Access the values from Trigger.oldMap

Question

I'm setting up an Apex trigger and want to access the description values of the old records before a merge. Once I have the 3 description values, I want to combine all the descriptions together during the merge instead of keeping one.

This is what I have so far. Code after each // is sudo code. Am I close?

 trigger MergeLeadDescriptions on Lead (before delete, after delete) {
  if (Trigger.isBefore) {
     Trigger.oldMap.keySet()
     // String a = oldMap.id1.Description
     // String b = oldMap.id2.Description
     // String c = oldMap.id3.Description
  } 
  // MasterRecordId.Description = a + " " + b + " " + c
 }

Here are docs on the process of triggers and merging.

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_triggers_merge_statements.htm

I'm having a hard time understanding them..

Thanks!

Update:

This code seems to be working except for the very end...

 trigger MergeLeadDescriptions on Lead (before delete, after delete) {

 String a, b, c;

 if (Trigger.isBefore) {

   a = Trigger.Old[0].Description;
   b = Trigger.Old[1].Description;
   c = Trigger.Old[2].Description;

 } 
 else {

 Trigger.old.MasterRecordId.Description = a + ' ' + b + ' ' + c;

 }

}

I'm getting an error "Initial term of field expression must be a concrete SObject: List"

Answer 1

I don't think this can be accomplished in a trigger. I'm fairly certain that you'll need to delegate the logic to a class so that you can make use of static variables to hold the information across the different trigger contexts. When merging records, before delete triggers fire, followed by after delete and finally an update is fired on the master record. I also believe the MasterRecordId is only available in the after delete context.

I haven't tested this, and it's almost certainly not the most efficient pattern, but something like this should get you what you need.

Trigger:

trigger MergeLeadDescriptions on Lead (before update, before delete, after delete){

    if(Trigger.isUpdate && Trigger.isBefore){
        TriggerHandler.beforeUpdate(Trigger.new);
    }
    else if(Trigger.isDelete && Trigger.isBefore){
        TriggerHandler.beforeDelete(Trigger.old);
    }
    else if(Trigger.isDelete && Trigger.isAfter){
        TriggerHandler.afterDelete(Trigger.old);
    }

}

Class:

public class TriggerHandler {

    //Static variables
    public static String deletedDescriptions;
    public static Set<Id> masterRecordIds = new Set<Id>();

    public static void beforeUpdate (List<Lead> updatedLeads){
        for(Lead l : newLeads){
            if(masterRecordIds.contains(l.Id)){
                //Append deleted descriptions to Master description.
                l.Description += deletedDescriptions;
            }
        }
    }

    public static void beforeDelete(List<Lead> deletedLeads){
        //Append Description to static variable deletedDescriptions
        for(Lead l : deletedLeads){
            deletedDescriptions += ' ';
            deletedDescriptions += l.Description;
        }
    }

    public static void afterDelete(List<Lead> deletedLeads){
        //Gather the MasterRecordId
        for(Lead l : deletedLeads){
            if(l.MasterRecordId != null){
                masterRecordIds.add(l.MasterRecordId);
            }           
        }
    }

}

Answer 2

Trigger.OldMap is a a map of IDs to the old versions of the sObject records while Trigger.Old Returns a list of the old versions of the sObject records So if you want to access value you can do that in following way

trigger MergeLeadDescriptions on Lead (before delete, after delete) {
  if (Trigger.isBefore) {
     //Trigger.oldMap.keySet()
      String a = Trigger.Old[0].Field1__c
      String b = Trigger.Old[0].Field2__c
      String c = Trigger.Old[0].Field3__c
  } 
  // MasterRecordId.Description = a + " " + b + " " + c
 }