I'm working on a validation rule for field service and I'm wondering if this is possible.
We have the Product Request parent object, and the Product Request Line Item child object. There is a field called "Part Number" on the PRLI - only one part number exists on a PRLI, so a new PRLI needs to be created for each part number. Due to interface concerns, we want to prevent a PR from being saved if there are more than one PRLI with the same value in the Part Number field (because the tech should be adjusting the quantity on the PRLI, not creating multiple PRLIs for the same part number). Is it possible to write a validation rule on the parent object that checks a field on the child for duplicates?