I have a user lookup field on the Account that I want to control ownership for all the Account's Contacts. So for example, if the Account is owned by User1, and my user lookup field says User2, all the Contacts should also be owned by User2. If that lookup field is changed to User3, all Contacts should be reassigned to User3.
I tried to build a workflow rule for this, but it doesn't look like you can change the owner dynamically -- I can trigger the update, but I can't specify the field update to change it to match the lookup field (have to specify one user to change to).
Is this only possible via a trigger?