Ensure DFF value for sequential number is unique

Summary:

Content (required):

We have created a DFF on the expense report header for a sequential number for the report. There is one DFF that uses SQLto select the next number available and another DFF that utilizes that number to concatenate a prefix. So the report header displays the DFF as ex. XYZ9000001, XYZ9000002, etc. We've discovered that when multiple users create expense reports at the same time, the number can be duplicated. Assuming this is due to the report not being saved so the value is not commited to the database. Is there a way to ensure the DFF for