How to populate a field on Contact from Related Task

Question

I have a field on Task Test_Time__c (Date/Time). How can I fetch this field and populate on Last_Login_Time__c on Related Contact record?

Below is task on Contact

Below is the related Contact

Tried to add this trigger on Task

trigger lastLogin on Task (after insert, after update, before insert, before update) { 

Map<Id, List<Task>> taskWhatIds = new Map<Id, List<Task>>{};

    for (Task t : trigger.new) {
        if (t.WhatId != null) {
        List<Task> tasks = taskWhatIds.get(t.WhatId);
        if (tasks == null) {
            tasks = new List<Task>();
            taskWhatIds.put(t.WhatId, tasks);
        }
        tasks.add(t); 
    }
}

for (Contact c: [Select Id, Last_login_time__c FROM Contact WHERE Id IN :taskWhatIds.keySet()]){
    for (task t : taskWhatIds.get(c.id)){
        t.test_time__c = c.last_login_time__c;
    }
}
}

Answer 1

Your trigger doesn't do anything to the Contact at all.

for (Contact c: [Select Id, Last_login_time__c FROM Contact WHERE Id IN :taskWhatIds.keySet()]){
    for (task t : taskWhatIds.get(c.id)){
        t.test_time__c = c.last_login_time__c;
    }
}

You need to make two specific changes here:

1. You're assigning to a field on t, the Task, rather than c, the Contact. You need to fix this by modifying the Contact.
2. You also do not perform DML. From a Task trigger, you must fire an update DML to persist your changes to a Contact. You need to build a List of contacts to update and do update contactList at the end of your trigger.

I'm pretty sure you don't need this running after insert, after update, before insert, before update. after insert should be enough.