSetngs.Commercial_Core_Panel_Target_List_Name__c;   
                  }
                  else 
                  {
                      ListName = 'My Core Panel with Recent Comm Visit';
                  }

        return Database.getQueryLocator(query);
    }

Answer 1

You are missing putting set value to map. I will recommend writing it in below form:

for(Tier_abv__c Tr: scope)
{
   Set<Id> idSet=new Set<Id> ();
   if(MapOfTierObj.containsKey(Tr.Core_Panel_User_abv__c))
      idSet=MapOfTierObj.get(Tr.Core_Panel_User_abv__c);
   idSet.add(Tr.Account_abv__c)
   MapOfTierObj.put(Tr.Core_Panel_User_abv__c,idSet);

}

Here is adiitional information to explain what was wrong with your code:

else{
         MapOfTierObj.get(Tr.Core_Panel_User_abv__c).add(Tr.Account_abv__c);
          system.debug('Add Accounts to existing@'+MapOfTierObj.get(Tr.Core_Panel_User_abv__c)); }    
   }

Above code snippet will definitely add a value to set but will not update your map with revised set. So you could have written this as:

MapOfTierObj.put(Tr.Core_Panel_User_abv__c,MapOfTierObj.get(Tr.Core_Panel_User_abv__c).add(Tr.Account_abv__c));