Trigger is not updating the first task record on Contact

Question

I have this trigger on Task which should take the first record of tasks and update on their contact id. But, when I tried updating the big file through data loader, It doesn't take the first record. How do I make sure that when I bulk upload, every contact id gets updated with their first record of the task? Thank you in advance!

trigger contactActivityTrigger on Task (after insert, after update) {
if (Trigger.isafter && Trigger.isInsert){
              contactActivityHandler.insertContact(Trigger.New);

     } 
     if(Trigger.isafter && Trigger.isUpdate){
         contactActivityHandler.updateOldContact(Trigger.New ,Trigger.Old);

     }
}


public class contactActivityHandler {

public static void insertContact(List<Task> tks){ // Trigger.New comes as List here
    Set <Id> ContactIds = new Set<Id>();
    List <Contact> ContactList = new List<Contact>();

    for(Task t :tks) 
    {
        if(t.whoId!=null)
        {
            Schema.SObjectType tType= t.whoId.getSObjectType();
            if(tType == Contact.Schema.SObjectType)
            {
                ContactIds.add(t.WhoId);
            }
        }
    }
    //Querying the related Contacts based on whoId on Task
    Map<Id,Contact> ContactMap =  new Map<Id,Contact>([select id, Last_Contact_Date__c,Name,
                                                       Last_Activity_TypeOfInteraction__c, 
                                                       LastActivityDate, Last_Activity_Subject__c,
                                                       Last_Activity_Date__c, Last_Activity_Name__c 
                                                       from Contact where id in:ContactIds]);
    for(Task t :tks)
    {

            for(Contact l : ContactMap.Values())
            {  
              If(t.ActivityDate >=l.Last_Contact_Date__c)
                {
                l.Last_Activity_Subject__c = t.subject;
                l.Last_Activity_Date__c = t.ActivityDate;
                l.Last_Activity_Name__c = l.Name;
                l.Last_Activity_TypeOfInteraction__c = t.Type_of_Interaction__c;
                l.Last_Activity_Assigned_to__c = t.Owner.Name;
                ContactList.add(l);
                     System.debug('Printining that INSERTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT ran');  
                }
             } 

    }  

    map<id,Contact> conMap = new map<id,Contact>();
    conMap.putAll(ContactList);

    // updating the Lead

    if(conMap.size()>0)
    {


        update conMap.Values();
    }
}//End of insert Contact



public static void updateOldContact(List<Task> tks, List<Task>tksOld){ // Trigger.New comes as List here

    Set<Id> ContactIds = new Set<Id>();
    Set<Id> OldContactIds = new Set<Id>(); //to get old contact ids
    List<Contact> ContactList = new List<Contact>();
    List<Contact> OldContactList = new List<Contact>();
    List<Contact> AllUpdateContactList = new List<Contact>();

    for(Task ot :tks)
    {
        if(ot.whoId!=null)
        {
            Schema.SObjectType otType= ot.whoId.getSObjectType();
            if(otType == Contact.Schema.SObjectType)
            {       
                ContactIds.add(ot.WhoId); //Get new contact Id
            }
        }
    }//End of Second loop         

            List<Contact> relatedContacts = [select id,Last_Contact_Date__c,
                                                                  Name, Last_Activity_TypeOfInteraction__c, 
                                                                  LastActivityDate, Last_Activity_Subject__c,
                                                                  Last_Activity_Date__c, Last_Activity_Name__c,
                                             (select id,Subject,ActivityDate,Owner.Name, Type_of_Interaction__c  from Tasks Order By ActivityDate DESC LIMIT 1)
                                                                  from Contact where id in:ContactIds];


            for (Contact relatedContact : relatedContacts)
                {
                    relatedContact.Last_Activity_Subject__c = relatedContact.Tasks[0].Subject;
                    relatedContact.Last_Activity_Assigned_to__c=relatedContact.Tasks[0].Owner.Name;
                    relatedContact.Last_Activity_Date__c = relatedContact.Tasks[0].ActivityDate;
                    relatedContact.Last_Activity_Name__c =  relatedContact.Name;
                    relatedContact.Last_Activity_TypeOfInteraction__c = relatedContact.Tasks[0].Type_of_Interaction__c;

                     System.debug('Printining that UPDATEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE ran'); 


                    // etc.
                }
                update relatedContacts;


}//End of Update Old Contact

}//End of Class

Answer 1

Use a subquery to get the related Task records. Right now you are only pulling one Task, no matter how many Contact records are passed through. You want one per.

[
    SELECT ...
        (SELECT ... FROM Tasks ORDER BY ActivityDate DESC LIMIT 1)
    FROM Contact WHERE ...
]

Please note you will not even need a Map anywhere here, and there is no benefit to checking for empty collections before DML. So you can roughly simplify to the following:

Set<Id> contactIds = new Set<Id>();
// populate the same

List<Contact> relatedContacts = [/*same query as I mention above*/];
for (Contact relatedContact : relatedContacts)
{
    relatedContact.Last_Activity_Subject__c = relatedContact.Tasks[0].Subject;
    // etc.
}
update relatedContacts;

Answer 2

I'm not sure if this is the only problem, but you are trying to use = instead of IN:

task where WhoId =: ContactIds

->

task where WhoId IN: ContactIds

NOTE: Not an error but you already have the Contacts in a map. Use that instead of having a loop within a loop.

Answer 3

From what I can tell you want to identify when the contact on a task changes. When this happens, you want to update the new contact with the most recent task's information?

I would do it in the contact trigger.

public class contactService {
    // Should be in before update trigger
    // a contact cannot have tasks on insert
    public static void getRecentTaskInformation(List<Contact> contacts) {
        List<Contact> contactsWithLastTasks = [
            SELECT Id, Last_Activity_Subject__c, Last_Activity_Date__c,
                Last_Activity_Name__c , Last_Activity_Assigned_to__c ,
                Last_Activity_TypeOfInteraction__c , Name, (
                    SELECT Subject, ActivityDate, Owner.Name, 
                        Type_of_Interaction__c
                    FROM Tasks
                    ORDER BY ActivityDate DESC 
                    LIMIT 1
                )
            FROM Contact WHERE Id IN :contacts
        ];

        for (Contact c : contactsWithLastTasks) {
            if (!c.tasks.isEmpty()) {
                Task lastTask = c.tasks[0];

                c.Last_Activity_Subject__c = lastTask.subject;
                c.Last_Activity_Date__c = lastTask.activityDate;
                c.Last_Activity_Assigned_to__c = lastTask.Owner.Name;
                c.Last_Activity_Name__c  = c.Name;
                c.Last_Activity_TypeOfInteraction__c  = lastTask.Type_of_Interaction__c;
            }
        }
    }
}

Then in your task trigger you just need to update the contacts that you want to re-calculate:

trigger TaskTrigger on Task (after insert, after update) {
    List<Contact> contactsToRecalc = new List<Contact>();

    for (Task t : Trigger.New) {
        if (trigger.oldMap == null || t.WhoId != trigger.oldMap.get(t.Id).whoId) {
            contactsToRecalc.add(new Contact(Id=t.whoId));
            contactsToRecalc.add(new Contact(Id=trigger.oldMap.get(t.Id).Id));
        }
    }

    update contactsToRecalc;
}