Formula field doesn't retain old values in the trigger

Question

I have scenario 1 - A formula field on Account (custom_type__c) which references the Contact's email as - Primary_Contact__r.Email Whenever Primary Contact's email id is changed , Custom Type is updated on Account, which fires account trigger. However, Trigger.Old doesn't retain the old values. Example- If Primary Contact's email id is [email protected] , Custom Type on [email protected]. Now, email id of Primary Contact's is updated to [email protected] , so Custom Type on Account0 [email protected] , which fires account trigger. When I print below-

System.debug('In After Update NEW ' + a.custom_type__c); System.debug('In After Update Old ' + Trigger.OldMap.get(a.Id).custom_type__c)

Both the above statements [email protected] . 1)Why Trigger.OldMap() doesn't retain the old values?

I have scenario 2- I have changed the reference of the same formula field(custom_type__c) to the account name.Now Custom_Type__c = Name (Refers name of the account), in this case Trigger.OldMap retains the old values of the name.Why does it retain in scenario 2 but not in scenario 1?

Answer 1

This is the expected behavior. In Account trigger only changes to Account trigger Context records can be checked.

Therefore, if you want to handle changes for Primary_Contact fields, please consider writing code in Contact trigger (presumably Primary_Contact__c is a lookup to Contact).

Explanation:

Scenario 1:

1. Contact Record is updated.
2. Contact triggers are run.
3. Contact record changes are committed.
4. Account trigger is triggered. Here old values for the Contact are not present.

Scenario 2:

1. Account record is updated.
2. Account trigger is run. Old values for the formula are present because it references Account fields.
3. Account record changes are committed