DFF validation code

Hi SMEs

I have a sceanrio and help me to build code in DFF attribute.

License plate DFF enabled with one DFF attribute1

in mobile LPN update page, we are invoking this DFF. We scan the LPN in LPN field and then we scan the attribute1 field(another LPN number)

we want to validate after update button pressed in mobile page.

Data come to base table..right?

At that time, the attribute1 data should be valaidated against LPN field of the same table. If LPN and Attribute1 are equal, then the data should be updated in attribute1. if not then it shoud not update, give error message to mobile page(if possible).