Trigger : How to track once an event moves from "Open Activities" to "Activity History"?

Question

I have an event record E on my Opportunity O.

E starts at 07/03/2018 11:00 AM and ends at 07/03/2018 11:30 AM.

Before the event E appears in "Open Activities" and once the event start time is past it appears in "Activity History".

Is there any way to track the transition ?.

I need to perform few operations once an event moves from "Open Activities" to "Activity History" but since the transition is not DML based (i could be wrong) I am not sure how I can write a trigger for it.

Answer 1

See also: What fields determine what is displayed in Open Activities vs. Activity History

For Task records, you can write a trigger that compares the old and new value of IsClosed.

trigger Task on Task (before update)
{
    // handler, service, etc omitted for brevity
    for (Task record : trigger.new)
    {
        Task oldRecord = trigger.oldMap.get(record.Id);
        if (record.IsClosed && !oldRecord.IsClosed)
        {
            // do stuff
        }
    }
}

For Event records, you will need a scheduled job in which you look for records whose StartDateTime is less than Datetime.now(), but also greater than the last time the job was run. There are a variety of ways to do that. The simplest may be to run the job daily and look for records which started yesterday, but you could also use a Hierarchy Custom Setting or query for the last time the job was run. I'm sure there are other approaches which would work as well. If you run it daily, that would look something like:

public class MyEventJob implements Scheduleable
{
    public void execute(ScheduleableContext context)
    {
        for (Event record : [
            SELECT Id FROM Event
            WHERE StartDateTime = YESTERDAY
        ]){
            // do stuff
        }
    }
}