How to update EmailMessage(activity history) associated with a lead

Question

In continuation with this question:

Background: I send a SingleApexMessage from apex code and want to associate it with a Lead so that a record of Activity History is created when this email is sent. For this, I am doing a setTargetObjectId with Lead Id on this email before sending it. This creates an activity history on Lead.

Requirement: 2 custom fields on this activity history should be populated as well.

Here is what I tried:

Approach 1: Query for EmailMessage and update it. Problem here is how to fetch EmailMessage related to Lead, which field identifies this?

Approach 2: Do not do a setTargetObjectId, instead create a new EmailMessage and populate it with all custom and standard fields. Problem here is how to relate this with Lead?

Answer 1

If we assume that the activity created by your code will be the most recently created activity on that Lead, you can do a SOQL query for

SELECT Id FROM Task WHERE Type = 'Email' AND WhoId = :myLead.Id ORDER BY CreatedDate DESC LIMIT 1

(obviously, filter as much as you can to avoid any possible errors) and that should give you the most recently created activity for that Lead.

I don't know if activities are created synchronously or asynchronously, so you'll need to test this out. But that would be the first way I'd try it.