I have an inventory table.  It is the items of inventory only.  There is no transactions of inventory bought (in) or use (out).  As inventory prices change on purchase invoices the information is manually updated.  I have decided I would like to track the history of prices.  I have a child-table to hold the price and the invoice date.  I need to populate the original purchase price field with the most recent entry in the portal. 

 

Other fields on the layout reference the purchase price field.  I have related the parent-table to the child-table by a serial number on the parent-table.  How do I populate the inventory record from entry on the portal? 

Sort the relationship descending by date; then the first record via that relationship is the most recent one, and you can use mySortedChildTable::price as an auto-enter option.