What is the "Ash way" to auto update related resources ?
Let's say that I have an invoice (postgres) resource and that it has_many lines. Let's say that I want the total_amount field of my invoice resource to be updated with the sum(amount) of all lines every time that a line is created, updated or deleted. What would be the idiomatic way to do that ? I understand that I should probably use aggregates and changes with an after_action, but I have a bit of a hard time to see exactly how to articulates all the pieces together.
