Validate by Calculation II: Records in Portal must be unique
FileMaker Pro v11: I am using a portal (Item List) to record line items related to a parent table (Work Order). The match field is Work Order, this is a many-to-many relationship. I need to validate that only unique Serial Numbers (a field in Item List table) are entered in any one Work Order. I can't simply require the Serial Number field to be unique, because any Serial Number could potentially appear in more than one Work Order. How can I verify (with an alert) that while in a single Work Order record, all Serial Numbers remain unique? If more detail is needed to answer, I'll be happy to elaborate. Thanks in advance!