Hello,

I currently have a trigger to count the number of tasks related to an Account. The trigger works for the most part, it does not work when an Account is merged with another Account. Can someone assist in helping me find why the code is not recounting the activity upon the change of the What.ID on the task?

Below is the code.


trigger SumTasksTrigger on Task (after insert, after update, after delete) {

    set<Id> set_id = new set<Id>();
    
    List<Account> acc_list = new List<Account>();
    
    if(Trigger.isInsert || Trigger.isUpdate){
        for(Task T: Trigger.new){
            set_id.add(T.WhatId);
            
        }
        
    }
    
    else if(Trigger.isDelete){
        for(Task T: Trigger.old){
            set_id.add(T.WhatId);
            
        }
        
    }
    
    if(Trigger.isAfter &&(Trigger.isInsert || trigger.isUpdate ||  Trigger.isDelete)){
        acc_list = [SELECT Id, Number_of_Tasks__c,(SELECT Id FROM Tasks WHERE Status = 'Completed' AND (CS_Activity__c = FALSE)) FROM Account WHERE Id IN: set_id];
        
        for(Account acc: acc_list){
            if(acc_list.size()>0)
                acc.Number_of_Tasks__c = acc.Tasks.size();
            else
                acc.Number_of_Tasks__c = 0;
        
    }
    
    if(!acc_list.isEmpty())
        update acc_list;

}

}