Hi,

As I am able to update on single records but not working when its on bulk.

here is my code///
public class UpdateActivityHistoryCallCount {
    
    
    //To update the Count of Activity History in Lead object
    
    public static void countActivityHistoryOnLead(list<Task> newTaskList,list<Task> oldTaskList){
        set<Id> LeadIds=new set<Id>();
        list<Lead> leadList=new list<Lead>();
        Map<Id, String> error = new Map<Id, String>();
        
        if(trigger.isInsert || trigger.isUnDelete || trigger.isUpdate){
            for(Task tsk:newTaskList){
                if(string.valueOf(tsk.WhoId).startsWith('00Q'))
                    LeadIds.add(tsk.WhoId);
                
            }
        }
        if(trigger.isDelete || trigger.isUpdate){
            for(Task tk:oldTaskList){
                if(string.valueOf(tk.WhoId).startsWith('00Q'))
                    LeadIds.add(tk.whoId);
                
            }
        }
        if(LeadIds.size()>0){
            for(Lead l:[select id,(select id,subject,Due_Date__c,CreatedDate
                                   from tasks where (subject='Call' and status='Completed'
                                                     and  Due_Date__c < Today) or (subject='Call' and status='Completed' and Due_Date__c =  null)  ) 
                        from lead where id in :LeadIds limit 50000])
                leadList.add(new lead(id=l.Id,Call_count__c=l.tasks.size()));
            
            
        }
        Database.SaveResult[] results= database.update (leadList,false);
        system.debug('@@@@' +results);
        
    }
    
}

Thanks