execution of AfterInsert caused by: System.FinalException: Record is read-only: (CMRules)

Question

Hoping someone can help me fix this. I understand that this error is because I'm trying to access a record that kicked off the trigger. I'm just not sure how to resolve it. Any help would be appreciated.

trigger EmailSummaryCreate on wbsendit__Campaign_Activity__c (after insert, after update) {

//List of summary records that needs to be created 
List<CMRules__Email_Tracking_Summary__c> SummaryToInsert = new 
List<CMRules__Email_Tracking_Summary__c>();

//    set for only the campaign names in the current context
set<string> uKeyHistory = new set<string>();
for(wbsendit__Campaign_Activity__c hKey : trigger.new){
   if(hKey.CMRules__Unique_Key__c != null){
       uKeyHistory.add(hKey.CMRules__Unique_Key__c);
   }
 }

 Map<String,CMRules__Email_Tracking_Summary__c> matchingHistMap = new 
 Map<String,CMRules__Email_Tracking_Summary__c>();
 for(CMRules__Email_Tracking_Summary__c sum : [SELECT Id, 
 CMRules__Unique_Key__c 
 FROM CMRules__Email_Tracking_Summary__c 
 where CMRules__Unique_Key__c IN :uKeyHistory]){
   matchingHistMap.put(sum.CMRules__Unique_Key__c, sum);
}  

List<wbsendit__Campaign_Activity__c> historyFieldtoUpdate = new List<wbsendit__Campaign_Activity__c>();

// map of existing summaries records
 Map<string, Id> uKey = new Map<string, Id>();
 for(CMRules__Email_Tracking_Summary__c u : [SELECT Id, 
 CMRules__Unique_Key__c 
 FROM CMRules__Email_Tracking_Summary__c 
 where CMRules__Unique_Key__c IN :uKeyHistory]){
   uKey.put(u.CMRules__Unique_Key__c, u.Id); 
} 

 for(wbsendit__Campaign_Activity__c h : trigger.new){

   boolean      key1 = uKey.containsKey(h.CMRules__Unique_Key__c);
   list<string> key2 = uKey.values();
   //list<string> key4 = matchingHistMap.values();
   list<string> key3 = h.CMRules__Unique_Key__c.split(':', 0);

   if(uKey.containsKey(h.CMRules__Unique_Key__c)){   

 h.CMRules__Email_Tracking_Summary__c = matchingHistMap.get(h.CMRules__Unique_Key__c).Id;

                historyFieldtoUpdate.add(h);              

       }else {             
           //create new summary record
           CMRules__Email_Tracking_Summary__c s = new CMRules__Email_Tracking_Summary__c();              
           s.CMRules__Campaign_Name__c = h.name;
           s.CMRules__Contact__c = h.wbsendit__Contact__c;

          SummaryToInsert.add(s);                        
       }
    }
   insert SummaryToInsert;
   update historyFieldtoUpdate;
 }

Answer 1

I was able to resolve this error by changing it to a before insert/update trigger, and removing the update DML since the before trigger.new takes care of the dml.