Product Rule to check existing value in EFF attribute. Duplicate check rule.

Summary:

We have created an EFF on item for capturing UPC code. We want to make sure each item has unique UPC code.

Content (please ensure you mask any confidential information):

Hi All,

We have created an EFF on item for capturing UPC code. We want to make sure each item has unique UPC code.

During item creation if user enters the an UPC code, which already exists in the system, then the product rule should fire and inform user of existing UPC code. also same should work while updating UPC.

How can we achieve this ? also we have already used matching option in item class configuration for another combination.