Trigger to Pull related contact's details on Task page when new task creates

Question

I have a requirement. Contact related to Task, I need to pull his functional role (custom field) on Task page layout. So whenever I create or edit a Task and relate with any contact so his/her functional role (Custom field) Value should populate automatic on Task Page field(Functional role).

Please help! How can I achieve it? I tried formula field but unable to get. I tried through trigger but it is not working. Please check my code and let me know what I am doing wrong.

Please find below code:

// This trigger fires on newly inserted or reparented Tasks associated with conortunities,
// and stores the conty's current functional role value in the contact   functional role field
trigger updatefunctionalrole1 on Task(before insert, before update) {
    // Create a map between the contact ID and its functional role value
    Map < ID, String > confunrole1 = new Map < ID, String > ();
    List < Task > conTasks = new List < Task > ();
    // Loop through the triggered Tasks and add all of the contact IDs (for those associated with conortunities)
    for (Task t: trigger.new) {
        // Only Tasks associated with conortunities
        if (t.whoID != null && (String.valueOf(t.whoID)).startsWith('003')) {
            // And only newly inserted Tasks or those being reparented to an contact
            if (trigger.isInsert || (trigger.isUpdate && t.WhoID != trigger.oldMap.get(t.id).WhoID)) {
                confunrole1.put(t.whoID, '');
                conTasks.add(t);
            }
        }
    }
    // Query the conortunities and add their functional role to the map
    for (contact con: [SELECT Functional_Role__c FROM contact WHERE ID IN: confunrole1.keySet()]) {
        confunrole1.put(con.id, con.Functional_Role__c);
    }
    // Update the contact functional role field on the Task with the relevant value
    for (Task t: trigger.new) {
        t.functional_role__c = confunrole1.get(t.whoID);
    }
}

Kindly suggest what to do?

Answer 1

If you have any WFR or processes that update the record after insert due to this:

for (Task t: trigger.new) {
        t.functional_role__c = confunrole1.get(t.whoID);
    }

the field will be nulled as the value does not exist in the map due to this

if (t.whoID != null && (String.valueOf(t.whoID)).startsWith('003')) {
            // And only newly inserted Tasks or those being reparented to an contact
            if (trigger.isInsert || (trigger.isUpdate && t.WhoID != trigger.oldMap.get(t.id).WhoID)) {
                confunrole1.put(t.whoID, '');
                conTasks.add(t);
            }
        }

as the WHOID did not change and thus the map will not contain the whoID

You will have to rethink your trigger to not run on update in the same context where an insert occurred so that the resultant update does not null the field. Or at a minimum check the map for the key being present