invoice.ex

# Is this preferable...

defmodule Invoice do
  ...
  
  def execute(%Invoice{id: invoice_id} = invoice, %AddLineItem{} = add) do
    # Generate %LineItemAdded and %InvoiceTotalUpdated using Commanded.Aggregate.Multi
    # The %InvoiceTotalUpdated event would have the new total on it, calculated based on the
    # existing invoice total + the new line item's total
  end
  
  def apply(%Invoice{} = invoice, %LineItemAdded{} = added) do
    # Add line item to the Invoice aggregate's line_items list
  end
  
  def apply(%Invoice{} = invoice, %InvoiceTotalUpdated = updated) do
    # Update the total for the Invoice aggregate
  end
end

# or is this...

defmodule Invoice do
  ...
  
  def execute(%Invoice{id: invoice_id} = invoice, %AddLineItem{} = add) do
    # Generate %LineItemAdded, which has the new line item's data in addition
    # to a invoice_total, calculated based on the existing invoice total + the new line item's total
  end
  
  def apply(%Invoice{} = invoice, %LineItemAdded{} = added) do
    # Add line item to the Invoice aggregate's line_items list, AND update the total
  end
end