Merge operation: how to detect merge in BEFORE_DELETE trigger?

Question

Is there any way to detect that a BEFORE_DELETE trigger was caused by a merge operation? I need to manually reparent/fix/delete some related child records before they are reparented automatically by the merge operation. But since MasterRecordId is only filled in in the AFTER_DELETE trigger, when all related records are already reparented, there is no way to know if the related record belonged to the winning or losing record.

Answer 1

The solution is a split trigger. This needs a static variable for you to store the data in.

trigger handleMerge on X (before delete, after delete) {
  if(Trigger.isBefore) {
    TriggerHandlerForX.storeChildData(Trigger.old);
  } else {
    TriggerHandlerForX.processMerges(Trigger.old);
  }
}

public class TriggerHandlerForX {
  static sObject[] children;
  public static void storeChildData(X[] parents) {
    children = [select ... from children where parent in :parents];
  }
  public static void processMerges(X[] parents) {
    for(X parent: parents) {
      if(hasMasterId(parent)) {
        handleOtherChanges(children);
      }
    }
  }
}

This is obviously pseudo-code, but hopefully it demonstrates how to handle this. Let the automatic updates take care of themselves, but you can process the children in any special manner you need. Be aware that they'll still have the "old" Id values, even though they may have the new values in the database. We made the copy of the records before the database change happened.

Answer 2

I think that perhaps you can accomplish this by using a Boolean on the records that are possible to merge which I believe are: Lead, Contact, Account, Person Account.

Add a custom field, check box, to those objects.

Named: Merged?

When merging records you can tick that custom field. This way to can flag records that were merged. On triggers you need to look at the value of the custom field to execute further logics around these records.